pp_hot.c

/*    pp_hot.c
 *
 *    Copyright (C) 1991, 1992, 1993, 1994, 1995, 1996, 1997, 1998, 1999, 2000,
 *    2001, 2002, 2003, 2004, 2005, 2006, 2007, 2008 by Larry Wall and others
 *
 *    You may distribute under the terms of either the GNU General Public
 *    License or the Artistic License, as specified in the README file.
 *
 */

/*
 * Then he heard Merry change the note, and up went the Horn-cry of Buckland,
 * shaking the air.
 *
 *                  Awake!  Awake!  Fear, Fire, Foes!  Awake!
 *                               Fire, Foes!  Awake!
 *
 *     [p.1007 of _The Lord of the Rings_, VI/viii: "The Scouring of the Shire"]
 */

/* This file contains 'hot' pp ("push/pop") functions that
 * execute the opcodes that make up a perl program. A typical pp function
 * expects to find its arguments on the stack, and usually pushes its
 * results onto the stack, hence the 'pp' terminology. Each OP structure
 * contains a pointer to the relevant pp_foo() function.
 *
 * By 'hot', we mean common ops whose execution speed is critical.
 * By gathering them together into a single file, we encourage
 * CPU cache hits on hot code. Also it could be taken as a warning not to
 * change any code in this file unless you're sure it won't affect
 * performance.
 */

#include "EXTERN.h"
#define PERL_IN_PP_HOT_C
#include "perl.h"
#include "regcomp.h"
#include "feature.h"

/* Hot code. */


#ifdef PERL_RC_STACK

/* common code for pp_wrap() and xs_wrap():
 * free any original arguments, and bump and shift down any return
 * args
 */

STATIC void
S_pp_xs_wrap_return(pTHX_ I32 nargs, I32 old_sp)
{
    I32 nret = (I32)(PL_stack_sp - PL_stack_base) - old_sp;
    assert(nret >= 0);

    /* bump any returned values */
    if (nret) {
        SV **svp = PL_stack_sp - nret + 1;
        while (svp <= PL_stack_sp) {
            SvREFCNT_inc(*svp);
            svp++;
        }
    }

    PL_curstackinfo->si_stack_nonrc_base = 0;

    /* free the original args and shift the returned valued down */
    if (nargs) {
        SV **svp = PL_stack_sp - nret;
        I32 i = nargs;
        while (i--) {
            SvREFCNT_dec(*svp);
            *svp = NULL;
            svp--;
        }

        if (nret) {
            Move(PL_stack_sp - nret + 1,
                 PL_stack_sp - nret - nargs + 1,
                 nret, SV*);
        }
        PL_stack_sp -= nargs;
    }
}

/* pp_wrap():
 * wrapper function for pp() functions to turn them into functions
 * that can operate on a reference-counted stack, by taking a non-
 * reference-counted copy of the current stack frame, calling the real
 * pp() function, then incrementing the reference count of any returned
 * args.
 *
 * nargs or nlists indicate the number of stack arguments or the
 * number of stack lists (delimited by MARKs) which the function expects.
 */
OP*
Perl_pp_wrap(pTHX_ Perl_ppaddr_t real_pp_fn, I32 nargs, int nlists)
{
    PERL_ARGS_ASSERT_PP_WRAP;

    if (!rpp_stack_is_rc())
        /* stack-already non-RC; nothing needing wrapping */
        return real_pp_fn(aTHX);

    OP *next_op;
    I32 old_sp = (I32)(PL_stack_sp - PL_stack_base);

    assert(nargs  >= 0);
    assert(nlists >= 0);
    assert(AvREAL(PL_curstack));

    PL_curstackinfo->si_stack_nonrc_base = PL_stack_sp - PL_stack_base + 1;

    if (nlists) {
        assert(nargs == 0);
        I32 mark  = PL_markstack_ptr[-nlists+1];
        nargs = (PL_stack_sp - PL_stack_base) - mark;
        assert(nlists <= 2); /* if ever more, make below a loop */
        PL_markstack_ptr[0]  += nargs;
        if (nlists == 2)
            PL_markstack_ptr[-1] += nargs;
    }

    if (nargs) {
        /* duplicate all the arg pointers further up the stack */
        rpp_extend(nargs);
        Copy(PL_stack_sp - nargs + 1, PL_stack_sp + 1, nargs, SV*);
        PL_stack_sp += nargs;
    }

    next_op = real_pp_fn(aTHX);

    /* we should still be a split stack */
    assert(AvREAL(PL_curstack));
    assert(PL_curstackinfo->si_stack_nonrc_base);

    S_pp_xs_wrap_return(aTHX_ nargs, old_sp);

    return next_op;
}


/* xs_wrap():
 * similar in concept to pp_wrap: make a non-referenced-counted copy of
 * a (not refcount aware) XS sub's args, call the XS subs, then bump any
 * return values and free the original args */

void
Perl_xs_wrap(pTHX_ XSUBADDR_t xsub, CV *cv)
{
    PERL_ARGS_ASSERT_XS_WRAP;

    I32 old_sp = (I32)(PL_stack_sp - PL_stack_base);
    I32 mark  = PL_markstack_ptr[0];
    I32 nargs = (PL_stack_sp - PL_stack_base) - mark;

    /* we should be a fully refcounted stack */
    assert(AvREAL(PL_curstack));
    assert(!PL_curstackinfo->si_stack_nonrc_base);

    PL_curstackinfo->si_stack_nonrc_base = PL_stack_sp - PL_stack_base + 1;


    if (nargs) {
        /* duplicate all the arg pointers further up the stack */
        rpp_extend(nargs);
        Copy(PL_stack_sp - nargs + 1, PL_stack_sp + 1, nargs, SV*);
        PL_stack_sp += nargs;
        PL_markstack_ptr[0]  += nargs;
    }

    xsub(aTHX_ cv);

    S_pp_xs_wrap_return(aTHX_ nargs, old_sp);
}

#endif



/* Private helper function for Perl_rpp_replace_2_1_COMMON()
 * and rpp_popfree_2_NN().
 * Free the two passed SVs, whose original ref counts are rc1 and rc2.
 * Assumes the stack initially looked like
 *    .... sv1 sv2
 * and is now:
 *    .... X
 * but where sv2 is still on the slot above the current PL_stack_sp.
 */

void
Perl_rpp_free_2_(pTHX_ SV *const sv1,  SV *const sv2,
                       const U32 rc1,  const U32 rc2)
{

    PERL_ARGS_ASSERT_RPP_FREE_2_;

#ifdef PERL_RC_STACK
    if (rc1 > 1)
        SvREFCNT(sv1) = rc1 - 1;
    else {
        /* temporarily reclaim sv2 on stack in case we die while freeing sv1 */
        assert(PL_stack_sp[1] == sv2);
        PL_stack_sp++;
        Perl_sv_free2(aTHX_ sv1, rc1);
        PL_stack_sp--;
    }
    if (rc2 > 1)
        SvREFCNT(sv2) = rc2 - 1;
    else
        Perl_sv_free2(aTHX_ sv2, rc2);
#else
    PERL_UNUSED_VAR(sv1);
    PERL_UNUSED_VAR(sv2);
    PERL_UNUSED_VAR(rc1);
    PERL_UNUSED_VAR(rc2);
#endif
}



/* ----------------------------------------------------------- */


PP(pp_const)
{
    rpp_xpush_1(cSVOP_sv);
    return NORMAL;
}

PP(pp_nextstate)
{
    PL_curcop = (COP*)PL_op;
    TAINT_NOT;		/* Each statement is presumed innocent */
    rpp_popfree_to_NN(PL_stack_base + CX_CUR()->blk_oldsp);
    FREETMPS;
    PERL_ASYNC_CHECK();
    return NORMAL;
}

PP(pp_gvsv)
{
    assert(SvTYPE(cGVOP_gv) == SVt_PVGV);
    rpp_xpush_1(
            UNLIKELY(PL_op->op_private & OPpLVAL_INTRO)
                ? save_scalar(cGVOP_gv)
                : GvSVn(cGVOP_gv));
    return NORMAL;
}


/* also used for: pp_lineseq() pp_regcmaybe() pp_scalar() pp_scope() */

PP(pp_null)
{
    return NORMAL;
}

PP(pp_pushmark)
{
    PUSHMARK(PL_stack_sp);
    return NORMAL;
}

PP(pp_stringify)
{
    dTARGET;
    sv_copypv(TARG, *PL_stack_sp);
    SvSETMAGIC(TARG);
    rpp_replace_1_1_NN(TARG);
    return NORMAL;
}

PP(pp_gv)
{
    /* cGVOP_gv might be a real GV or might be an RV to a CV */
    assert(SvTYPE(cGVOP_gv) == SVt_PVGV ||
           (SvTYPE(cGVOP_gv) <= SVt_PVMG && SvROK(cGVOP_gv) && SvTYPE(SvRV(cGVOP_gv)) == SVt_PVCV));
    rpp_xpush_1(MUTABLE_SV(cGVOP_gv));
    return NORMAL;
}


/* also used for: pp_andassign() */

PP(pp_and)
{
    PERL_ASYNC_CHECK();
    {
        SV * const sv = *PL_stack_sp;
        if (!SvTRUE_NN(sv))
            return NORMAL;
        else {
            if (PL_op->op_type == OP_AND)
                rpp_popfree_1_NN();
            return cLOGOP->op_other;
        }
    }
}

/*
 * Mashup of simple padsv + sassign OPs
 * Doesn't support the following lengthy and unlikely sassign case:
 *    (UNLIKELY(PL_op->op_private & OPpASSIGN_CV_TO_GV))
 *  These cases have a separate optimization, so are not handled here:
 *    (PL_op->op_private & OPpASSIGN_BACKWARDS) {or,and,dor}assign
*/

PP(pp_padsv_store)
{
    OP * const op = PL_op;
    SV** const padentry = &PAD_SVl(op->op_targ);
    SV* targ = *padentry; /* lvalue to assign into */
    SV* const val = *PL_stack_sp; /* RHS value to assign */

    /* !OPf_STACKED is not handled by this OP */
    assert(op->op_flags & OPf_STACKED);

    /* Inlined, simplified pp_padsv here */
    if ((op->op_private & (OPpLVAL_INTRO|OPpPAD_STATE)) == OPpLVAL_INTRO) {
        save_clearsv(padentry);
    }

    /* Inlined, simplified pp_sassign from here */
    assert(TAINTING_get || !TAINT_get);
    if (UNLIKELY(TAINT_get) && !SvTAINTED(val))
        TAINT_NOT;

    if (
      UNLIKELY(SvTEMP(targ)) && !SvSMAGICAL(targ) && SvREFCNT(targ) == 1 &&
      (!isGV_with_GP(targ) || SvFAKE(targ)) && ckWARN(WARN_MISC)
    )
        warner(packWARN(WARN_MISC), "Useless assignment to a temporary");
    SvSetMagicSV(targ, val);

    assert(GIMME_V == G_VOID);
    rpp_popfree_1_NN();
    return NORMAL;
}


/* A mashup of simplified AELEMFAST_LEX + SASSIGN OPs */

PP(pp_aelemfastlex_store)
{
    OP * const op = PL_op;
    SV* const val = *PL_stack_sp; /* RHS value to assign */
    AV * const av = MUTABLE_AV(PAD_SV(op->op_targ));
    const I8 key   = (I8)PL_op->op_private;
    SV * targ = NULL;

    /* !OPf_STACKED is not handled by this OP */
    assert(op->op_flags & OPf_STACKED);

    /* Inlined, simplified pp_aelemfast here */
    assert(SvTYPE(av) == SVt_PVAV);

    /* inlined av_fetch() for simple cases ... */
    if (!SvRMAGICAL(av) && key >=0 && key <= AvFILLp(av)) {
        targ = AvARRAY(av)[key];
    }
    /* ... else do it the hard way */
    if (!targ) {
        SV **svp = av_fetch(av, key, 1);

        if (svp)
            targ = *svp;
        else
            DIE(aTHX_ PL_no_aelem, (int)key);
    }

    /* Inlined, simplified pp_sassign from here */
    assert(TAINTING_get || !TAINT_get);
    if (UNLIKELY(TAINT_get) && !SvTAINTED(val))
        TAINT_NOT;

    /* This assertion is a deviation from pp_sassign, which uses an if()
     * condition to check for "Useless assignment to a temporary" and
     * warns if the condition is true. Here, the condition should NEVER
     * be true when the LHS is the result of an array fetch. The
     * assertion is here as a final check that this remains the case.
     */
    assert(!(SvTEMP(targ) && SvREFCNT(targ) == 1 && !SvSMAGICAL(targ)));

    SvSetMagicSV(targ, val);

    assert(GIMME_V == G_VOID);
    rpp_popfree_1_NN();
    return NORMAL;
}

PP(pp_sassign)
{
    /* sassign keeps its args in the optree traditionally backwards.
       So we pop them differently.
    */
    SV *left  = PL_stack_sp[0];
    SV *right = PL_stack_sp[-1];

    if (PL_op->op_private & OPpASSIGN_BACKWARDS) { /* {or,and,dor}assign */
        SV * const temp = left;
        left = right; right = temp;
        PL_stack_sp[0]  = left;
        PL_stack_sp[-1] = right;
    }
    assert(TAINTING_get || !TAINT_get);
    if (UNLIKELY(TAINT_get) && !SvTAINTED(right))
        TAINT_NOT;

    if (UNLIKELY(PL_op->op_private & OPpASSIGN_CV_TO_GV)) {
        /* *foo =\&bar */
        SV * const cv = SvRV(right);
        const U32 cv_type = SvTYPE(cv);
        const bool is_gv = isGV_with_GP(left);
        const bool got_coderef = cv_type == SVt_PVCV || cv_type == SVt_PVFM;

        if (!got_coderef) {
            assert(SvROK(cv));
        }

        /* Can do the optimisation if left (LVALUE) is not a typeglob,
           right (RVALUE) is a reference to something, and we're in void
           context. */
        if (!got_coderef && !is_gv && GIMME_V == G_VOID) {
            /* Is the target symbol table currently empty?  */
            GV * const gv = gv_fetchsv_nomg(left, GV_NOINIT, SVt_PVGV);
            if (SvTYPE(gv) != SVt_PVGV && !SvOK(gv)) {
                /* Good. Create a new proxy constant subroutine in the target.
                   The gv becomes a(nother) reference to the constant.  */
                SV *const value = SvRV(cv);

                SvUPGRADE(MUTABLE_SV(gv), SVt_IV);
                SvPCS_IMPORTED_on(gv);
                SvRV_set(gv, value);
                SvREFCNT_inc_simple_void(value);
                rpp_replace_2_1_NN(left);
                return NORMAL;
            }
        }

        /* Need to fix things up.  */
        if (!is_gv) {
            /* Need to fix GV.  */
            SV *sv = MUTABLE_SV(gv_fetchsv_nomg(left,GV_ADD, SVt_PVGV));
            rpp_replace_1_1_NN(sv);
            left = sv;
        }

        if (!got_coderef) {
            /* We've been returned a constant rather than a full subroutine,
               but they expect a subroutine reference to apply.  */
            if (SvROK(cv)) {
                ENTER_with_name("sassign_coderef");
                SvREFCNT_inc_void(SvRV(cv));
                /* newCONSTSUB takes a reference count on the passed in SV
                   from us.  We set the name to NULL, otherwise we get into
                   all sorts of fun as the reference to our new sub is
                   donated to the GV that we're about to assign to.
                */
                SvRV_set(right, MUTABLE_SV(newCONSTSUB(GvSTASH(left), NULL,
                                                      SvRV(cv))));
                SvREFCNT_dec_NN(cv);
                LEAVE_with_name("sassign_coderef");
            } else {
                /* What can happen for the corner case *{"BONK"} = \&{"BONK"};
                   is that
                   First:   ops for \&{"BONK"}; return us the constant in the
                            symbol table
                   Second:  ops for *{"BONK"} cause that symbol table entry
                            (and our reference to it) to be upgraded from RV
                            to typeblob)
                   Thirdly: We get here. cv is actually PVGV now, and its
                            GvCV() is actually the subroutine we're looking for

                   So change the reference so that it points to the subroutine
                   of that typeglob, as that's what they were after all along.
                */
                GV *const upgraded = MUTABLE_GV(cv);
                CV *const source = GvCV(upgraded);

                assert(source);
                assert(CvFLAGS(source) & CVf_CONST);

                SvREFCNT_inc_simple_void_NN(source);
                SvREFCNT_dec_NN(upgraded);
                SvRV_set(right, MUTABLE_SV(source));
            }
        }

    }
    if (
      rpp_is_lone(left) && !SvSMAGICAL(left) &&
      (!isGV_with_GP(left) || SvFAKE(left)) && ckWARN(WARN_MISC)
    )
        warner(packWARN(WARN_MISC), "Useless assignment to a temporary");
    SvSetMagicSV(left, right);
    if (LIKELY(GIMME_V == G_VOID))
        rpp_popfree_2_NN(); /* pop left and right */
    else {
        /* pop right, leave left on the stack */
        assert(PL_stack_sp[-1] == right);
        assert(PL_stack_sp[0]  == left);
        *--PL_stack_sp = left;
#ifdef PERL_RC_STACK
        SvREFCNT_dec_NN(right);
#endif
    }

    return NORMAL;
}

PP(pp_cond_expr)
{
    PERL_ASYNC_CHECK();
    bool ok = SvTRUE_NN(*PL_stack_sp);
    rpp_popfree_1_NN();
    return (ok ? cLOGOP->op_other : cLOGOP->op_next);
}

PP(pp_unstack)
{
    PERL_CONTEXT *cx;
    PERL_ASYNC_CHECK();
    TAINT_NOT;		/* Each statement is presumed innocent */
    cx  = CX_CUR();
    rpp_popfree_to_NN(PL_stack_base + CX_CUR()->blk_oldsp);
    FREETMPS;
    if (!(PL_op->op_flags & OPf_SPECIAL)) {
        assert(CxTYPE(cx) == CXt_BLOCK || CxTYPE_is_LOOP(cx));
        CX_LEAVE_SCOPE(cx);
    }
    return NORMAL;
}


/* The main body of pp_concat, not including the magic/overload and
 * stack handling.
 * It does targ = left . right.
 * Moved into a separate function so that pp_multiconcat() can use it
 * too.
 */

PERL_STATIC_INLINE void
S_do_concat(pTHX_ SV *left, SV *right, SV *targ, U8 targmy)
{
    bool lbyte;
    STRLEN rlen;
    const char *rpv = NULL;
    bool rbyte = FALSE;
    bool rcopied = FALSE;

    if (TARG == right && right != left) { /* $r = $l.$r */
        rpv = SvPV_nomg_const(right, rlen);
        rbyte = !DO_UTF8(right);
        right = newSVpvn_flags(rpv, rlen, SVs_TEMP);
        rpv = SvPV_const(right, rlen);	/* no point setting UTF-8 here */
        rcopied = TRUE;
    }

    if (TARG != left) { /* not $l .= $r */
        STRLEN llen;
        const char* const lpv = SvPV_nomg_const(left, llen);
        lbyte = !DO_UTF8(left);
        sv_setpvn(TARG, lpv, llen);
        if (!lbyte)
            SvUTF8_on(TARG);
        else
            SvUTF8_off(TARG);
    }
    else { /* $l .= $r   and   left == TARG */
        if (!SvOK(left)) {
            if ((left == right                          /* $l .= $l */
                 || targmy)                             /* $l = $l . $r */
                && ckWARN(WARN_UNINITIALIZED)
                )
                report_uninit(left);
            SvPVCLEAR(left);
        }
        else {
            SvPV_force_nomg_nolen(left);
        }
        lbyte = !DO_UTF8(left);
        if (IN_BYTES)
            SvUTF8_off(left);
    }

    if (!rcopied) {
        rpv = SvPV_nomg_const(right, rlen);
        rbyte = !DO_UTF8(right);
    }
    if (lbyte != rbyte) {
        if (lbyte)
            sv_utf8_upgrade_nomg(TARG);
        else {
            if (!rcopied)
                right = newSVpvn_flags(rpv, rlen, SVs_TEMP);
            sv_utf8_upgrade_nomg(right);
            rpv = SvPV_nomg_const(right, rlen);
        }
    }
    sv_catpvn_nomg(TARG, rpv, rlen);
    SvSETMAGIC(TARG);
}


PP(pp_concat)
{
    SV *targ = (PL_op->op_flags & OPf_STACKED)
                    ? PL_stack_sp[-1]
                    : PAD_SV(PL_op->op_targ);

    if (rpp_try_AMAGIC_2(concat_amg, AMGf_assign))
       return NORMAL;

    SV *right = PL_stack_sp[0];
    SV *left  = PL_stack_sp[-1];
    S_do_concat(aTHX_ left, right, targ, PL_op->op_private & OPpTARGET_MY);
    rpp_replace_2_1_NN(targ);
    return NORMAL;
}


/* pp_multiconcat()

Concatenate one or more args, possibly interleaved with constant string
segments. The result may be assigned to, or appended to, a variable or
expression.

Several op_flags and/or op_private bits indicate what the target is, and
whether it's appended to. Valid permutations are:

    -                                  (PADTMP) = (A.B.C....)
    OPpTARGET_MY                       $lex     = (A.B.C....)
    OPpTARGET_MY,OPpLVAL_INTRO         my $lex  = (A.B.C....)
    OPpTARGET_MY,OPpMULTICONCAT_APPEND $lex    .= (A.B.C....)
    OPf_STACKED                        expr     = (A.B.C....)
    OPf_STACKED,OPpMULTICONCAT_APPEND  expr    .= (A.B.C....)

Other combinations like (A.B).(C.D) are not optimised into a multiconcat
op, as it's too hard to get the correct ordering of ties, overload etc.

In addition:

    OPpMULTICONCAT_FAKE:       not a real concat, instead an optimised
                               sprintf "...%s...". Don't call '.'
                               overloading: only use '""' overloading.

    OPpMULTICONCAT_STRINGIFY:  the RHS was of the form
                               "...$a...$b..." rather than
                               "..." . $a . "..." . $b . "..."

An OP_MULTICONCAT is of type UNOP_AUX. The fixed slots of the aux array are
defined with PERL_MULTICONCAT_IX_FOO constants, where:


    FOO       index description
    --------  ----- ----------------------------------
    NARGS     0     number of arguments
    PLAIN_PV  1     non-utf8 constant string
    PLAIN_LEN 2     non-utf8 constant string length
    UTF8_PV   3     utf8 constant string
    UTF8_LEN  4     utf8 constant string length
    LENGTHS   5     first of nargs+1 const segment lengths

The idea is that a general string concatenation will have a fixed (known
at compile time) number of variable args, interspersed with constant
strings, e.g. "a=$a b=$b\n"

All the constant string segments "a=", " b=" and "\n" are stored as a
single string "a= b=\n", pointed to from the PLAIN_PV/UTF8_PV slot, along
with a series of segment lengths: e.g. 2,3,1. In the case where the
constant string is plain but has a different utf8 representation, both
variants are stored, and two sets of (nargs+1) segments lengths are stored
in the slots beginning at PERL_MULTICONCAT_IX_LENGTHS.

A segment length of -1 indicates that there is no constant string at that
point; this distinguishes between e.g. ($a . $b) and ($a . "" . $b), which
have differing overloading behaviour.

*/

PP(pp_multiconcat)
{
    SV *targ;                /* The SV to be assigned or appended to */
    char *targ_pv;           /* where within SvPVX(targ) we're writing to */
    STRLEN targ_len;         /* SvCUR(targ) */
    SV **toparg;             /* the highest arg position on the stack */
    UNOP_AUX_item *aux;      /* PL_op->op_aux buffer */
    UNOP_AUX_item *const_lens; /* the segment length array part of aux */
    const char *const_pv;    /* the current segment of the const string buf */
    SSize_t nargs;           /* how many args were expected */
    SSize_t stack_adj;       /* how much to adjust PL_stack_sp on return */
    STRLEN grow;             /* final size of destination string (targ) */
    UV targ_count;           /* how many times targ has appeared on the RHS */
    bool is_append;          /* OPpMULTICONCAT_APPEND flag is set */
    bool slow_concat;        /* args too complex for quick concat */
    U32  dst_utf8;           /* the result will be utf8 (indicate this with
                                SVf_UTF8 in a U32, rather than using bool,
                                for ease of testing and setting) */
    /* for each arg, holds the result of an SvPV() call */
    struct multiconcat_svpv {
        const char   *pv;
        SSize_t       len;
    }
        *targ_chain,         /* chain of slots where targ has appeared on RHS */
        *svpv_p,             /* ptr for looping through svpv_buf */
        *svpv_base,          /* first slot (may be greater than svpv_buf), */
        *svpv_end,           /* and slot after highest result so far, of: */
        svpv_buf[PERL_MULTICONCAT_MAXARG]; /* buf for storing SvPV() results */

    aux   = cUNOP_AUXx(PL_op)->op_aux;
    stack_adj = nargs = aux[PERL_MULTICONCAT_IX_NARGS].ssize;
    is_append = cBOOL(PL_op->op_private & OPpMULTICONCAT_APPEND);

    /* get targ from the stack or pad */

    toparg = PL_stack_sp;
    if (PL_op->op_flags & OPf_STACKED) {
        stack_adj++;
        if (is_append) {
            /* for 'expr .= ...', expr is the bottom item on the stack */
            targ = PL_stack_sp[-nargs];
        }
        else {
            /* for 'expr = ...', expr is the top item on the stack */
            targ = *PL_stack_sp;
            toparg--;
        }
    }
    else {
        SV **svp = &(PAD_SVl(PL_op->op_targ));
        targ = *svp;
        if (PL_op->op_private & OPpLVAL_INTRO) {
            assert(PL_op->op_private & OPpTARGET_MY);
            save_clearsv(svp);
        }
        if (!nargs)
            /* $lex .= "const" doesn't cause anything to be pushed */
            rpp_extend(1);
    }

    grow          = 1;    /* allow for '\0' at minimum */
    targ_count    = 0;
    targ_chain    = NULL;
    targ_len      = 0;
    svpv_end      = svpv_buf;
                    /* only utf8 variants of the const strings? */
    dst_utf8      = aux[PERL_MULTICONCAT_IX_PLAIN_PV].pv ? 0 : SVf_UTF8;


    /* --------------------------------------------------------------
     * Phase 1:
     *
     * stringify (i.e. SvPV()) every arg and store the resultant pv/len/utf8
     * triplets in svpv_buf[]. Also increment 'grow' by the args' lengths.
     *
     * utf8 is indicated by storing a negative length.
     *
     * Where an arg is actually targ, the stringification is deferred:
     * the length is set to 0, and the slot is added to targ_chain.
     *
     * If a magic, overloaded, or otherwise weird arg is found, which
     * might have side effects when stringified, the loop is abandoned and
     * we goto a code block where a more basic 'emulate calling
     * pp_cpncat() on each arg in turn' is done.
     */

    for (SV **svp = toparg - (nargs - 1); svp <= toparg; svp++, svpv_end++) {
        U32 utf8;
        STRLEN len;
        SV *sv;

        assert(svpv_end - svpv_buf < PERL_MULTICONCAT_MAXARG);

        sv = *svp;

        /* this if/else chain is arranged so that common/simple cases
         * take few conditionals */

        if (LIKELY((SvFLAGS(sv) & (SVs_GMG|SVf_ROK|SVf_POK)) == SVf_POK)) {
            /* common case: sv is a simple non-magical PV */
            if (targ == sv) {
                /* targ appears on RHS.
                 * Delay storing PV pointer; instead, add slot to targ_chain
                 * so it can be populated later, after targ has been grown and
                 * we know its final SvPVX() address.
                 */
              targ_on_rhs:
                svpv_end->len = 0; /* zerojng here means we can skip
                                      updating later if targ_len == 0 */
                svpv_end->pv  = (char*)targ_chain;
                targ_chain    = svpv_end;
                targ_count++;
                continue;
            }

            len           = SvCUR(sv);
            svpv_end->pv  = SvPVX(sv);
        }
        else if (UNLIKELY(SvFLAGS(sv) & (SVs_GMG|SVf_ROK)))
            /* may have side effects: tie, overload etc.
             * Abandon 'stringify everything first' and handle
             * args in strict order. Note that already-stringified args
             * will be reprocessed, which is safe because the each first
             * stringification would have been idempotent.
             */
            goto do_magical;
        else if (SvNIOK(sv)) {
            if (targ == sv)
              goto targ_on_rhs;
            /* stringify general valid scalar */
            svpv_end->pv = sv_2pv_flags(sv, &len, 0);
        }
        else if (!SvOK(sv)) {
            if (ckWARN(WARN_UNINITIALIZED))
                /* an undef value in the presence of warnings may trigger
                 * side affects */
                goto do_magical;
            svpv_end->pv = "";
            len = 0;
        }
        else
            goto do_magical; /* something weird */

        utf8 = (SvFLAGS(sv) & SVf_UTF8);
        dst_utf8   |= utf8;
        ASSUME(len < SSize_t_MAX);
        svpv_end->len = utf8 ? -(SSize_t)len : (SSize_t)len;
        grow += len;
    }

    /* --------------------------------------------------------------
     * Phase 2:
     *
     * Stringify targ:
     *
     * if targ appears on the RHS or is appended to, force stringify it;
     * otherwise set it to "". Then set targ_len.
     */

    if (is_append) {
        /* abandon quick route if using targ might have side effects */
        if (UNLIKELY(SvFLAGS(targ) & (SVs_GMG|SVf_ROK)))
            goto do_magical;

        if (SvOK(targ)) {
            U32 targ_utf8;
          stringify_targ:
            SvPV_force_nomg_nolen(targ);
            targ_utf8 = SvFLAGS(targ) & SVf_UTF8;
            if (UNLIKELY(dst_utf8 & ~targ_utf8)) {
                 if (LIKELY(!IN_BYTES))
                    sv_utf8_upgrade_nomg(targ);
            }
            else
                dst_utf8 |= targ_utf8;

            targ_len = SvCUR(targ);
            grow += targ_len * (targ_count + is_append);
            goto phase3;
        }
        else if (ckWARN(WARN_UNINITIALIZED))
            /* warning might have side effects */
            goto do_magical;
        /* the undef targ will be silently SvPVCLEAR()ed below */
    }
    else if (UNLIKELY(SvTYPE(targ) >= SVt_REGEXP)) {
        /* Assigning to some weird LHS type. Don't force the LHS to be an
         * empty string; instead, do things 'long hand' by using the
         * overload code path, which concats to a TEMP sv and does
         * sv_catsv() calls rather than COPY()s. This ensures that even
         * bizarre code like this doesn't break or crash:
         *    *F = *F . *F.
         * (which makes the 'F' typeglob an alias to the
         * '*main::F*main::F' typeglob).
         */
        goto do_magical;
    }
    else if (targ_chain)
        /* targ was found on RHS.
         * Force stringify it, using the same code as the append branch
         * above, except that we don't need the magic/overload/undef
         * checks as these will already have been done in the phase 1
         * loop.
         */
        goto stringify_targ;

    /* unrolled SvPVCLEAR() - mostly: no need to grow or set SvCUR() to 0;
     * those will be done later. */
    SV_CHECK_THINKFIRST_COW_DROP(targ);
    SvUPGRADE(targ, SVt_PV);
    SvFLAGS(targ) &= ~(SVf_OK|SVf_IVisUV|SVf_UTF8);
    SvFLAGS(targ) |= (SVf_POK|SVp_POK|dst_utf8);

  phase3:

    /* --------------------------------------------------------------
     * Phase 3:
     *
     * UTF-8 tweaks and grow targ:
     *
     * Now that we know the length and utf8-ness of both the targ and
     * args, grow targ to the size needed to accumulate all the args, based
     * on whether targ appears on the RHS, whether we're appending, and
     * whether any non-utf8 args expand in size if converted to utf8.
     *
     * For the latter, if dst_utf8 we scan non-utf8 args looking for
     * variant chars, and adjust the svpv->len value of those args to the
     * utf8 size and negate it to flag them. At the same time we un-negate
     * the lens of any utf8 args since after this phase we no longer care
     * whether an arg is utf8 or not.
     *
     * Finally, initialise const_lens and const_pv based on utf8ness.
     * Note that there are 3 permutations:
     *
     * * If the constant string is invariant whether utf8 or not (e.g. "abc"),
     *   then aux[PERL_MULTICONCAT_IX_PLAIN_PV/LEN] are the same as
     *        aux[PERL_MULTICONCAT_IX_UTF8_PV/LEN] and there is one set of
     *   segment lengths.
     *
     * * If the string is fully utf8, e.g. "\x{100}", then
     *   aux[PERL_MULTICONCAT_IX_PLAIN_PV/LEN] == (NULL,0) and there is
     *   one set of segment lengths.
     *
     * * If the string has different plain and utf8 representations
     *   (e.g. "\x80"), then aux[PERL_MULTICONCAT_IX_PLAIN_PV/LEN]]
     *   holds the plain rep, while aux[PERL_MULTICONCAT_IX_UTF8_PV/LEN]
     *   holds the utf8 rep, and there are 2 sets of segment lengths,
     *   with the utf8 set following after the plain set.
     *
     * On entry to this section the (pv,len) pairs in svpv_buf have the
     * following meanings:
     *    (pv,  len) a plain string
     *    (pv, -len) a utf8 string
     *    (NULL,  0) left-most targ \ linked together R-to-L
     *    (next,  0) other targ     / in targ_chain
     */

    /* turn off utf8 handling if 'use bytes' is in scope */
    if (UNLIKELY(dst_utf8 && IN_BYTES)) {
        dst_utf8 = 0;
        SvUTF8_off(targ);
        /* undo all the negative lengths which flag utf8-ness */
        for (svpv_p = svpv_buf; svpv_p < svpv_end; svpv_p++) {
            SSize_t len = svpv_p->len;
            if (len < 0)
                svpv_p->len = -len;
        }
    }

    /* grow += total of lengths of constant string segments */
    {
        SSize_t len;
        len = aux[dst_utf8 ? PERL_MULTICONCAT_IX_UTF8_LEN
                           : PERL_MULTICONCAT_IX_PLAIN_LEN].ssize;
        slow_concat = cBOOL(len);
        grow += len;
    }

    const_lens = aux + PERL_MULTICONCAT_IX_LENGTHS;

    if (dst_utf8) {
        const_pv = aux[PERL_MULTICONCAT_IX_UTF8_PV].pv;
        if (   aux[PERL_MULTICONCAT_IX_PLAIN_PV].pv
            && const_pv != aux[PERL_MULTICONCAT_IX_PLAIN_PV].pv)
            /* separate sets of lengths for plain and utf8 */
            const_lens += nargs + 1;

        /* If the result is utf8 but some of the args aren't,
         * calculate how much extra growth is needed for all the chars
         * which will expand to two utf8 bytes.
         * Also, if the growth is non-zero, negate the length to indicate
         * that this is a variant string. Conversely, un-negate the
         * length on utf8 args (which was only needed to flag non-utf8
         * args in this loop */
        for (svpv_p = svpv_buf; svpv_p < svpv_end; svpv_p++) {
            SSize_t len, extra;

            len = svpv_p->len;
            if (len <= 0) {
                svpv_p->len = -len;
                continue;
            }

            extra = variant_under_utf8_count((U8 *) svpv_p->pv,
                                             (U8 *) svpv_p->pv + len);
            if (UNLIKELY(extra)) {
                grow       += extra;
                              /* -ve len indicates special handling */
                svpv_p->len = -(len + extra);
                slow_concat = TRUE;
            }
        }
    }
    else
        const_pv = aux[PERL_MULTICONCAT_IX_PLAIN_PV].pv;

    /* unrolled SvGROW(), except don't check for SVf_IsCOW, which should
     * already have been dropped */
    assert(!SvIsCOW(targ));
    targ_pv = (SvLEN(targ) < (grow) ? sv_grow(targ,grow) : SvPVX(targ));


    /* --------------------------------------------------------------
     * Phase 4:
     *
     * Now that targ has been grown, we know the final address of the targ
     * PVX, if needed. Preserve / move targ contents if appending or if
     * targ appears on RHS.
     *
     * Also update svpv_buf slots in targ_chain.
     *
     * Don't bother with any of this if the target length is zero:
     * targ_len is set to zero unless we're appending or targ appears on
     * RHS.  And even if it is, we can optimise by skipping this chunk of
     * code for zero targ_len. In the latter case, we don't need to update
     * the slots in targ_chain with the (zero length) target string, since
     * we set the len in such slots to 0 earlier, and since the Copy() is
     * skipped on zero length, it doesn't matter what svpv_p->pv contains.
     *
     * On entry to this section the (pv,len) pairs in svpv_buf have the
     * following meanings:
     *    (pv,  len)         a pure-plain or utf8 string
     *    (pv, -(len+extra)) a plain string which will expand by 'extra'
     *                         bytes when converted to utf8
     *    (NULL,  0)         left-most targ \ linked together R-to-L
     *    (next,  0)         other targ     / in targ_chain
     *
     * On exit, the targ contents will have been moved to the
     * earliest place they are needed (e.g. $x = "abc$x" will shift them
     * 3 bytes, while $x .= ... will leave them at the beginning);
     * and dst_pv will point to the location within SvPVX(targ) where the
     * next arg should be copied.
     */

    svpv_base = svpv_buf;

    if (targ_len) {
        struct multiconcat_svpv *tc_stop;
        char *targ_buf = targ_pv; /* ptr to original targ string */

        assert(is_append || targ_count);

        if (is_append) {
            targ_pv += targ_len;
            tc_stop = NULL;
        }
        else {
            /* The targ appears on RHS, e.g. '$t = $a . $t . $t'.
             * Move the current contents of targ to the first
             * position where it's needed, and use that as the src buffer
             * for any further uses (such as the second RHS $t above).
             * In calculating the first position, we need to sum the
             * lengths of all consts and args before that.
             */

            UNOP_AUX_item *lens = const_lens;
                                /* length of first const string segment */
            STRLEN offset       = lens->ssize > 0 ? lens->ssize : 0;

            assert(targ_chain);
            svpv_p = svpv_base;

            for (;;) {
                SSize_t len;
                if (!svpv_p->pv)
                    break; /* the first targ argument */
                /* add lengths of the next arg and const string segment */
                len = svpv_p->len;
                if (len < 0)  /* variant args have this */
                    len = -len;
                offset += (STRLEN)len;
                len = (++lens)->ssize;
                offset += (len >= 0) ? (STRLEN)len : 0;
                if (!offset) {
                    /* all args and consts so far are empty; update
                     * the start position for the concat later */
                    svpv_base++;
                    const_lens++;
                }
                svpv_p++;
                assert(svpv_p < svpv_end);
            }

            if (offset) {
                targ_buf += offset;
                Move(targ_pv, targ_buf, targ_len, char);
                /* a negative length implies don't Copy(), but do increment */
                svpv_p->len = -((SSize_t)targ_len);
                slow_concat = TRUE;
            }
            else {
                /* skip the first targ copy */
                svpv_base++;
                const_lens++;
                targ_pv += targ_len;
            }

            /* Don't populate the first targ slot in the loop below; it's
             * either not used because we advanced svpv_base beyond it, or
             * we already stored the special -targ_len value in it
             */
            tc_stop = svpv_p;
        }

        /* populate slots in svpv_buf representing targ on RHS */
        while (targ_chain != tc_stop) {
            struct multiconcat_svpv *p = targ_chain;
            targ_chain = (struct multiconcat_svpv *)(p->pv);
            p->pv  = targ_buf;
            p->len = (SSize_t)targ_len;
        }
    }


    /* --------------------------------------------------------------
     * Phase 5:
     *
     * Append all the args in svpv_buf, plus the const strings, to targ.
     *
     * On entry to this section the (pv,len) pairs in svpv_buf have the
     * following meanings:
     *    (pv,  len)         a pure-plain or utf8 string (which may be targ)
     *    (pv, -(len+extra)) a plain string which will expand by 'extra'
     *                         bytes when converted to utf8
     *    (0,  -len)         left-most targ, whose content has already
     *                         been copied. Just advance targ_pv by len.
     */

    /* If there are no constant strings and no special case args
     * (svpv_p->len < 0), use a simpler, more efficient concat loop
     */
    if (!slow_concat) {
        for (svpv_p = svpv_base; svpv_p < svpv_end; svpv_p++) {
            SSize_t len = svpv_p->len;
            if (!len)
                continue;
            Copy(svpv_p->pv, targ_pv, len, char);
            targ_pv += len;
        }
    }
    else {
        /* Note that we iterate the loop nargs+1 times: to append nargs
         * arguments and nargs+1 constant strings. For example, "-$a-$b-"
         */
        svpv_p = svpv_base;

        for (;;) {
            SSize_t len = (const_lens++)->ssize;

            /* append next const string segment */
            if (len > 0) {
                Copy(const_pv, targ_pv, len, char);
                targ_pv   += len;
                const_pv += len;
            }

            if (svpv_p == svpv_end)
                break;

            /* append next arg */
            len = svpv_p->len;

            if (LIKELY(len > 0)) {
                Copy(svpv_p->pv, targ_pv, len, char);
                targ_pv += len;
            }
            else if (UNLIKELY(len < 0)) {
                /* negative length indicates two special cases */
                const char *p = svpv_p->pv;
                len = -len;
                if (UNLIKELY(p)) {
                    /* copy plain-but-variant pv to a utf8 targ */
                    char * end_pv = targ_pv + len;
                    assert(dst_utf8);
                    while (targ_pv < end_pv) {
                        U8 c = (U8) *p++;
                        append_utf8_from_native_byte(c, (U8**)&targ_pv);
                    }
                }
                else
                    /* arg is already-copied targ */
                    targ_pv += len;
            }

            ++svpv_p;
        }
    }

    *targ_pv = '\0';
    SvCUR_set(targ, targ_pv - SvPVX(targ));
    assert(grow >= SvCUR(targ) + 1);
    assert(SvLEN(targ) >= SvCUR(targ) + 1);

    /* --------------------------------------------------------------
     * Phase 6:
     *
     * return result
     */

    rpp_popfree_to_NN(PL_stack_sp - stack_adj);
    SvTAINT(targ);
    SvSETMAGIC(targ);
    rpp_push_1(targ);
    return NORMAL;

    /* --------------------------------------------------------------
     * Phase 7:
     *
     * We only get here if any of the args (or targ too in the case of
     * append) have something which might cause side effects, such
     * as magic, overload, or an undef value in the presence of warnings.
     * In that case, any earlier attempt to stringify the args will have
     * been abandoned, and we come here instead.
     *
     * Here, we concat each arg in turn the old-fashioned way: essentially
     * emulating pp_concat() in a loop. This means that all the weird edge
     * cases will be handled correctly, if not necessarily speedily.
     *
     * Note that some args may already have been stringified - those are
     * processed again, which is safe, since only args without side-effects
     * were stringified earlier.
     */

  do_magical:
    {
        SSize_t i, n;
        SV *left = NULL;
        SV *right;
        SV* nexttarg;
        bool nextappend;
        U32 utf8 = 0;
        SV **svp;
        const char    *cpv  = aux[PERL_MULTICONCAT_IX_PLAIN_PV].pv;
        SV            *csv  = NULL; /* SV which will hold cpv */
        UNOP_AUX_item *lens = aux + PERL_MULTICONCAT_IX_LENGTHS;
        Size_t arg_count = 0; /* how many args have been processed */

        if (!cpv) {
            cpv = aux[PERL_MULTICONCAT_IX_UTF8_PV].pv;
            utf8 = SVf_UTF8;
        }

        svp = toparg - nargs + 1;

        /* iterate for:
         *   nargs arguments,
         *   plus possible nargs+1 consts,
         *   plus, if appending, a final targ in an extra last iteration
         */

        n = nargs *2 + 1;
        for (i = 0; i <= n; i++) {
            SSize_t len;

            /* if necessary, stringify the final RHS result in
             * something like $targ .= "$a$b$c" - simulating
             * pp_stringify
             */
            if (    i == n
                && (PL_op->op_private &OPpMULTICONCAT_STRINGIFY)
                && !(SvPOK(left))
                /* extra conditions for backwards compatibility:
                 * probably incorrect, but keep the existing behaviour
                 * for now. The rules are:
                 *     $x   = "$ov"     single arg: stringify;
                 *     $x   = "$ov$y"   multiple args: don't stringify,
                 *     $lex = "$ov$y$z" except TARGMY with at least 2 concats
                 */
                && (   arg_count == 1
                    || (     arg_count >= 3
                        && !is_append
                        &&  (PL_op->op_private & OPpTARGET_MY)
                        && !(PL_op->op_private & OPpLVAL_INTRO)
                       )
                   )
            )
            {
                assert(aux[PERL_MULTICONCAT_IX_PADTMP2].pad_offset);
                SV *tmp = PAD_SV(aux[PERL_MULTICONCAT_IX_PADTMP2].pad_offset);
                sv_copypv(tmp, left);
                SvSETMAGIC(tmp);
                left = tmp;
            }

            /* do one extra iteration to handle $targ in $targ .= ... */
            if (i == n && !is_append)
                break;

            /* get the next arg SV or regen the next const SV */
            len = lens[i >> 1].ssize;
            if (i == n) {
                /* handle the final targ .= (....) */
                right = left;
                left = targ;
            }
            else if (i & 1)
                right = svp[(i >> 1)];
            else if (len < 0)
                continue; /* no const in this position */
            else {
                /* Use one of our PADTMPs to fake up the SV which would
                 * have been returned by an OP_CONST.  Try to reuse it if
                 * possible. If the refcount has gone up, something like
                 * overload code has taken a reference to it, so abandon
                 * it */
                if (!csv || SvREFCNT(csv) > 1 || SvLEN(csv) != 0) {
                    if (csv)
                        csv = newSV_type_mortal(SVt_PV);
                    else {
                        assert(aux[PERL_MULTICONCAT_IX_PADTMP1].pad_offset);
                        csv = PAD_SV(
                                aux[PERL_MULTICONCAT_IX_PADTMP1].pad_offset);
                        SvUPGRADE(csv, SVt_PV);
                    }

                    if (utf8)
                        SvUTF8_on(csv);
                    SvREADONLY_on(csv);
                    SvPOK_on(csv);
                }
                /* use the const string buffer directly with the
                 * SvLEN==0 trick */

                /* cast away constness because we think we know it's safe
                 * (SvREADONLY) */
                SvPV_set(csv, (char *)cpv);
                SvLEN_set(csv, 0);
                SvCUR_set(csv, len);

                right = csv;
                cpv += len;
            }

            arg_count++;

            if (arg_count <= 1) {
                left = right;
                continue; /* need at least two SVs to concat together */
            }

            if (arg_count == 2 && i < n) {
                /* for the first concat, use one of the PADTMPs to emulate
                 * the PADTMP from OP_CONST. In later iterations this will
                 * be appended to */
                nexttarg = PAD_SV(aux[PERL_MULTICONCAT_IX_PADTMP0].pad_offset);
                nextappend = FALSE;
            }
            else {
                nexttarg = left;
                nextappend = TRUE;
            }

            /* Handle possible overloading.
             * This is basically an unrolled
             *     tryAMAGICbin_MG(concat_amg, AMGf_assign);
             * and
             *     Perl_try_amagic_bin()
             * call, but using left and right rather than
             * PL_stack_sp[-1], PL_stack_sp[0],
             * and not relying on OPf_STACKED implying .=
             */

            if ((SvFLAGS(left)|SvFLAGS(right)) & (SVf_ROK|SVs_GMG)) {
                SvGETMAGIC(left);
                if (left != right)
                    SvGETMAGIC(right);

                if ((SvAMAGIC(left) || SvAMAGIC(right))
                    /* sprintf doesn't do concat overloading,
                     * but allow for $x .= sprintf(...)
                     */
                    && (   !(PL_op->op_private & OPpMULTICONCAT_FAKE)
                        || i == n)
                    )
                {
                    SV * const tmpsv = amagic_call(left, right, concat_amg,
                                                (nextappend ? AMGf_assign: 0));
                    if (tmpsv) {
                        /* NB: tryAMAGICbin_MG() includes an OPpTARGET_MY test
                         * here, which isn't needed as any implicit
                         * assign done under OPpTARGET_MY is done after
                         * this loop */
                        if (nextappend) {
                            sv_setsv(left, tmpsv);
                            SvSETMAGIC(left);
                        }
                        else
                            left = tmpsv;
                        continue;
                    }
                }

                /* if both args are the same magical value, make one a copy */
                if (left == right && SvGMAGICAL(left)) {
                    SV * targetsv = right;
                    /* Print the uninitialized warning now, so it includes the
                     * variable name. */
                    if (!SvOK(right)) {
                        if (ckWARN(WARN_UNINITIALIZED))
                            report_uninit(right);
                        targetsv = &PL_sv_no;
                    }
                    left = sv_mortalcopy_flags(targetsv, 0);
                    SvGETMAGIC(right);
                }
            }

            /* nexttarg = left . right */
            S_do_concat(aTHX_ left, right, nexttarg, 0);
            left = nexttarg;
        }

        /* Return the result of all RHS concats, unless this op includes
         * an assign ($lex = x.y.z or expr = x.y.z), in which case copy
         * to target (which will be $lex or expr).
         * If we are appending, targ will already have been appended to in
         * the loop */
        if (  !is_append
            && (   (PL_op->op_flags   & OPf_STACKED)
                || (PL_op->op_private & OPpTARGET_MY))
        ) {
            sv_setsv(targ, left);
            SvSETMAGIC(targ);
        }
        else
            targ = left;

        rpp_popfree_to_NN(PL_stack_sp - stack_adj);
        rpp_push_1(targ);
        return NORMAL;
    }
}


/* push the elements of av onto the stack.
 * Returns PL_op->op_next to allow tail-call optimisation of its callers */

STATIC OP*
S_pushav(pTHX_ AV* const av)
{
    const SSize_t maxarg = AvFILL(av) + 1;
    rpp_extend(maxarg);
    if (UNLIKELY(SvRMAGICAL(av))) {
        PADOFFSET i;
        for (i=0; i < (PADOFFSET)maxarg; i++) {
            SV ** const svp = av_fetch(av, i, FALSE);
            rpp_push_1(LIKELY(svp)
                       ? *svp
                       : UNLIKELY(PL_op->op_flags & OPf_MOD)
                          ? av_nonelem(av,i)
                          : &PL_sv_undef
            );
        }
    }
    else {
        PADOFFSET i;
        for (i=0; i < (PADOFFSET)maxarg; i++) {
            SV *sv = AvARRAY(av)[i];
            rpp_push_1(LIKELY(sv)
                       ? sv
                       : UNLIKELY(PL_op->op_flags & OPf_MOD)
                          ? av_nonelem(av,i)
                          : &PL_sv_undef
            );
        }
    }
    return NORMAL;
}


/* ($lex1,@lex2,...)   or my ($lex1,@lex2,...)  */

PP(pp_padrange)
{
    PADOFFSET base = PL_op->op_targ;
    int count = (int)(PL_op->op_private) & OPpPADRANGE_COUNTMASK;
    if (PL_op->op_flags & OPf_SPECIAL) {
        /* fake the RHS of my ($x,$y,..) = @_ */
        PUSHMARK(PL_stack_sp);
        (void)S_pushav(aTHX_ GvAVn(PL_defgv));
    }

    /* note, this is only skipped for compile-time-known void cxt */
    if ((PL_op->op_flags & OPf_WANT) != OPf_WANT_VOID) {
        int i;

        rpp_extend(count);
        PUSHMARK(PL_stack_sp);
        for (i = 0; i <count; i++)
            rpp_push_1(PAD_SV(base+i));
    }

    if (PL_op->op_private & OPpLVAL_INTRO) {
        SV **svp = &(PAD_SVl(base));
        const UV payload = (UV)(
                      (base << (OPpPADRANGE_COUNTSHIFT + SAVE_TIGHT_SHIFT))
                    | (count << SAVE_TIGHT_SHIFT)
                    | SAVEt_CLEARPADRANGE);
        int i;

        STATIC_ASSERT_STMT(OPpPADRANGE_COUNTMASK + 1 == (1 << OPpPADRANGE_COUNTSHIFT));
        assert((payload >> (OPpPADRANGE_COUNTSHIFT+SAVE_TIGHT_SHIFT))
                == (Size_t)base);
        {
            dSS_ADD;
            SS_ADD_UV(payload);
            SS_ADD_END(1);
        }

        for (i = 0; i <count; i++)
            SvPADSTALE_off(*svp++); /* mark lexical as active */
    }
    return NORMAL;
}


PP(pp_padsv)
{
    {
        OP * const op = PL_op;
        /* access PL_curpad once */
        SV ** const padentry = &(PAD_SVl(op->op_targ));
        {
            dTARG;
            TARG = *padentry;
            rpp_xpush_1(TARG);
        }
        if (op->op_flags & OPf_MOD) {
            if (op->op_private & OPpLVAL_INTRO)
                if (!(op->op_private & OPpPAD_STATE))
                    save_clearsv(padentry);
            if (op->op_private & OPpDEREF) {
                /* *sp is equivalent to TARG here.  Using *sp rather
                   than TARG reduces the scope of TARG, so it does not
                   span the call to save_clearsv, resulting in smaller
                   machine code. */
                rpp_replace_1_1_NN(
                    vivify_ref(*PL_stack_sp, op->op_private & OPpDEREF));
            }
        }
        return op->op_next;
    }
}


/* Implement readline(), and also <X> and <<X>> in the cases where X is
 * seen by the parser as file-handle-ish rather than glob-ish.
 *
 * It expects at least one arg: the typeglob or scalar filehandle to read
 * from. An empty <> isn't handled specially by this op; instead the parser
 * will have planted a preceding gv(*ARGV) op.
 *
 * Scalar assignment is optimised away by making the assignment target be
 * passed as a second argument, with OPf_STACKED set. For example,
 *
 *    $x[$i] = readline($fh);
 *
 * is implemented as if written as
 *
 *    readline($x[$i], $fh);
 *
 * (that is, if the perl-level readline function took two args, which it
 * doesn't). The 'while (<>) {...}' construct is handled specially by the
 * parser, but not specially by this op. The parser treats the condition
 * as
 *
 *    defined($_ = <>)
 *
 * which is then optimised into the equivalent of
 *
 *   defined(readline($_, *ARGV))
 *
 * When called as a real function, e.g. (\&CORE::readline)->(*STDIN),
 * pp_coreargs() will have pushed a NULL if no argument was supplied.
 *
 * The parser decides whether '<something>' in the perl src code causes an
 * OP_GLOB or an OP_READLINE op to be planted.
 */

PP(pp_readline)
{
    SV *arg = *PL_stack_sp;

    /* pp_coreargs pushes a NULL to indicate no args passed to
     * CORE::readline() */
    if (arg) {
        SvGETMAGIC(arg);

        /* unrolled tryAMAGICunTARGETlist(iter_amg, 0) */
        SV *tmpsv;
        U8 gimme = GIMME_V;
        if (UNLIKELY(SvAMAGIC(arg) &&
            (tmpsv = amagic_call(arg, &PL_sv_undef, iter_amg,
                                 AMGf_want_list | AMGf_noright
                                |AMGf_unary))))
        {
            if (gimme == G_VOID) {
                NOOP;
            }
            else if (gimme == G_LIST) {
                SSize_t i;
                SSize_t len;
                assert(SvTYPE(tmpsv) == SVt_PVAV);
                len = av_count((AV *)tmpsv);
                assert(*PL_stack_sp == arg);
                rpp_popfree_1_NN(); /* pop the original filehhandle arg */
                /* no assignment target to pop */
                assert(!(PL_op->op_flags & OPf_STACKED));
                rpp_extend(len);
                for (i = 0; i < len; ++i)
                    /* amagic_call() naughtily doesn't increment the ref counts
                     * of the items it pushes onto the temporary array. So we
                     * don't need to decrement them when shifting off. */
                    rpp_push_1(av_shift((AV *)tmpsv));
            }
            else { /* AMGf_want_scalar */
                /* OPf_STACKED: assignment optimised away and target
                 * on stack */
                SV *targ = (PL_op->op_flags & OPf_STACKED)
                                ? PL_stack_sp[-1]
                                : PAD_SV(PL_op->op_targ);
                sv_setsv(targ, tmpsv);
                SvSETMAGIC(targ);
                if (PL_op->op_flags & OPf_STACKED) {
                    rpp_popfree_1_NN();
                    assert(*PL_stack_sp == targ);
                }
                else
                    rpp_replace_1_1_NN(targ);
            }
            return NORMAL;
        }
        /* end of unrolled tryAMAGICunTARGETlist */

        PL_last_in_gv = MUTABLE_GV(*PL_stack_sp);
#ifdef PERL_RC_STACK
        /* PL_last_in_gv appears to be non-refcounted, so won't keep
         * GV alive */
        if (SvREFCNT(PL_last_in_gv) < 2)
            sv_2mortal((SV*)PL_last_in_gv);
#endif
        rpp_popfree_1_NN();
    }
    else {
        PL_last_in_gv = PL_argvgv;
        PL_stack_sp--;
    }


    /* is it *FOO, $fh, or 'FOO' ? */
    if (!isGV_with_GP(PL_last_in_gv)) {
        if (SvROK(PL_last_in_gv) && isGV_with_GP(SvRV(PL_last_in_gv)))
            PL_last_in_gv = GV_FROM_REF((SV *)PL_last_in_gv);
        else {
            rpp_xpush_1(MUTABLE_SV(PL_last_in_gv));
            Perl_pp_rv2gv(aTHX);
            PL_last_in_gv = MUTABLE_GV(*PL_stack_sp);
            rpp_popfree_1_NN();
            assert(   (SV*)PL_last_in_gv == &PL_sv_undef
                   || isGV_with_GP(PL_last_in_gv));
        }
    }

    return do_readline();
}


PP(pp_eq)
{
    if (rpp_try_AMAGIC_2(eq_amg, AMGf_numeric))
        return NORMAL;

    SV *right = PL_stack_sp[0];
    SV *left  = PL_stack_sp[-1];

    U32 flags_and = SvFLAGS(left) & SvFLAGS(right);
    U32 flags_or  = SvFLAGS(left) | SvFLAGS(right);

    rpp_replace_2_IMM_NN(boolSV(
        ( (flags_and & SVf_IOK) && ((flags_or & SVf_IVisUV) ==0 ) )
        ?    (SvIVX(left) == SvIVX(right))
        : (flags_and & SVf_NOK)
        ?    (SvNVX(left) == SvNVX(right))
        : ( do_ncmp(left, right) == 0)
    ));
    return NORMAL;
}


/* also used for: pp_i_preinc() */

PP(pp_preinc)
{
    SV *sv = *PL_stack_sp;

    if (LIKELY(((sv->sv_flags &
                        (SVf_THINKFIRST|SVs_GMG|SVf_IVisUV|
                         SVf_IOK|SVf_NOK|SVf_POK|SVp_NOK|SVp_POK|SVf_ROK))
                == SVf_IOK))
        && SvIVX(sv) != IV_MAX)
    {
        SvIV_set(sv, SvIVX(sv) + 1);
    }
    else /* Do all the PERL_PRESERVE_IVUV and hard cases in sv_inc */
        sv_inc(sv);
    SvSETMAGIC(sv);
    return NORMAL;
}


/* also used for: pp_i_predec() */

PP(pp_predec)
{
    SV *sv = *PL_stack_sp;

    if (LIKELY(((sv->sv_flags &
                        (SVf_THINKFIRST|SVs_GMG|SVf_IVisUV|
                         SVf_IOK|SVf_NOK|SVf_POK|SVp_NOK|SVp_POK|SVf_ROK))
                == SVf_IOK))
        && SvIVX(sv) != IV_MIN)
    {
        SvIV_set(sv, SvIVX(sv) - 1);
    }
    else /* Do all the PERL_PRESERVE_IVUV and hard cases  in sv_dec */
        sv_dec(sv);
    SvSETMAGIC(sv);
    return NORMAL;
}


/* also used for: pp_orassign() */

PP(pp_or)
{
    SV *sv;
    PERL_ASYNC_CHECK();
    sv = *PL_stack_sp;
    if (SvTRUE_NN(sv))
        return NORMAL;
    else {
        if (PL_op->op_type == OP_OR)
            rpp_popfree_1_NN();
        return cLOGOP->op_other;
    }
}


/* also used for: pp_dor() pp_dorassign() */

PP(pp_defined)
{
    SV* sv = *PL_stack_sp;
    bool defined = FALSE;
    const int op_type = PL_op->op_type;
    const bool is_dor = (op_type == OP_DOR || op_type == OP_DORASSIGN);

    if (is_dor) {
        PERL_ASYNC_CHECK();
        if (UNLIKELY(!sv || !SvANY(sv))) {
            if (op_type == OP_DOR)
                rpp_popfree_1();
            return cLOGOP->op_other;
        }
    }
    else {
        /* OP_DEFINED */
        if (UNLIKELY(!sv || !SvANY(sv))) {
            rpp_replace_1_1(&PL_sv_no);
            return NORMAL;
        }
    }

    /* Historically what followed was a switch on SvTYPE(sv), handling SVt_PVAV,
     * SVt_PVCV, SVt_PVHV and "default". `defined &sub` is still valid syntax,
     * hence we still need the special case PVCV code. But AVs and HVs now
     * should never arrive here... */
#ifdef DEBUGGING
    assert(SvTYPE(sv) != SVt_PVAV);
    assert(SvTYPE(sv) != SVt_PVHV);
#endif

    if (UNLIKELY(SvTYPE(sv) == SVt_PVCV)) {
        if (CvROOT(sv) || CvXSUB(sv))
            defined = TRUE;
    }
    else {
        SvGETMAGIC(sv);
        if (SvOK(sv))
            defined = TRUE;
    }

    if (is_dor) {
        if(defined) 
            return NORMAL;
        if(op_type == OP_DOR)
            rpp_popfree_1_NN();
        return cLOGOP->op_other;
    }
    /* assuming OP_DEFINED */
    rpp_replace_1_IMM_NN(defined ? &PL_sv_yes : &PL_sv_no);
    return NORMAL;
}



PP(pp_add)
{
    bool useleft; SV *svl, *svr;
    SV *targ = (PL_op->op_flags & OPf_STACKED)
                    ? PL_stack_sp[-1]
                    : PAD_SV(PL_op->op_targ);

    if (rpp_try_AMAGIC_2(add_amg, AMGf_assign|AMGf_numeric))
        return NORMAL;

    svr = PL_stack_sp[0];
    svl = PL_stack_sp[-1];

#ifdef PERL_PRESERVE_IVUV

    /* special-case some simple common cases */
    if (!((svl->sv_flags|svr->sv_flags) & (SVf_IVisUV|SVs_GMG))) {
        IV il, ir;
        U32 flags = (svl->sv_flags & svr->sv_flags);
        if (flags & SVf_IOK) {
            /* both args are simple IVs */
            UV topl, topr;
            il = SvIVX(svl);
            ir = SvIVX(svr);
          do_iv:
            topl = ((UV)il) >> (UVSIZE * 8 - 2);
            topr = ((UV)ir) >> (UVSIZE * 8 - 2);

            /* if both are in a range that can't under/overflow, do a
             * simple integer add: if the top of both numbers
             * are 00  or 11, then it's safe */
            if (!( ((topl+1) | (topr+1)) & 2)) {
                TARGi(il + ir, 0); /* args not GMG, so can't be tainted */
                goto ret;
            }
            goto generic;
        }
        else if (flags & SVf_NOK) {
            /* both args are NVs */
            NV nl = SvNVX(svl);
            NV nr = SvNVX(svr);

            if (lossless_NV_to_IV(nl, &il) && lossless_NV_to_IV(nr, &ir)) {
                /* nothing was lost by converting to IVs */
                goto do_iv;
            }
            TARGn(nl + nr, 0); /* args not GMG, so can't be tainted */
            goto ret;
        }
    }

  generic:

    useleft = USE_LEFT(svl);
    /* We must see if we can perform the addition with integers if possible,
       as the integer code detects overflow while the NV code doesn't.
       If either argument hasn't had a numeric conversion yet attempt to get
       the IV. It's important to do this now, rather than just assuming that
       it's not IOK as a PV of "9223372036854775806" may not take well to NV
       addition, and an SV which is NOK, NV=6.0 ought to be coerced to
       integer in case the second argument is IV=9223372036854775806
       We can (now) rely on sv_2iv to do the right thing, only setting the
       public IOK flag if the value in the NV (or PV) slot is truly integer.

       A side effect is that this also aggressively prefers integer maths over
       fp maths for integer values.

       How to detect overflow?

       C 99 section 6.2.6.1 says

       The range of nonnegative values of a signed integer type is a subrange
       of the corresponding unsigned integer type, and the representation of
       the same value in each type is the same. A computation involving
       unsigned operands can never overflow, because a result that cannot be
       represented by the resulting unsigned integer type is reduced modulo
       the number that is one greater than the largest value that can be
       represented by the resulting type.

       (the 9th paragraph)

       which I read as "unsigned ints wrap."

       signed integer overflow seems to be classed as "exception condition"

       If an exceptional condition occurs during the evaluation of an
       expression (that is, if the result is not mathematically defined or not
       in the range of representable values for its type), the behavior is
       undefined.

       (6.5, the 5th paragraph)

       I had assumed that on 2s complement machines signed arithmetic would
       wrap, hence coded pp_add and pp_subtract on the assumption that
       everything perl builds on would be happy.  After much wailing and
       gnashing of teeth it would seem that irix64 knows its ANSI spec well,
       knows that it doesn't need to, and doesn't.  Bah.  Anyway, the all-
       unsigned code below is actually shorter than the old code. :-)
    */

    if (SvIV_please_nomg(svr)) {
        /* Unless the left argument is integer in range we are going to have to
           use NV maths. Hence only attempt to coerce the right argument if
           we know the left is integer.  */
        UV auv = 0;
        bool auvok = FALSE;
        bool a_valid = 0;

        if (!useleft) {
            auv = 0;
            a_valid = auvok = 1;
            /* left operand is undef, treat as zero. + 0 is identity,
               Could TARGi or TARGu right now, but space optimise by not
               adding lots of code to speed up what is probably a rare-ish
               case. */
        } else {
            /* Left operand is defined, so is it IV? */
            if (SvIV_please_nomg(svl)) {
                if ((auvok = SvUOK(svl)))
                    auv = SvUVX(svl);
                else {
                    const IV aiv = SvIVX(svl);
                    if (aiv >= 0) {
                        auv = aiv;
                        auvok = 1;	/* Now acting as a sign flag.  */
                    } else {
                        auv = NEGATE_2UV(aiv);
                    }
                }
                a_valid = 1;
            }
        }
        if (a_valid) {
            bool result_good = 0;
            UV result;
            UV buv;
            bool buvok = SvUOK(svr);
        
            if (buvok)
                buv = SvUVX(svr);
            else {
                const IV biv = SvIVX(svr);
                if (biv >= 0) {
                    buv = biv;
                    buvok = 1;
                } else
                    buv = NEGATE_2UV(biv);
            }
            /* ?uvok if value is >= 0. basically, flagged as UV if it's +ve,
               else "IV" now, independent of how it came in.
               if a, b represents positive, A, B negative, a maps to -A etc
               a + b =>  (a + b)
               A + b => -(a - b)
               a + B =>  (a - b)
               A + B => -(a + b)
               all UV maths. negate result if A negative.
               add if signs same, subtract if signs differ. */

            if (auvok ^ buvok) {
                /* Signs differ.  */
                if (auv >= buv) {
                    result = auv - buv;
                    /* Must get smaller */
                    if (result <= auv)
                        result_good = 1;
                } else {
                    result = buv - auv;
                    if (result <= buv) {
                        /* result really should be -(auv-buv). as its negation
                           of true value, need to swap our result flag  */
                        auvok = !auvok;
                        result_good = 1;
                    }
                }
            } else {
                /* Signs same */
                result = auv + buv;
                if (result >= auv)
                    result_good = 1;
            }
            if (result_good) {
                if (auvok)
                    TARGu(result,1);
                else {
                    /* Negate result */
                    if (result <= ABS_IV_MIN)
                        TARGi(NEGATE_2IV(result), 1);
                    else {
                        /* result valid, but out of range for IV.  */
                        TARGn(-(NV)result, 1);
                    }
                }
                goto ret;
            } /* Overflow, drop through to NVs.  */
        }
    }

#else
    useleft = USE_LEFT(svl);
#endif

    {
        NV value = SvNV_nomg(svr);
        if (!useleft) {
            /* left operand is undef, treat as zero. + 0.0 is identity. */
            TARGn(value, 1);
        }
        else {
            TARGn(value + SvNV_nomg(svl), 1);
        }
    }

  ret:
    rpp_replace_2_1_NN(targ);
    return NORMAL;
}


/* also used for: pp_aelemfast_lex() */

PP(pp_aelemfast)
{
    AV * const av = PL_op->op_type == OP_AELEMFAST_LEX
        ? MUTABLE_AV(PAD_SV(PL_op->op_targ)) : GvAVn(cGVOP_gv);
    const U32 lval = PL_op->op_flags & OPf_MOD;
    const I8 key   = (I8)PL_op->op_private;
    SV** svp;
    SV *sv;

    assert(SvTYPE(av) == SVt_PVAV);

    /* inlined av_fetch() for simple cases ... */
    if (!SvRMAGICAL(av) && key >= 0 && key <= AvFILLp(av)) {
        sv = AvARRAY(av)[key];
        if (sv)
            goto ret;
        if (!lval) {
            sv = &PL_sv_undef;
            goto ret;
        }
    }

    /* ... else do it the hard way */
    svp = av_fetch(av, key, lval);
    sv = (svp ? *svp : &PL_sv_undef);

    if (UNLIKELY(!svp && lval))
        DIE(aTHX_ PL_no_aelem, (int)key);

    if (!lval && SvRMAGICAL(av) && SvGMAGICAL(sv)) /* see note in pp_helem() */
        mg_get(sv);

  ret:
    rpp_xpush_1(sv);
    return NORMAL;
}

PP(pp_join)
{
    dMARK; dTARGET;
    MARK++;
    do_join(TARG, *MARK, MARK, PL_stack_sp);
    rpp_popfree_to_NN(MARK - 1);
    rpp_push_1(TARG);
    return NORMAL;
}


/* Oversized hot code. */

/* also used for: pp_say() */

PP(pp_print)
{
    dMARK; dORIGMARK;
    PerlIO *fp;
    MAGIC *mg;
    GV * const gv
        = (PL_op->op_flags & OPf_STACKED) ? MUTABLE_GV(*++MARK) : PL_defoutgv;
    IO *io = GvIO(gv);
    SV *retval = &PL_sv_undef;

    if (io
        && (mg = SvTIED_mg((const SV *)io, PERL_MAGIC_tiedscalar)))
    {
      had_magic:
        if (MARK == ORIGMARK) {
            /* If using default handle then we need to make space to
             * pass object as 1st arg, so move other args up ...
             */
            rpp_extend(1);
            MARK = ORIGMARK; /* stack may have been realloced */
            ++MARK;
            Move(MARK, MARK + 1, (PL_stack_sp - MARK) + 1, SV*);
            *MARK = NULL;
            ++PL_stack_sp;
        }
        return Perl_tied_method(aTHX_ SV_CONST(PRINT), mark - 1, MUTABLE_SV(io),
                                mg,
                                (G_SCALAR | TIED_METHOD_ARGUMENTS_ON_STACK
                                 | (PL_op->op_type == OP_SAY
                                    ? TIED_METHOD_SAY : 0)),
                                PL_stack_sp - mark);
    }

    if (!io) {
        if ( gv && GvEGVx(gv) && (io = GvIO(GvEGV(gv)))
            && (mg = SvTIED_mg((const SV *)io, PERL_MAGIC_tiedscalar)))
            goto had_magic;
        report_evil_fh(gv);
        SETERRNO(EBADF,RMS_IFI);
        goto just_say_no;
    }
    else if (!(fp = IoOFP(io))) {
        if (IoIFP(io))
            report_wrongway_fh(gv, '<');
        else
            report_evil_fh(gv);
        SETERRNO(EBADF,IoIFP(io)?RMS_FAC:RMS_IFI);
        goto just_say_no;
    }
    else {
        SV * const ofs = GvSV(PL_ofsgv); /* $, */
        MARK++;
        if (ofs && (SvGMAGICAL(ofs) || SvOK(ofs))) {
            while (MARK <= PL_stack_sp) {
                if (!do_print(*MARK, fp))
                    break;
                MARK++;
                if (MARK <= PL_stack_sp) {
                    /* don't use 'ofs' here - it may be invalidated by magic callbacks */
                    if (!do_print(GvSV(PL_ofsgv), fp)) {
                        MARK--;
                        break;
                    }
                }
            }
        }
        else {
            while (MARK <= PL_stack_sp) {
                if (!do_print(*MARK, fp))
                    break;
                MARK++;
            }
        }
        if (MARK <= PL_stack_sp)
            goto just_say_no;
        else {
            if (PL_op->op_type == OP_SAY) {
                if (PerlIO_write(fp, "\n", 1) == 0 || PerlIO_error(fp))
                    goto just_say_no;
            }
            else if (PL_ors_sv && SvOK(PL_ors_sv))
                if (!do_print(PL_ors_sv, fp)) /* $\ */
                    goto just_say_no;

            if (IoFLAGS(io) & IOf_FLUSH)
                if (PerlIO_flush(fp) == EOF)
                    goto just_say_no;
        }
    }
    retval = &PL_sv_yes;

  just_say_no:
    rpp_popfree_to_NN(ORIGMARK);
    if ((PL_op->op_flags & OPf_WANT) != OPf_WANT_VOID)
        rpp_xpush_IMM(retval);
    return NORMAL;
}


/* do the common parts of pp_padhv() and pp_rv2hv()
 * It assumes the caller has done rpp_extend(1) or equivalent.
 * 'is_keys' indicates the OPpPADHV_ISKEYS/OPpRV2HV_ISKEYS flag is set.
 * 'has_targ' indicates that the op has a target - this should
 * be a compile-time constant so that the code can constant-folded as
 * appropriate. has_targ also implies that the caller has left an
 * arg on the stack which needs freeing.
 * */

PERL_STATIC_INLINE OP*
S_padhv_rv2hv_common(pTHX_ HV *hv, U8 gimme, bool is_keys, bool has_targ)
{
    assert(PL_op->op_type == OP_PADHV || PL_op->op_type == OP_RV2HV);

    if (gimme == G_LIST) {
        /* push all (key,value) pairs onto stack */
        if (has_targ) { /* i.e. if has arg still on stack */
#ifdef PERL_RC_STACK
            SSize_t sp_base = PL_stack_sp - PL_stack_base;
            hv_pushkv(hv, 3);
            /* Now safe to free the original arg on the stack and shuffle
             * down one place anything pushed on top of it */
            SSize_t nitems = PL_stack_sp - (PL_stack_base + sp_base);
            SV *old_sv = PL_stack_sp[-nitems];
            if (nitems)
                Move(PL_stack_sp - nitems + 1,
                     PL_stack_sp - nitems,    nitems, SV*);
            PL_stack_sp--;
            SvREFCNT_dec_NN(old_sv);
#else
            rpp_popfree_1_NN();
            hv_pushkv(hv, 3);
#endif
        }
        else
            hv_pushkv(hv, 3);
        return NORMAL;
    }

    if (is_keys)
        /* 'keys %h' masquerading as '%h': reset iterator */
        (void)hv_iterinit(hv);

    if (gimme == G_VOID) {
        if (has_targ)
            rpp_popfree_1_NN();
        return NORMAL;
    }

    bool is_bool = (     PL_op->op_private & OPpTRUEBOOL
                   || (  PL_op->op_private & OPpMAYBE_TRUEBOOL
                      && block_gimme() == G_VOID));

    MAGIC *is_tied_mg = SvRMAGICAL(hv)
                        ? mg_find(MUTABLE_SV(hv), PERL_MAGIC_tied)
                        : NULL;

    IV  i = 0;
    SV *sv = NULL;
    if (UNLIKELY(is_tied_mg)) {
        if (is_keys && !is_bool) {
            i = 0;
            while (hv_iternext(hv))
                i++;
            /* hv finished with. Safe to free arg now */
            if (has_targ)
                rpp_popfree_1_NN();
            goto push_i;
        }
        else {
            sv = magic_scalarpack(hv, is_tied_mg);
            /* hv finished with. Safe to free arg now */
            if (has_targ)
                rpp_popfree_1_NN();
            rpp_push_1(sv);
        }
    }
    else {
#if defined(DYNAMIC_ENV_FETCH) && defined(VMS)
        /* maybe nothing set up %ENV for iteration yet...
           do this always (not just if HvUSEDKEYS(hv) is currently 0) because
           we ought to give a *consistent* answer to "how many keys?"
           whether we ask this op in scalar context, or get the list of all
           keys then check its length, and whether we do either with or without
           an %ENV lookup first. prime_env_iter() returns quickly if nothing
           needs doing. */
        if (SvRMAGICAL((const SV *)hv)
            && mg_find((const SV *)hv, PERL_MAGIC_env)) {
            prime_env_iter();
        }
#endif
        i = HvUSEDKEYS(hv);

        /* hv finished with. Safe to free arg now */
        if (has_targ)
            rpp_popfree_1_NN();

        if (is_bool) {
            rpp_push_IMM(i ? &PL_sv_yes : &PL_sv_zero);
        }
        else {
          push_i:
            if (has_targ) {
                dTARGET;
                TARGi(i,1);
                rpp_push_1(targ);
            }
            else
            if (is_keys) {
                /* parent op should be an unused OP_KEYS whose targ we can
                 * use */
                dTARG;
                OP *k;

                assert(!OpHAS_SIBLING(PL_op));
                k = PL_op->op_sibparent;
                assert(k->op_type == OP_KEYS);
                TARG = PAD_SV(k->op_targ);
                TARGi(i,1);
                rpp_push_1(targ);
            }
            else
                rpp_push_1_norc(newSViv(i));
        }
    }

    return NORMAL;
}


/* This is also called directly by pp_lvavref.  */
PP(pp_padav)
{
    dTARGET;
    U8 gimme;

    assert(SvTYPE(TARG) == SVt_PVAV);
    if (UNLIKELY( PL_op->op_private & OPpLVAL_INTRO ))
        if (LIKELY( !(PL_op->op_private & OPpPAD_STATE) ))
            SAVECLEARSV(PAD_SVl(PL_op->op_targ));


    if (PL_op->op_flags & OPf_REF)
        goto ret;

    if (PL_op->op_private & OPpMAYBE_LVSUB) {
        const I32 flags = is_lvalue_sub();
        if (flags && !(flags & OPpENTERSUB_INARGS)) {
            if (GIMME_V == G_SCALAR)
                /* diag_listed_as: Can't return %s to lvalue scalar context */
                croak("Can't return array to lvalue scalar context");
            goto ret;
       }
    }

    gimme = GIMME_V;
    if (gimme == G_LIST)
        return S_pushav(aTHX_ (AV*)TARG);

    if (gimme == G_VOID)
        return NORMAL;

    {
        const SSize_t maxarg = AvFILL(MUTABLE_AV(TARG)) + 1;
        rpp_extend(1);
        if (!maxarg)
            targ = &PL_sv_zero;
        else if (PL_op->op_private & OPpTRUEBOOL)
            targ = &PL_sv_yes;
        else {
            rpp_push_1_norc(newSViv(maxarg));
            return NORMAL;
        }
        rpp_push_IMM(targ);
        return NORMAL;
    }

  ret:
    rpp_xpush_1(targ);
    return NORMAL;
}


PP(pp_padhv)
{
    dTARGET;
    U8 gimme;

    assert(SvTYPE(TARG) == SVt_PVHV);
    if (UNLIKELY( PL_op->op_private & OPpLVAL_INTRO ))
        if (LIKELY( !(PL_op->op_private & OPpPAD_STATE) ))
            SAVECLEARSV(PAD_SVl(PL_op->op_targ));

    rpp_extend(1);

    if (PL_op->op_flags & OPf_REF) {
        rpp_push_1(TARG);
        return NORMAL;
    }
    else if (PL_op->op_private & OPpMAYBE_LVSUB) {
        const I32 flags = is_lvalue_sub();
        if (flags && !(flags & OPpENTERSUB_INARGS)) {
            if (GIMME_V == G_SCALAR)
                /* diag_listed_as: Can't return %s to lvalue scalar context */
                croak("Can't return hash to lvalue scalar context");
            rpp_push_1(TARG);
            return NORMAL;
        }
    }

    gimme = GIMME_V;

    return S_padhv_rv2hv_common(aTHX_ (HV*)TARG, gimme,
                        cBOOL(PL_op->op_private & OPpPADHV_ISKEYS),
                        0 /* has_targ*/);
}


/* also used for: pp_rv2hv() */
/* also called directly by pp_lvavref */

PP(pp_rv2av)
{
    SV *sv = *PL_stack_sp;
    const U8 gimme = GIMME_V;
    static const char an_array[] = "an ARRAY";
    static const char a_hash[] = "a HASH";
    const bool is_pp_rv2av = PL_op->op_type == OP_RV2AV
                          || PL_op->op_type == OP_LVAVREF;
    const svtype type = is_pp_rv2av ? SVt_PVAV : SVt_PVHV;

    SvGETMAGIC(sv);
    if (SvROK(sv)) {
        if (UNLIKELY(SvAMAGIC(sv))) {
            sv = amagic_deref_call(sv, is_pp_rv2av ? to_av_amg : to_hv_amg);
        }
        sv = SvRV(sv);
        if (UNLIKELY(SvTYPE(sv) != type))
            /* diag_listed_as: Not an ARRAY reference */
            DIE(aTHX_ "Not %s reference", is_pp_rv2av ? an_array : a_hash);
        else if (UNLIKELY(PL_op->op_flags & OPf_MOD
                && PL_op->op_private & OPpLVAL_INTRO))
            croak("%s", PL_no_localize_ref);
    }
    else if (UNLIKELY(SvTYPE(sv) != type)) {
            GV *gv;
        
            if (!isGV_with_GP(sv)) {
                gv = Perl_softref2xv(aTHX_ sv, is_pp_rv2av ? an_array : a_hash,
                                     type);
                if (!gv)
                    return NORMAL;
            }
            else {
                gv = MUTABLE_GV(sv);
            }
            sv = is_pp_rv2av ? MUTABLE_SV(GvAVn(gv)) : MUTABLE_SV(GvHVn(gv));
            if (PL_op->op_private & OPpLVAL_INTRO)
                sv = is_pp_rv2av ? MUTABLE_SV(save_ary(gv)) : MUTABLE_SV(save_hash(gv));
    }
    if (PL_op->op_flags & OPf_REF) {
        rpp_replace_1_1_NN(sv);
        return NORMAL;
    }
    else if (UNLIKELY(PL_op->op_private & OPpMAYBE_LVSUB)) {
              const I32 flags = is_lvalue_sub();
              if (flags && !(flags & OPpENTERSUB_INARGS)) {
                if (gimme != G_LIST)
                    goto croak_cant_return;
                rpp_replace_1_1_NN(sv);
                return NORMAL;
              }
    }

    if (is_pp_rv2av) {
        AV *const av = MUTABLE_AV(sv);

        if (gimme == G_LIST) {
#ifdef PERL_RC_STACK
            SSize_t sp_base = PL_stack_sp - PL_stack_base;
            (void)S_pushav(aTHX_ av);
            /* Now safe to free the original arg on the stack and shuffle
             * down one place anything pushed on top of it */
            SSize_t nitems = PL_stack_sp - (PL_stack_base + sp_base);
            SV *old_sv = PL_stack_sp[-nitems];
            if (nitems)
                Move(PL_stack_sp - nitems + 1,
                     PL_stack_sp - nitems,    nitems, SV*);
            PL_stack_sp--;
            SvREFCNT_dec_NN(old_sv);
            return NORMAL;
#else
            rpp_popfree_1_NN();
            return S_pushav(aTHX_ av);
#endif
        }

        if (gimme == G_SCALAR) {
            const SSize_t maxarg = AvFILL(av) + 1;
            if (PL_op->op_private & OPpTRUEBOOL)
                rpp_replace_1_IMM_NN(maxarg ? &PL_sv_yes : &PL_sv_zero);
            else {
                dTARGET;
                TARGi(maxarg, 1);
                rpp_replace_1_1_NN(targ);
            }
        }
    }
    else {
        /* this static function is responsible for popping sv off stack */
        return S_padhv_rv2hv_common(aTHX_ (HV*)sv, gimme,
                        cBOOL(PL_op->op_private & OPpRV2HV_ISKEYS),
                        1 /* has_targ*/);
    }
    return NORMAL;

 croak_cant_return:
    croak("Can't return %s to lvalue scalar context",
               is_pp_rv2av ? "array" : "hash");
}


STATIC void
S_do_oddball(pTHX_ SV **oddkey, SV **firstkey)
{
    PERL_ARGS_ASSERT_DO_ODDBALL;

    if (*oddkey) {
        if (ckWARN(WARN_MISC)) {
            const char *err;
            if (oddkey == firstkey &&
                SvROK(*oddkey) &&
                (SvTYPE(SvRV(*oddkey)) == SVt_PVAV ||
                 SvTYPE(SvRV(*oddkey)) == SVt_PVHV))
            {
                err = "Reference found where even-sized list expected";
            }
            else
                err = "Odd number of elements in hash assignment";
            warner(packWARN(WARN_MISC), "%s", err);
        }

    }
}


/* Do a mark and sweep with the SVf_BREAK flag to detect elements which
 * are common to both the LHS and RHS of an aassign, and replace them
 * with copies. All these copies are made before the actual list assign is
 * done.
 *
 * For example in ($a,$b) = ($b,$a), assigning the value of the first RHS
 * element ($b) to the first LH element ($a), modifies $a; when the
 * second assignment is done, the second RH element now has the wrong
 * value. So we initially replace the RHS with ($b, copy($a)).
 * Note that we don't need to make a copy of $b.
 *
 * The algorithm below works by, for every RHS element, mark the
 * corresponding LHS target element with SVf_BREAK. Then if the RHS
 * element is found with SVf_BREAK set, it means it would have been
 * modified, so make a copy.
 * Note that by scanning both LHS and RHS in lockstep, we avoid
 * unnecessary copies (like $b above) compared with a naive
 * "mark all LHS; copy all marked RHS; unmark all LHS".
 *
 * If the LHS element is a 'my' declaration' and has a refcount of 1, then
 * it can't be common and can be skipped.
 *
 * On DEBUGGING builds it takes an extra boolean, fake. If true, it means
 * that we thought we didn't need to call S_aassign_copy_common(), but we
 * have anyway for sanity checking. If we find we need to copy, then panic.
 */

PERL_STATIC_INLINE void
S_aassign_copy_common(pTHX_ SV **firstlelem, SV **lastlelem,
        SV **firstrelem, SV **lastrelem
#ifdef DEBUGGING
        , bool fake
#endif
)
{
    SV **relem;
    SV **lelem;
    SSize_t lcount = lastlelem - firstlelem + 1;
    bool marked = FALSE; /* have we marked any LHS with SVf_BREAK ? */
    bool const do_rc1 = cBOOL(PL_op->op_private & OPpASSIGN_COMMON_RC1);
    bool copy_all = FALSE;

    assert(!PL_in_clean_all); /* SVf_BREAK not already in use */
    assert(firstlelem < lastlelem); /* at least 2 LH elements */
    assert(firstrelem < lastrelem); /* at least 2 RH elements */


    lelem = firstlelem;
    /* we never have to copy the first RH element; it can't be corrupted
     * by assigning something to the corresponding first LH element.
     * So this scan does in a loop: mark LHS[N]; test RHS[N+1]
     */
    relem = firstrelem + 1;

    for (; relem <= lastrelem; relem++) {
        SV *svr;

        /* mark next LH element */

        if (--lcount >= 0) {
            SV *svl = *lelem++;

            if (UNLIKELY(!svl)) {/* skip AV alias marker */
                assert (lelem <= lastlelem);
                svl = *lelem++;
                lcount--;
            }

            assert(svl);
            if (SvSMAGICAL(svl)) {
                copy_all = TRUE;
            }
            if (SvTYPE(svl) == SVt_PVAV || SvTYPE(svl) == SVt_PVHV) {
                if (!marked)
                    return;
                /* this LH element will consume all further args;
                 * no need to mark any further LH elements (if any).
                 * But we still need to scan any remaining RHS elements;
                 * set lcount negative to distinguish from  lcount == 0,
                 * so the loop condition continues being true
                 */
                lcount = -1;
                lelem--; /* no need to unmark this element */
            }
            else if (!(do_rc1 &&
#ifdef PERL_RC_STACK
                            SvREFCNT(svl) <= 2
#else
                            SvREFCNT(svl) == 1
#endif
                      ) && !SvIMMORTAL(svl))
            {
                SvFLAGS(svl) |= SVf_BREAK;
                marked = TRUE;
            }
            else if (!marked) {
                /* don't check RH element if no SVf_BREAK flags set yet */
                if (!lcount)
                    break;
                continue;
            }
        }

        /* see if corresponding RH element needs copying */

        assert(marked);
        svr = *relem;
        assert(svr);

        if (UNLIKELY(SvFLAGS(svr) & (SVf_BREAK|SVs_GMG) || copy_all)) {
            U32 brk = (SvFLAGS(svr) & SVf_BREAK);

#ifdef DEBUGGING
            if (fake) {
                /* op_dump(PL_op); */
                croak(
                    "panic: aassign skipped needed copy of common RH elem %"
                        UVuf, (UV)(relem - firstrelem));
            }
#endif

            TAINT_NOT;	/* Each item is independent */

#ifndef PERL_RC_STACK
            /* The TODO test was eventually commented out. It's now been
             * revived, but only on PERL_RC_STACK builds. Continue
             * this hacky workaround otherwise - DAPM Sept 2023 */

            /* Dear TODO test in t/op/sort.t, I love you.
               (It's relying on a panic, not a "semi-panic" from newSVsv()
               and then an assertion failure below.)  */
            if (UNLIKELY(SvIS_FREED(svr))) {
                croak("panic: attempt to copy freed scalar %p",
                           (void*)svr);
            }
#endif

            /* avoid break flag while copying; otherwise COW etc
             * disabled... */
            SvFLAGS(svr) &= ~SVf_BREAK;
            /* Not newSVsv(), as it does not allow copy-on-write,
               resulting in wasteful copies.
               Also, we use SV_NOSTEAL in case the SV is used more than
               once, e.g.  (...) = (f())[0,0]
               Where the same SV appears twice on the RHS without a ref
               count bump.  (Although I suspect that the SV won't be
               stealable here anyway - DAPM).
               */
#ifdef PERL_RC_STACK
            *relem = newSVsv_flags(svr,
                        SV_GMAGIC|SV_DO_COW_SVSETSV|SV_NOSTEAL);
            SvREFCNT_dec_NN(svr);
#else
            *relem = sv_mortalcopy_flags(svr,
                                SV_GMAGIC|SV_DO_COW_SVSETSV|SV_NOSTEAL);
#endif
            /* ... but restore afterwards in case it's needed again,
             * e.g. ($a,$b,$c) = (1,$a,$a)
             */
            SvFLAGS(svr) |= brk;
        }

        if (!lcount)
            break;
    }

    if (!marked)
        return;

    /*unmark LHS */

    while (lelem > firstlelem) {
        SV * const svl = *(--lelem);
        if (svl)
            SvFLAGS(svl) &= ~SVf_BREAK;
    }
}


/* Helper function for pp_aassign(): after performing something like
 *
 *   ($<,$>) = ($>,$<);  # swap real and effective uids
 *
 * the assignment to the magic variables just sets various flags in
 * PL_delaymagic; now we tell the OS to update the uids/gids atomically.
 */

STATIC void
S_aassign_uid(pTHX)
{
    /* Will be used to set PL_tainting below */
    Uid_t tmp_uid  = PerlProc_getuid();
    Uid_t tmp_euid = PerlProc_geteuid();
    Gid_t tmp_gid  = PerlProc_getgid();
    Gid_t tmp_egid = PerlProc_getegid();

    /* XXX $> et al currently silently ignore failures */
    if (PL_delaymagic & DM_UID) {
#ifdef HAS_SETRESUID
        PERL_UNUSED_RESULT(
           setresuid((PL_delaymagic & DM_RUID) ? PL_delaymagic_uid  : (Uid_t)-1,
                     (PL_delaymagic & DM_EUID) ? PL_delaymagic_euid : (Uid_t)-1,
                     (Uid_t)-1));
#elif defined(HAS_SETREUID)
        PERL_UNUSED_RESULT(
            setreuid((PL_delaymagic & DM_RUID) ? PL_delaymagic_uid  : (Uid_t)-1,
                     (PL_delaymagic & DM_EUID) ? PL_delaymagic_euid : (Uid_t)-1));
#else
#  ifdef HAS_SETRUID
        if ((PL_delaymagic & DM_UID) == DM_RUID) {
            PERL_UNUSED_RESULT(setruid(PL_delaymagic_uid));
            PL_delaymagic &= ~DM_RUID;
        }
#  endif /* HAS_SETRUID */
#  ifdef HAS_SETEUID
        if ((PL_delaymagic & DM_UID) == DM_EUID) {
            PERL_UNUSED_RESULT(seteuid(PL_delaymagic_euid));
            PL_delaymagic &= ~DM_EUID;
        }
#  endif /* HAS_SETEUID */
        if (PL_delaymagic & DM_UID) {
            if (PL_delaymagic_uid != PL_delaymagic_euid)
                die("No setreuid available");
            PERL_UNUSED_RESULT(PerlProc_setuid(PL_delaymagic_uid));
        }
#endif /* HAS_SETRESUID */

        tmp_uid  = PerlProc_getuid();
        tmp_euid = PerlProc_geteuid();
    }

    /* XXX $> et al currently silently ignore failures */
    if (PL_delaymagic & DM_GID) {
#ifdef HAS_SETRESGID
        PERL_UNUSED_RESULT(
            setresgid((PL_delaymagic & DM_RGID) ? PL_delaymagic_gid  : (Gid_t)-1,
                      (PL_delaymagic & DM_EGID) ? PL_delaymagic_egid : (Gid_t)-1,
                      (Gid_t)-1));
#elif defined(HAS_SETREGID)
        PERL_UNUSED_RESULT(
            setregid((PL_delaymagic & DM_RGID) ? PL_delaymagic_gid  : (Gid_t)-1,
                     (PL_delaymagic & DM_EGID) ? PL_delaymagic_egid : (Gid_t)-1));
#else
#  ifdef HAS_SETRGID
        if ((PL_delaymagic & DM_GID) == DM_RGID) {
            PERL_UNUSED_RESULT(setrgid(PL_delaymagic_gid));
            PL_delaymagic &= ~DM_RGID;
        }
#  endif /* HAS_SETRGID */
#  ifdef HAS_SETEGID
        if ((PL_delaymagic & DM_GID) == DM_EGID) {
            PERL_UNUSED_RESULT(setegid(PL_delaymagic_egid));
            PL_delaymagic &= ~DM_EGID;
        }
#  endif /* HAS_SETEGID */
        if (PL_delaymagic & DM_GID) {
            if (PL_delaymagic_gid != PL_delaymagic_egid)
                die("No setregid available");
            PERL_UNUSED_RESULT(PerlProc_setgid(PL_delaymagic_gid));
        }
#endif /* HAS_SETRESGID */

        tmp_gid  = PerlProc_getgid();
        tmp_egid = PerlProc_getegid();
    }
    TAINTING_set( TAINTING_get | (tmp_uid && (tmp_euid != tmp_uid || tmp_egid != tmp_gid)) );
#ifdef NO_TAINT_SUPPORT
    PERL_UNUSED_VAR(tmp_uid);
    PERL_UNUSED_VAR(tmp_euid);
    PERL_UNUSED_VAR(tmp_gid);
    PERL_UNUSED_VAR(tmp_egid);
#endif
}


PP(pp_aassign)
{
    SV **lastlelem = PL_stack_sp;
    SV **lastrelem = PL_stack_base + POPMARK;
    SV **firstrelem = PL_stack_base + POPMARK + 1;
    SV **firstlelem = lastrelem + 1;

    SV **relem;
    SV **lelem;
    U8 gimme;
    /* PL_delaymagic is restored by JMPENV_POP on dieing, so we
     * only need to save locally, not on the save stack */
    U16 old_delaymagic = PL_delaymagic;
#ifdef DEBUGGING
    bool fake = 0;
#endif

    PL_delaymagic = DM_DELAY;		/* catch simultaneous items */

    /* If there's a common identifier on both sides we have to take
     * special care that assigning the identifier on the left doesn't
     * clobber a value on the right that's used later in the list.
     */

    /* at least 2 LH and RH elements, or commonality isn't an issue */
    if (firstlelem < lastlelem && firstrelem < lastrelem) {
        for (relem = firstrelem+1; relem <= lastrelem; relem++) {
            if (SvGMAGICAL(*relem))
                goto do_scan;
        }
        for (lelem = firstlelem; lelem <= lastlelem; lelem++) {
            if (*lelem && SvSMAGICAL(*lelem))
                goto do_scan;
        }
        if ( PL_op->op_private & (OPpASSIGN_COMMON_SCALAR|OPpASSIGN_COMMON_RC1) ) {
            if (PL_op->op_private & OPpASSIGN_COMMON_RC1) {
                /* skip the scan if all scalars have a ref count of 1 */
                for (lelem = firstlelem; lelem <= lastlelem; lelem++) {
                    SV *sv = *lelem;
                    if (!sv ||
#ifdef PERL_RC_STACK
                        SvREFCNT(sv) <= 2
#else
                        SvREFCNT(sv) == 1
#endif
                    )
                        continue;
                    if (SvTYPE(sv) != SVt_PVAV && SvTYPE(sv) != SVt_PVAV)
                        goto do_scan;
                    break;
                }
            }
            else {
            do_scan:
                S_aassign_copy_common(aTHX_
                                      firstlelem, lastlelem, firstrelem, lastrelem
#ifdef DEBUGGING
                    , fake
#endif
                );
            }
        }
    }
#ifdef DEBUGGING
    else {
        /* on debugging builds, do the scan even if we've concluded we
         * don't need to, then panic if we find commonality. Note that the
         * scanner assumes at least 2 elements */
        if (firstlelem < lastlelem && firstrelem < lastrelem) {
            fake = 1;
            goto do_scan;
        }
    }
#endif

    gimme = GIMME_V;
    bool is_list = (gimme == G_LIST);
    relem = firstrelem;
    lelem = firstlelem;
#ifdef PERL_RC_STACK
    /* Where we can reset stack to at the end, without needing to free
     * each element. This is normally all the lelem's, but it can vary for
     * things like odd number of hash elements, which pushes a
     * &PL_sv_undef into the 'lvalue' part of the stack.
     */
    SV ** first_discard = firstlelem;
#endif

    if (relem > lastrelem)
        goto no_relems;

    /* first lelem loop while there are still relems */
    while (LIKELY(lelem <= lastlelem)) {
        bool alias = FALSE;
        SV *lsv = *lelem;

        TAINT_NOT; /* Each item stands on its own, taintwise. */

        assert(relem <= lastrelem);
        if (UNLIKELY(!lsv)) {
            alias = TRUE;
            lsv = *++lelem;
            ASSUME(SvTYPE(lsv) == SVt_PVAV);
        }

        switch (SvTYPE(lsv)) {
        case SVt_PVAV: {
            SV **svp;
            SSize_t i;
            SSize_t nelems = lastrelem - relem + 1;
            AV *ary = MUTABLE_AV(lsv);

            /* Assigning to an aggregate is tricky. First there is the
             * issue of commonality, e.g. @a = ($a[0]). Since the
             * stack isn't refcounted, clearing @a prior to storing
             * elements will free $a[0]. Similarly with
             *    sub FETCH { $status[$_[1]] } @status = @tied[0,1];
             *
             * The way to avoid these issues is to make the copy of each
             * SV (and we normally store a *copy* in the array) *before*
             * clearing the array. But this has a problem in that
             * if the code croaks during copying, the not-yet-stored copies
             * could leak. One way to avoid this is to make all the copies
             * mortal, but that's quite expensive.
             *
             * The current solution to these issues is to use a chunk
             * of the tmps stack as a temporary refcounted-stack. SVs
             * will be put on there during processing to avoid leaks,
             * but will be removed again before the end of this block,
             * so free_tmps() is never normally called. Also, the
             * sv_refcnt of the SVs doesn't have to be manipulated, since
             * the ownership of 1 reference count is transferred directly
             * from the tmps stack to the AV when the SV is stored.
             *
             * We disarm slots in the temps stack by storing PL_sv_undef
             * there: it doesn't matter if that SV's refcount is
             * repeatedly decremented during a croak. But usually this is
             * only an interim measure. By the end of this code block
             * we try where possible to not leave any PL_sv_undef's on the
             * tmps stack e.g. by shuffling newer entries down.
             *
             * There is one case where we don't copy: non-magical
             * SvTEMP(sv)'s with a ref count of 1. The only owner of these
             * is on the tmps stack, so its safe to directly steal the SV
             * rather than copying. This is common in things like function
             * returns, map etc, which all return a list of such SVs.
             *
             * Note however something like @a = (f())[0,0], where there is
             * a danger of the same SV being shared:  this avoided because
             * when the SV is stored as $a[0], its ref count gets bumped,
             * so the RC==1 test fails and the second element is copied
             * instead.
             *
             * We also use one slot in the tmps stack to hold an extra
             * ref to the array, to ensure it doesn't get prematurely
             * freed. Again, this is removed before the end of this block.
             *
             * Note that OPpASSIGN_COMMON_AGG is used to flag a possible
             * @a = ($a[0]) case, but the current implementation uses the
             * same algorithm regardless, so ignores that flag. (It *is*
             * used in the hash branch below, however).
             *
             *
             * The net effect of this next block of code (apart from
             * optimisations and aliasing) is to make a copy of each
             * *relem and store the new SV both in the array and back on
             * the *relem slot of the stack, overwriting the original.
             * This new list of SVs will later be either returned
             * (G_LIST), or popped.
             *
             * Note that under PERL_RC_STACK builds most of this
             * complexity can be thrown away: things can be kept alive on
             * the argument stack without involving the temps stack. In
             * particular, the args are kept on the argument stack and
             * processed from there, rather than their pointers being
             * copied to the temps stack and then processed from there.
             */

#ifndef PERL_RC_STACK
            /* Reserve slots for ary, plus the elems we're about to copy,
             * then protect ary and temporarily void the remaining slots
             * with &PL_sv_undef */
            EXTEND_MORTAL(nelems + 1);
            PL_tmps_stack[++PL_tmps_ix] = SvREFCNT_inc_simple_NN(ary);
            SSize_t tmps_base = PL_tmps_ix + 1;
            for (i = 0; i < nelems; i++)
                PL_tmps_stack[tmps_base + i] = &PL_sv_undef;
            PL_tmps_ix += nelems;
#endif

            /* Make a copy of each RHS elem and save on the tmps_stack
             * (or pass through where we can optimise away the copy) */

            if (UNLIKELY(alias)) {
                U32 lval = (is_list)
                                ? (PL_op->op_flags & OPf_MOD || LVRET) : 0;
                for (svp = relem; svp <= lastrelem; svp++) {
                    SV *rsv = *svp;

                    SvGETMAGIC(rsv);
                    if (!SvROK(rsv))
                        DIE(aTHX_ "Assigned value is not a reference");
                    if (SvTYPE(SvRV(rsv)) > SVt_PVLV)
                   /* diag_listed_as: Assigned value is not %s reference */
                        DIE(aTHX_
                           "Assigned value is not a SCALAR reference");
                    if (lval) {
                        /* XXX the 'mortal' part here is probably
                         * unnecessary under PERL_RC_STACK.
                         */
                        rsv = sv_mortalcopy(rsv);
                        rpp_replace_at_NN(svp, rsv);
                    }
                    /* XXX else check for weak refs?  */
#ifndef PERL_RC_STACK
                    rsv = SvREFCNT_inc_NN(SvRV(rsv));
                    assert(tmps_base <= PL_tmps_max);
                    PL_tmps_stack[tmps_base++] = rsv;
#endif
                }
            }
            else {
                for (svp = relem; svp <= lastrelem; svp++) {
                    SV *rsv = *svp;

                    if (rpp_is_lone(rsv) && !SvGMAGICAL(rsv)) {
                        /* can skip the copy */
#ifndef PERL_RC_STACK
                        SvREFCNT_inc_simple_void_NN(rsv);
#endif
                        SvTEMP_off(rsv);
                    }
                    else {
                        SV *nsv;
                        /* see comment in S_aassign_copy_common about
                         * SV_NOSTEAL */
                        nsv = newSVsv_flags(rsv,
                                (SV_DO_COW_SVSETSV|SV_NOSTEAL|SV_GMAGIC));
#ifdef PERL_RC_STACK
                        rpp_replace_at_norc_NN(svp, nsv);
#else
                        /* using rpp_replace_at_norc() would mortalise,
                         * but we're manually adding nsv to the tmps stack
                         * below already */
                        rpp_replace_at_NN(svp, nsv);
#endif

                        rsv = nsv;
                    }

#ifndef PERL_RC_STACK
                    assert(tmps_base <= PL_tmps_max);
                    PL_tmps_stack[tmps_base++] = rsv;
#endif
                }
            }

            if (SvRMAGICAL(ary) || AvFILLp(ary) >= 0) /* may be non-empty */
                av_clear(ary);

            /* Store in the array, the argument copies that are in the
             * tmps stack (or for PERL_RC_STACK, on the args stack) */

#ifndef PERL_RC_STACK
            tmps_base -= nelems;
#endif
            if (alias || SvMAGICAL(ary) || SvREADONLY(ary) || !AvREAL(ary)) {
                /* for arrays we can't cheat with, use the official API */
                av_extend(ary, nelems - 1);
                for (i = 0; i < nelems; i++) {
                    SV **svp =
#ifdef PERL_RC_STACK
                        &relem[i];
#else
                        &(PL_tmps_stack[tmps_base + i]);
#endif

                    SV *rsv = *svp;
#ifdef PERL_RC_STACK
                    if (alias) {
                        assert(SvROK(rsv));
                        rsv = SvRV(rsv);
                    }
#endif

                    /* A tied store won't take ownership of rsv, so keep
                     * the 1 refcnt on the tmps stack; otherwise disarm
                     * the tmps stack entry */
                    if (av_store(ary, i, rsv))
#ifdef PERL_RC_STACK
                        SvREFCNT_inc_simple_NN(rsv);
#else
                        *svp = &PL_sv_undef;
#endif
                    /* av_store() may have added set magic to rsv */;
                    SvSETMAGIC(rsv);
                }
#ifndef PERL_RC_STACK
                /* disarm ary refcount: see comments below about leak */
                PL_tmps_stack[tmps_base - 1] = &PL_sv_undef;
#endif
            }
            else {
                /* Simple array: directly access/set the guts of the AV */
                SSize_t fill = nelems - 1;
                if (fill > AvMAX(ary))
                    av_extend_guts(ary, fill, &AvMAX(ary), &AvALLOC(ary),
                                    &AvARRAY(ary));
                AvFILLp(ary) = fill;
#ifdef PERL_RC_STACK
                Copy(relem, AvARRAY(ary), nelems, SV*);
                /* ownership of one ref count of each elem passed to
                 * array. Quietly remove old SVs from stack, or if need
                 * to keep the list on the stack too, bump the count */
                if (UNLIKELY(is_list))
                    for (i = 0; i < nelems; i++)
                        SvREFCNT_inc_void_NN(relem[i]);
                else {
                    assert(first_discard == relem + nelems);
                    Zero(relem, nelems, SV*);
                    first_discard = relem;
                }
#else
                Copy(&(PL_tmps_stack[tmps_base]), AvARRAY(ary), nelems, SV*);
                /* Quietly remove all the SVs from the tmps stack slots,
                 * since ary has now taken ownership of the refcnt.
                 * Also remove ary: which will now leak if we die before
                 * the SvREFCNT_dec_NN(ary) below */
                if (UNLIKELY(PL_tmps_ix >= tmps_base + nelems))
                    Move(&PL_tmps_stack[tmps_base + nelems],
                         &PL_tmps_stack[tmps_base - 1],
                         PL_tmps_ix - (tmps_base + nelems) + 1,
                         SV*);
                PL_tmps_ix -= (nelems + 1);
#endif
            }

            if (UNLIKELY(PL_delaymagic & DM_ARRAY_ISA))
                /* its assumed @ISA set magic can't die and leak ary */
                SvSETMAGIC(MUTABLE_SV(ary));

#ifdef PERL_RC_STACK
            assert(*lelem == (SV*)ary);
            *lelem = NULL;
#endif
            lelem++;
            SvREFCNT_dec_NN(ary);
            relem = lastrelem + 1;
            goto no_relems;
        }

        case SVt_PVHV: {				/* normal hash */

            SV **svp;
            SSize_t i;
            SSize_t nelems = lastrelem - relem + 1;
            HV *hash = MUTABLE_HV(lsv);

            if (UNLIKELY(nelems & 1)) {
                do_oddball(lastrelem, relem);
                /* we have firstlelem to reuse, it's not needed any more */
#ifdef PERL_RC_STACK
                if (lelem == lastrelem + 1) {
                    /* the lelem slot we want to use is the 
                     * one keeping hash alive. Mortalise the hash
                     * so it doesn't leak */
                    assert(lastrelem[1] == (SV*)hash);
                    sv_2mortal((SV*)hash);
                }
                else {
                    /* safe to repurpose old lelem slot */
                    assert(!lastrelem[1] || SvIMMORTAL(lastrelem[1]));
                }
                first_discard++;
                assert(first_discard = lastrelem + 2);
#endif
                *++lastrelem = &PL_sv_undef;
                nelems++;
            }

            /* See the SVt_PVAV branch above for a long description of
             * how the following all works. The main difference for hashes
             * is that we treat keys and values separately (and have
             * separate loops for them): as for arrays, values are always
             * copied (except for the SvTEMP optimisation), since they
             * need to be stored in the hash; while keys are only
             * processed where they might get prematurely freed or
             * whatever. The same comments about simplifying under
             * PERL_RC_STACK apply here too */

            /* tmps stack slots:
             * * reserve a slot for the hash keepalive;
             * * reserve slots for the hash values we're about to copy;
             * * preallocate for the keys we'll possibly copy or refcount bump
             *   later;
             * then protect hash and temporarily void the remaining
             * value slots with &PL_sv_undef */
#ifndef PERL_RC_STACK
            EXTEND_MORTAL(nelems + 1);
#endif
             /* convert to number of key/value pairs */
             nelems >>= 1;

#ifndef PERL_RC_STACK
            PL_tmps_stack[++PL_tmps_ix] = SvREFCNT_inc_simple_NN(hash);
            SSize_t tmps_base = PL_tmps_ix + 1;
            for (i = 0; i < nelems; i++)
                PL_tmps_stack[tmps_base + i] = &PL_sv_undef;
            PL_tmps_ix += nelems;
#endif

            /* Make a copy of each RHS hash value and save on the tmps_stack
             * (or pass through where we can optimise away the copy) */

            for (svp = relem + 1; svp <= lastrelem; svp += 2) {
                SV *rsv = *svp;

                if (rpp_is_lone(rsv) && !SvGMAGICAL(rsv)) {
                    /* can skip the copy */
#ifndef PERL_RC_STACK
                    SvREFCNT_inc_simple_void_NN(rsv);
#endif
                    SvTEMP_off(rsv);
                }
                else {
                    SV *nsv;
                    /* see comment in S_aassign_copy_common about
                     * SV_NOSTEAL */
                    nsv = newSVsv_flags(rsv,
                            (SV_DO_COW_SVSETSV|SV_NOSTEAL|SV_GMAGIC));
#ifdef PERL_RC_STACK
                    rpp_replace_at_norc_NN(svp, nsv);
#else
                    /* using rpp_replace_at_norc() would mortalise,
                     * but we're manually adding nsv to the tmps stack
                     * below already */
                    rpp_replace_at_NN(svp, nsv);
#endif
                    rsv = nsv;
                }

#ifndef PERL_RC_STACK
                assert(tmps_base <= PL_tmps_max);
                PL_tmps_stack[tmps_base++] = rsv;
#endif
            }

#ifndef PERL_RC_STACK
            tmps_base -= nelems;
#endif


            /* possibly protect keys */

            if (UNLIKELY(is_list)) {
                /* handle e.g.
                *     @a = ((%h = ($$r, 1)), $r = "x");
                *     $_++ for %h = (1,2,3,4);
                */
#ifndef PERL_RC_STACK
                EXTEND_MORTAL(nelems);
#endif
                for (svp = relem; svp <= lastrelem; svp += 2) {
                    rpp_replace_at_norc_NN(svp,
                        newSVsv_flags(*svp,
                                SV_GMAGIC|SV_DO_COW_SVSETSV|SV_NOSTEAL));
                }
            }
            else if (PL_op->op_private & OPpASSIGN_COMMON_AGG) {
                /* for possible commonality, e.g.
                 *       %h = ($h{a},1)
                 * avoid premature freeing RHS keys by mortalising
                 * them.
                 * For a magic element, make a copy so that its magic is
                 * called *before* the hash is emptied (which may affect
                 * a tied value for example).
                 * In theory we should check for magic keys in all
                 * cases, not just under OPpASSIGN_COMMON_AGG, but in
                 * practice, !OPpASSIGN_COMMON_AGG implies only
                 * constants or padtmps on the RHS.
                 *
                 * For PERL_RC_STACK, no danger of premature frees, so
                 * just handle the magic.
                 */
#ifdef PERL_RC_STACK
                for (svp = relem; svp <= lastrelem; svp += 2) {
                    SV *rsv = *svp;
                    if (UNLIKELY(SvGMAGICAL(rsv)))
                        /* XXX does this actually need to be copied, or
                         * could we just call the get magic??? */
                        rpp_replace_at_norc_NN(svp,
                            newSVsv_flags(rsv,
                                SV_GMAGIC|SV_DO_COW_SVSETSV|SV_NOSTEAL));
                }
#else
                EXTEND_MORTAL(nelems);
                for (svp = relem; svp <= lastrelem; svp += 2) {
                    SV *rsv = *svp;
                    if (UNLIKELY(SvGMAGICAL(rsv))) {
                        SSize_t n;
                        rpp_replace_at_norc_NN(svp,
                            newSVsv_flags(rsv,
                                SV_GMAGIC|SV_DO_COW_SVSETSV|SV_NOSTEAL));
                        /* allow other branch to continue pushing
                         * onto tmps stack without checking each time */
                        n = (lastrelem - relem) >> 1;
                        EXTEND_MORTAL(n);
                    }
                    else
                        PL_tmps_stack[++PL_tmps_ix] =
                                    SvREFCNT_inc_simple_NN(rsv);
                }
#endif
            }

            if (SvRMAGICAL(hash) || HvUSEDKEYS(hash))
                hv_clear(hash);

            /* "nelems" was converted to the number of pairs earlier. */
            if (nelems > PERL_HASH_DEFAULT_HvMAX) {
                hv_ksplit(hash, nelems);
            }

            /* now assign the keys and values to the hash */

#ifndef PERL_RC_STACK
            bool dirty_tmps = FALSE;
#endif
            if (UNLIKELY(is_list)) {
                /* @a = (%h = (...)) etc */
                SV **svp;
                SV **topelem = relem;

                for (i = 0, svp = relem; svp <= lastrelem; i++, svp++) {
                    SV *key = *svp++;
                    SV *val = *svp;
                    /* remove duplicates from list we return */
                    if (!hv_exists_ent(hash, key, 0)) {
                        /* copy key back: possibly to an earlier
                         * stack location if we encountered dups earlier,
                         * The values will be updated later
                         */
                        rpp_replace_at_NN(topelem, key);
                        topelem += 2;
                    }
                    /* A tied store won't take ownership of val, so keep
                     * the 1 refcnt on the tmps stack; otherwise disarm
                     * the tmps stack entry */
                    if (hv_store_ent(hash, key, val, 0))
#ifdef PERL_RC_STACK
                        SvREFCNT_inc_simple_NN(val);
#else
                        PL_tmps_stack[tmps_base + i] = &PL_sv_undef;
                    else
                        dirty_tmps = TRUE;
#endif
                    /* hv_store_ent() may have added set magic to val */;
                    SvSETMAGIC(val);
                }

                if (topelem < svp) {
                    /* at this point we have removed the duplicate key/value
                     * pairs from the stack, but the remaining values may be
                     * wrong; i.e. with (a 1 a 2 b 3) on the stack we've removed
                     * the (a 2), but the stack now probably contains
                     * (a <freed> b 3), because { hv_save(a,1); hv_save(a,2) }
                     * obliterates the earlier key. So refresh all values. */
                    lastrelem = topelem - 1;
                    while (relem < lastrelem) {
                        HE *he;
                        he = hv_fetch_ent(hash, *relem++, 0, 0);
                        rpp_replace_at_NN(relem++,
                            (he ? HeVAL(he) : &PL_sv_undef));
                    }
                }
            }
            else {
                SV **svp;
                for (i = 0, svp = relem; svp <= lastrelem; i++, svp++) {
                    SV *key = *svp++;
                    SV *val = *svp;
#ifdef PERL_RC_STACK
                    {
                        HE *stored = hv_store_ent(hash, key, val, 0);
                        /* hv_store_ent() may have added set magic to val */;
                        SvSETMAGIC(val);
                        /* remove key and val from stack */
                        *svp = NULL;
                        if (!stored)
                            SvREFCNT_dec_NN(val);
                        svp[-1] = NULL;
                        SvREFCNT_dec_NN(key);
                    }
#else
                    if (hv_store_ent(hash, key, val, 0))
                        PL_tmps_stack[tmps_base + i] = &PL_sv_undef;
                    else
                        dirty_tmps = TRUE;
                    /* hv_store_ent() may have added set magic to val */;
                    SvSETMAGIC(val);
#endif
                }
#ifdef PERL_RC_STACK
                /* now that all the key and val slots on the stack have
                 * been discarded, we can skip freeing them on return */
                assert(first_discard == lastrelem + 1);
                first_discard = relem;
#endif
            }

#ifdef PERL_RC_STACK
            /* Disarm the ref-counted pointer on the stack. This will
             * usually point to the hash, except for the case of an odd
             * number of elems where the hash was mortalised and its slot
             * on the stack was made part of the relems with the slot's
             * value overwritten with &PL_sv_undef. */
            if (*lelem == (SV*)hash) {
                *lelem = NULL;
                SvREFCNT_dec_NN(hash);
            }
#else
            if (dirty_tmps) {
                /* there are still some 'live' recounts on the tmps stack
                 * - usually caused by storing into a tied hash. So let
                 * free_tmps() do the proper but slow job later.
                 * Just disarm hash refcount: see comments below about leak
                 */
                PL_tmps_stack[tmps_base - 1] = &PL_sv_undef;
            }
            else {
                /* Quietly remove all the SVs from the tmps stack slots,
                 * since hash has now taken ownership of the refcnt.
                 * Also remove hash: which will now leak if we die before
                 * the SvREFCNT_dec_NN(hash) below */
                if (UNLIKELY(PL_tmps_ix >= tmps_base + nelems))
                    Move(&PL_tmps_stack[tmps_base + nelems],
                         &PL_tmps_stack[tmps_base - 1],
                         PL_tmps_ix - (tmps_base + nelems) + 1,
                         SV*);
                PL_tmps_ix -= (nelems + 1);
            }

            SvREFCNT_dec_NN(hash);
#endif
            lelem++;
            relem = lastrelem + 1;
            goto no_relems;
        }

        default:
            if (!SvIMMORTAL(lsv)) {
                if (UNLIKELY(
                    rpp_is_lone(lsv) && !SvSMAGICAL(lsv) &&
                  (!isGV_with_GP(lsv) || SvFAKE(lsv)) && ckWARN(WARN_MISC)
                ))
                    warner(packWARN(WARN_MISC),
                           "Useless assignment to a temporary");

#ifndef PERL_RC_STACK
                /* avoid freeing $$lsv if it might be needed for further
                 * elements, e.g. ($ref, $foo) = (1, $$ref) */
                SV *ref;
                if (   SvROK(lsv)
                    && ( ((ref = SvRV(lsv)), SvREFCNT(ref)) == 1)
                    && lelem < lastlelem
                ) {
                    SSize_t ix;
                    SvREFCNT_inc_simple_void_NN(ref);
                    /* an unrolled sv_2mortal */
                    ix = ++PL_tmps_ix;
                    if (UNLIKELY(ix >= PL_tmps_max))
                        /* speculatively grow enough to cover other
                         * possible refs */
                         (void)tmps_grow_p(ix + (lastlelem - lelem + 1));
                    PL_tmps_stack[ix] = ref;
                }
#endif

                sv_setsv(lsv, *relem);
                SvSETMAGIC(lsv);
                if (UNLIKELY(is_list))
                    rpp_replace_at_NN(relem, lsv);
#ifdef PERL_RC_STACK
                *lelem = NULL;
                SvREFCNT_dec_NN(lsv);
#endif
            }
            lelem++;
            if (++relem > lastrelem)
                goto no_relems;
            break;
        } /* switch */
    } /* while */


  no_relems:

    /* simplified lelem loop for when there are no relems left */
    while (LIKELY(lelem <= lastlelem)) {
        SV *lsv = *lelem;

        TAINT_NOT; /* Each item stands on its own, taintwise. */

        if (UNLIKELY(!lsv)) {
            lsv = *++lelem;
            ASSUME(SvTYPE(lsv) == SVt_PVAV);
        }

        switch (SvTYPE(lsv)) {
        case SVt_PVAV:
            if (SvRMAGICAL(lsv) || AvFILLp((SV*)lsv) >= 0) {
                av_clear((AV*)lsv);
                if (UNLIKELY(PL_delaymagic & DM_ARRAY_ISA))
                    SvSETMAGIC(lsv);
            }
            break;

        case SVt_PVHV:
            if (SvRMAGICAL(lsv) || HvUSEDKEYS((HV*)lsv))
                hv_clear((HV*)lsv);
            break;

        default:
            if (!SvIMMORTAL(lsv)) {
                sv_set_undef(lsv);
                SvSETMAGIC(lsv);
            }
            if (UNLIKELY(is_list)) {
                /* this usually grows the list of relems to be returned
                 * into the stack space holding lelems (unless
                 * there was previously a hash with dup elements) */
#ifdef PERL_RC_STACK
                assert(relem <= first_discard);
                assert(relem <= lelem);
                if (relem == first_discard)
                    first_discard++;
#endif
                rpp_replace_at(relem++, lsv);
#ifdef PERL_RC_STACK
                if (relem == lelem + 1) {
                    lelem++;
                    /* skip the NULLing of the slot */
                    continue;
                }
#endif
            }
            break;
        } /* switch */
#ifdef PERL_RC_STACK
        *lelem = NULL;
        SvREFCNT_dec_NN(lsv);
#endif
        lelem++;
    } /* while */

    TAINT_NOT; /* result of list assign isn't tainted */

    if (UNLIKELY(PL_delaymagic & ~DM_DELAY))
        /* update system UIDs and/or GIDs */
        S_aassign_uid(aTHX);
    PL_delaymagic = old_delaymagic;

#ifdef PERL_RC_STACK
    /* On ref-counted builds, the code above should have stored
     * NULL in each lelem field and already freed each lelem. Thus
     * the popfree_to() can start at a lower point.
     * Under some circumstances, &PL_sv_undef might be stored rather than
     * NULL, but this also doesn't need its refcount decrementing.
     * Assert that this is true.
     * Note that duplicate hash keys in list context can cause
     * lastrelem and relem to be lower than at the start;
     * while an odd number of hash elements can cause lastrelem to
     * have a value one higher than at the start */
#  ifdef DEBUGGING
    for (SV **svp = first_discard; svp <= PL_stack_sp; svp++)
        assert(!*svp || SvIMMORTAL(*svp));
#  endif
    PL_stack_sp = first_discard - 1;

    /* now pop all the R elements too */
    rpp_popfree_to_NN((is_list ? relem : firstrelem) - 1);

#else
    /* pop all L and R elements apart from any being returned */
    rpp_popfree_to_NN((is_list ? relem : firstrelem) - 1);
#endif

    if (gimme == G_SCALAR) {
        rpp_extend(1);
        SV *sv;
        if (PL_op->op_private & OPpASSIGN_TRUEBOOL)
            rpp_push_IMM((firstlelem - firstrelem) ? &PL_sv_yes : &PL_sv_zero);
        else {
            dTARGET;
            TARGi(firstlelem - firstrelem, 1);
            sv = targ;
            rpp_push_1(sv);
        }
    }

    return NORMAL;
}


PP(pp_qr)
{
    PMOP * const pm = cPMOP;
    REGEXP * rx = PM_GETRE(pm);
    regexp *prog = ReANY(rx);
    SV * const pkg = RXp_ENGINE(prog)->qr_package(aTHX_ (rx));
    SV * const rv = newSV_type_mortal(SVt_IV);
    CV **cvp;
    CV *cv;

    SvUPGRADE(rv, SVt_IV);
    /* For a subroutine describing itself as "This is a hacky workaround" I'm
       loathe to use it here, but it seems to be the right fix. Or close.
       The key part appears to be that it's essential for pp_qr to return a new
       object (SV), which implies that there needs to be an effective way to
       generate a new SV from the existing SV that is pre-compiled in the
       optree.  */
    SvRV_set(rv, MUTABLE_SV(reg_temp_copy(NULL, rx)));
    SvROK_on(rv);

    cvp = &( ReANY((REGEXP *)SvRV(rv))->qr_anoncv);
    if (UNLIKELY((cv = *cvp) && CvCLONE(*cvp))) {
        *cvp = cv_clone(cv);
        SvREFCNT_dec_NN(cv);
    }

    if (pkg) {
        HV *const stash = gv_stashsv(pkg, GV_ADD);
        SvREFCNT_dec_NN(pkg);
        (void)sv_bless(rv, stash);
    }

    if (UNLIKELY(RXp_ISTAINTED(prog))) {
        SvTAINTED_on(rv);
        SvTAINTED_on(SvRV(rv));
    }
    rpp_xpush_1(rv);
    return NORMAL;
}

STATIC bool
S_are_we_in_Debug_EXECUTE_r(pTHX)
{
    /* Given a 'use re' is in effect, does it ask for outputting execution
     * debug info?
     *
     * This is separated from the sole place it's called, an inline function,
     * because it is the large-ish slow portion of the function */

    DECLARE_AND_GET_RE_DEBUG_FLAGS_NON_REGEX;

    return cBOOL(RE_DEBUG_FLAG(RE_DEBUG_EXECUTE_MASK));
}

PERL_STATIC_INLINE bool
S_should_we_output_Debug_r(pTHX_ regexp *prog)
{
    PERL_ARGS_ASSERT_SHOULD_WE_OUTPUT_DEBUG_R;

    /* pp_match can output regex debugging info.  This function returns a
     * boolean as to whether or not it should.
     *
     * Under -Dr, it should.  Any reasonable compiler will optimize this bit of
     * code away on non-debugging builds. */
    if (UNLIKELY(DEBUG_r_TEST)) {
        return TRUE;
    }

    /* If the regex engine is using the non-debugging execution routine, then
     * no debugging should be output.  Same if the field is NULL that pluggable
     * engines are not supposed to fill. */
    if (     LIKELY(prog->engine->exec == &Perl_regexec_flags)
        || UNLIKELY(prog->engine->op_comp == NULL))
    {
        return FALSE;
    }

    /* Otherwise have to check */
    return S_are_we_in_Debug_EXECUTE_r(aTHX);
}


PP(pp_match)
{
    SV *targ;
    PMOP *pm = cPMOP;
    PMOP *dynpm = pm;
    const char *s;
    const char *strend;
    SSize_t curpos = 0; /* initial pos() or current $+[0] */
    I32 global;
    U8 r_flags = 0;
    const char *truebase;			/* Start of string  */
    REGEXP *rx = PM_GETRE(pm);
    regexp *prog = ReANY(rx);
    bool rxtainted;
    const U8 gimme = GIMME_V;
    STRLEN len;
    const I32 oldsave = PL_savestack_ix;
    I32 had_zerolen = 0;
    MAGIC *mg = NULL;
    SSize_t sp_base;

    if (PL_op->op_flags & OPf_STACKED) {
        targ = PL_stack_sp[0];
        /* We have to keep targ alive on the stack. At the end we have to
         * free it and shuffle down all the return values by one.
         * Remember the position.
         */
        sp_base = PL_stack_sp - PL_stack_base;
        assert(sp_base > 0);
    }
    else {
        sp_base = 0;
        if (PL_op->op_targ)
            targ = PAD_SV(PL_op->op_targ);
        else {
            targ = DEFSV;
        }
        rpp_extend(1);
    }

    /* Skip get-magic if this is a qr// clone, because regcomp has
       already done it. */
    truebase = prog->mother_re
         ? SvPV_nomg_const(TARG, len)
         : SvPV_const(TARG, len);
    if (!truebase)
        DIE(aTHX_ "panic: pp_match");
    strend = truebase + len;
    rxtainted = (RXp_ISTAINTED(prog) ||
                 (TAINT_get && (pm->op_pmflags & PMf_RETAINT)));
    TAINT_NOT;

    /* We need to know this in case we fail out early - pos() must be reset */
    global = dynpm->op_pmflags & PMf_GLOBAL;

    /* PMdf_USED is set after a ?? matches once */
    if (
#ifdef USE_ITHREADS
        SvREADONLY(PL_regex_pad[pm->op_pmoffset])
#else
        pm->op_pmflags & PMf_USED
#endif
    ) {
        if (UNLIKELY(should_we_output_Debug_r(prog))) {
            PerlIO_printf(Perl_debug_log, "?? already matched once");
        }
        goto nope;
    }

    /* handle the empty pattern */
    if (!RX_PRELEN(rx) && PL_curpm && !prog->mother_re) {
        if (PL_curpm == PL_reg_curpm) {
            if (PL_curpm_under) {
                if (PL_curpm_under == PL_reg_curpm) {
                    croak("Infinite recursion via empty pattern");
                } else {
                    pm = PL_curpm_under;
                }
            }
        } else {
            pm = PL_curpm;
        }
        rx = PM_GETRE(pm);
        prog = ReANY(rx);
    }

    if (RXp_MINLEN(prog) >= 0 && (STRLEN)RXp_MINLEN(prog) > len) {
        if (UNLIKELY(should_we_output_Debug_r(prog))) {
            PerlIO_printf(Perl_debug_log,
                "String shorter than min possible regex match (%zd < %zd)\n",
                                                        len, RXp_MINLEN(prog));
        }
        goto nope;
    }

    /* get pos() if //g */
    if (global) {
        mg = mg_find_mglob(TARG);
        if (mg && mg->mg_len >= 0) {
            curpos = MgBYTEPOS(mg, TARG, truebase, len);
            /* last time pos() was set, it was zero-length match */
            if (mg->mg_flags & MGf_MINMATCH)
                had_zerolen = 1;
        }
    }

#ifdef PERL_SAWAMPERSAND
    if (       RXp_NPARENS(prog)
            || PL_sawampersand
            || (RXp_EXTFLAGS(prog) & (RXf_EVAL_SEEN|RXf_PMf_KEEPCOPY))
            || (dynpm->op_pmflags & PMf_KEEPCOPY)
    )
#endif
    {
        r_flags |= (REXEC_COPY_STR|REXEC_COPY_SKIP_PRE);
        /* In @a = /(.)/g, we iterate multiple times, but copy the buffer
         * only on the first iteration. Therefore we need to copy $' as well
         * as $&, to make the rest of the string available for captures in
         * subsequent iterations */
        if (! (global && gimme == G_LIST))
            r_flags |= REXEC_COPY_SKIP_POST;
    };
#ifdef PERL_SAWAMPERSAND
    if (dynpm->op_pmflags & PMf_KEEPCOPY)
        /* handle KEEPCOPY in pmop but not rx, eg $r=qr/a/; /$r/p */
        r_flags &= ~(REXEC_COPY_SKIP_PRE|REXEC_COPY_SKIP_POST);
#endif

    s = truebase;

  play_it_again:
    if (global)
        s = truebase + curpos;

    if (!CALLREGEXEC(rx, (char*)s, (char *)strend, (char*)truebase,
                     had_zerolen, TARG, NULL, r_flags))
        goto nope;

    PL_curpm = pm;
    if (dynpm->op_pmflags & PMf_ONCE)
#ifdef USE_ITHREADS
        SvREADONLY_on(PL_regex_pad[dynpm->op_pmoffset]);
#else
        dynpm->op_pmflags |= PMf_USED;
#endif

    if (rxtainted)
        RXp_MATCH_TAINTED_on(prog);
    TAINT_IF(RXp_MATCH_TAINTED(prog));

    /* update pos */

    if (global && (gimme != G_LIST || (dynpm->op_pmflags & PMf_CONTINUE))) {
        if (!mg)
            mg = sv_magicext_mglob(TARG);
        MgBYTEPOS_set(mg, TARG, truebase, RXp_OFFS_END(prog,0));
        if (RXp_ZERO_LEN(prog))
            mg->mg_flags |= MGf_MINMATCH;
        else
            mg->mg_flags &= ~MGf_MINMATCH;
    }

    if ((!RXp_NPARENS(prog) && !global) || gimme != G_LIST) {
        LEAVE_SCOPE(oldsave);
        if (sp_base)
            rpp_popfree_1(); /* free arg */
        rpp_push_IMM(&PL_sv_yes);
        return NORMAL;
    }

    /* push captures on stack */

    {
        const I32 logical_nparens = RXp_LOGICAL_NPARENS(prog);
        /* This following statement is *devious* code. If we are in a global
           match and the pattern has no parens in it, we should return $&
           (offset pair 0). So we set logical_paren to 1 when we should return
           $&, otherwise we set it to 0.

           This allows us to simply add logical_nparens to logical_paren to
           compute the number of elements we are going to return.

           In the loop init we "not" it with: logical_paren = !logical_paren
           which results in it being 0 inside the loop when we want to return
           $&, and results in it being 1 when we want to return the parens.
           Thus we either loop over 1..logical_nparens, or just over 0.

           This is an elegant way to do this code-wise, but is super devious
           and potentially confusing. When I first saw this logic I thought
           "WTF?". But it makes sense after you poke it a while.

           Frankly I probably would have done it differently, but it works so
           I am leaving it. - Yves */
        I32 logical_paren = (global && !logical_nparens) ? 1 : 0;
        I32 *l2p = RXp_LOGICAL_TO_PARNO(prog);
        /* This is used to step through the physical parens associated
           with a given logical paren. */
        I32 *p2l_next = RXp_PARNO_TO_LOGICAL_NEXT(prog);

        rpp_extend(logical_nparens + logical_paren);    /* devious code ... */
        EXTEND_MORTAL(logical_nparens + logical_paren); /* ... see above */

        /* Loop over the logical parens in the pattern. This may not
           correspond to the actual paren checked, as branch reset may
           mean that there is more than one paren "behind" the logical
           parens. Eg, in /(?|(a)|(b))/ there are two parens, but one
           logical paren. */
        for (logical_paren = !logical_paren;
             logical_paren <= logical_nparens;
             logical_paren++)
        {
            /* Now convert the logical_paren to the physical parens which
               are "behind" it. If branch reset was not used, then
               physical_paren and logical_paren are the same as each other
               and we will only perform one iteration of the loop. */
            I32 phys_paren = l2p ? l2p[logical_paren] : logical_paren;
            SSize_t offs_start, offs_end;
            /* We check the loop invariants below and break out of the loop
               explicitly if our checks fail, so we use while (1) here to
               avoid double testing a conditional. */
            while (1) {
                /* Check end offset first, as the start might be >=0 even
                   though the end is -1, so testing the end first helps
                   us avoid the start check.  Really we should be able to
                   get away with ONLY testing the end, but testing both
                   doesn't hurt much and preserves sanity. */
                if (((offs_end   = RXp_OFFS_END(prog, phys_paren))   != -1) &&
                    ((offs_start = RXp_OFFS_START(prog, phys_paren)) != -1))
                {
                    const SSize_t len = offs_end - offs_start;
                    const char * const s = offs_start + truebase;
                    if ( UNLIKELY( len < 0 || len > strend - s) ) {
                        DIE(aTHX_ "panic: pp_match start/end pointers, paren=%" I32df ", "
                            "start=%zd, end=%zd, s=%p, strend=%p, len=%zd",
                            phys_paren, offs_start, offs_end, s, strend, len);
                    }
                    rpp_push_1(newSVpvn_flags(s, len,
                        (DO_UTF8(TARG))
                        ? SVf_UTF8|SVs_TEMP
                        : SVs_TEMP)
                    );
                    break;
                } else if (!p2l_next || !(phys_paren = p2l_next[phys_paren])) {
                    /* Either logical_paren and phys_paren are the same and
                       we won't have a p2l_next, or they aren't the same (and
                       we do have a p2l_next) but we have exhausted the list
                       of physical parens associated with this logical paren.
                       Either way we are done, and we can push undef and break
                       out of the loop. */
                    rpp_push_1(sv_newmortal());
                    break;
                }
            }
        }
        if (global) {
            curpos = (UV)RXp_OFFS_END(prog,0);
            had_zerolen = RXp_ZERO_LEN(prog);
            r_flags |= REXEC_IGNOREPOS | REXEC_NOT_FIRST;
            goto play_it_again;
        }
        LEAVE_SCOPE(oldsave);
        goto ret_list;
    }
    NOT_REACHED; /* NOTREACHED */

  nope:
    if (global && !(dynpm->op_pmflags & PMf_CONTINUE)) {
        if (!mg)
            mg = mg_find_mglob(TARG);
        if (mg)
            mg->mg_len = -1;
    }
    LEAVE_SCOPE(oldsave);
    if (gimme != G_LIST) {
        if (sp_base)
            rpp_popfree_1(); /* free arg */
        rpp_push_IMM(&PL_sv_no);
        return NORMAL;
    }

  ret_list:
    /* return when in list context (i.e. don't push YES/NO, but do return
     * a (possibly empty) list of matches */
    if (sp_base) {
        /* need to free the original argument and shift any results down
         * by one */
        SSize_t nitems = PL_stack_sp - (PL_stack_base + sp_base);
#ifdef PERL_RC_STACK
        SV *old_sv = PL_stack_sp[-nitems];
#endif
        if (nitems)
            Move(PL_stack_sp - nitems + 1,
                 PL_stack_sp - nitems,    nitems, SV*);
        PL_stack_sp--;
#ifdef PERL_RC_STACK
        SvREFCNT_dec_NN(old_sv);
#endif
    }

    return NORMAL;
}


/* Perl_do_readline(): implement <$fh>, readline($fh) and glob('*.h')
 *
 * This function is tail-called by pp_readline(), pp_rcatline() and
 * pp_glob(), and it may check PL_op's op_type and op_flags as
 * appropriate.
 *
 * For file reading:
 *    It reads the line(s) from PL_last_in_gv.
 *    It returns a list of lines, or in scalar context, reads one line into
 *       targ (or if OPf_STACKED, into the top SV on the stack), and
 *       returns that. (If OP_RCATLINE, concats rather than sets).
 *
 *    So it normally expects zero args, or one arg when the OPf_STACKED
 *    optimisation is present.
 *
 * For file globbing:
 *    Note that we don't normally reach here: we only get here if perl is
 *    built with PERL_EXTERNAL_GLOB, which is normally only when
 *    building miniperl.
 *
 *    Expects one arg, which is the pattern string (e.g. '*.h').
 *    The caller sets PL_last_in_gv to a plain GV that just has a new
 *    IO::File PVIO attached. That PVIO is used to attach a pipe file
 *    handle to when an external glob is being run in scalar context,
 *    so the pipe is available on subsequent iterations.
 *
 * Handles tied IO magic, but not overloading - that's the caller's
 * responsibility.
 *
 * Handles the *ARGV filehandle specially, to do all the <> wizardry.
 *
 * In summary: on entry, the stack has zero or one items pushed, and
 * looks like:
 *
 *  -       when OP_READLINE without OPf_STACKED
 *  target  when OP_READLINE with    OPf_STACKED, or when OP_RCATLINE
 *  '*.h'   when OP_GLOB
 */

OP *
Perl_do_readline(pTHX)
{

    const I32 type = PL_op->op_type;

    /* only readline/rcatline can have the STACKED optimisation,
     * and rcatline *always* has it */
    if (PL_op->op_flags & OPf_STACKED) {
        assert(type != OP_GLOB);
        assert(GIMME_V == G_SCALAR);
    }
    if (type == OP_RCATLINE)
        assert(PL_op->op_flags & OPf_STACKED);

    const U8 gimme = GIMME_V;
    SV *targ  = (gimme == G_SCALAR)
                    ? (PL_op->op_flags & OPf_STACKED)
                        ? *PL_stack_sp
                        : PAD_SV(PL_op->op_targ)
                    : NULL;
    SV *sv;
    STRLEN tmplen = 0;
    STRLEN offset;
    PerlIO *fp;
    IO * const io = GvIO(PL_last_in_gv);

    /* process tied file handle if present */

    if (io) {
        const MAGIC *const mg = SvTIED_mg((const SV *)io, PERL_MAGIC_tiedscalar);
        if (mg) {
            /* not possible for the faked-up IO passed by an OP_GLOB to be
             * tied */
            assert(type != OP_GLOB);
            /* OPf_STACKED only applies when in scalar context */
            assert(!(gimme != G_SCALAR && (PL_op->op_flags & OPf_STACKED)));

            /* tied_method() frees everything currently above the passed
             * mark, and returns any values at mark[1] onwards */
            Perl_tied_method(aTHX_ SV_CONST(READLINE),
                /* mark => */ PL_stack_sp,
                              MUTABLE_SV(io), mg, gimme, 0);

            if (gimme == G_SCALAR) {
                SvSetSV_nosteal(targ, *PL_stack_sp);
                SvSETMAGIC(targ);
                if (PL_op->op_flags & OPf_STACKED) {
                    /* free the tied method call's return value */
                    rpp_popfree_1();
                    assert(*PL_stack_sp == targ);
                }
                else
                    rpp_replace_1_1(targ);
            }
            else
                /* no targ to pop off the stack - any returned values
                 * are in the right place in the stack */
                assert(!(PL_op->op_flags & OPf_STACKED));

            return NORMAL;
        }
    }

    fp = NULL;

    /* handle possible *ARGV, and check for read on write-only FH */

    if (io) {
        fp = IoIFP(io);
        if (fp) {
            if (IoTYPE(io) == IoTYPE_WRONLY)
                report_wrongway_fh(PL_last_in_gv, '>');
        }
        else {
            if (IoFLAGS(io) & IOf_ARGV) {
                if (IoFLAGS(io) & IOf_START) {
                    IoLINES(io) = 0;
                    if (av_count(GvAVn(PL_last_in_gv)) == 0) {
                        IoFLAGS(io) &= ~IOf_START;
                        do_open6(PL_last_in_gv, "-", 1, NULL, NULL, 0);
                        SvTAINTED_off(GvSVn(PL_last_in_gv)); /* previous tainting irrelevant */
                        sv_setpvs(GvSVn(PL_last_in_gv), "-");
                        SvSETMAGIC(GvSV(PL_last_in_gv));
                        fp = IoIFP(io);
                        goto have_fp;
                    }
                }
                fp = nextargv(PL_last_in_gv, PL_op->op_flags & OPf_SPECIAL);
                if (!fp) { /* Note: fp != IoIFP(io) */
                    (void)do_close(PL_last_in_gv, FALSE); /* now it does*/
                }
            }
            else if (type == OP_GLOB) {
                fp = Perl_start_glob(aTHX_ *PL_stack_sp, io);
                rpp_popfree_1_NN();
            }
        }
    }

    /* handle bad file handle */

    if (!fp) {
        if ((!io || !(IoFLAGS(io) & IOf_START))
            && ckWARN(WARN_CLOSED)
            && type != OP_GLOB)
        {
            report_evil_fh(PL_last_in_gv);
        }

        if (gimme == G_SCALAR) {
            /* undef targ, and return that undefined value */
            if (type != OP_RCATLINE)
                sv_set_undef(targ);
            if (!(PL_op->op_flags & OPf_STACKED))
                rpp_push_1(targ);
        }
        return NORMAL;
    }

  have_fp:

    /* prepare targ to have a string assigned to it */

    if (gimme == G_SCALAR) {
        sv = targ;
        if (type == OP_RCATLINE && SvGMAGICAL(sv))
            mg_get(sv);

        if (SvROK(sv)) {
            if (type == OP_RCATLINE)
                SvPV_force_nomg_nolen(sv);
            else
                sv_unref(sv);
        }
        else if (isGV_with_GP(sv)) {
            SvPV_force_nomg_nolen(sv);
        }

        SvUPGRADE(sv, SVt_PV);
        tmplen = SvLEN(sv);	/* remember if already alloced */
        if (!tmplen && !SvREADONLY(sv) && !SvIsCOW(sv)) {
            /* try short-buffering it. Please update t/op/readline.t
             * if you change the growth length.
             */
            Sv_Grow(sv, 80);
        }

        offset = 0;
        if (type == OP_RCATLINE && SvOK(sv)) {
            if (!SvPOK(sv)) {
                SvPV_force_nomg_nolen(sv);
            }
            offset = SvCUR(sv);
        }
    }
    else {
        /* XXX on RC builds, push on stack rather than mortalize ? */
        sv = newSV_type_mortal(SVt_PV);
        sv_grow_fresh(sv, 81);
        offset = 0;
    }

    /* This should not be marked tainted if the fp is marked clean */
#define MAYBE_TAINT_LINE(io, sv) \
    if (!(IoFLAGS(io) & IOf_UNTAINT)) { \
        TAINT;				\
        SvTAINTED_on(sv);		\
    }

/* delay EOF state for a snarfed empty file */
#define SNARF_EOF(gimme,rs,io,sv) \
    (gimme != G_SCALAR || SvCUR(sv)					\
     || (IoFLAGS(io) & IOf_NOLINE) || !RsSNARF(rs))

    /* create one or more lines, or (if OP_GLOB), pathnames */

    for (;;) {
        if (!sv_gets(sv, fp, offset)
            && (type == OP_GLOB
                || SNARF_EOF(gimme, PL_rs, io, sv)
                || PerlIO_error(fp)))
        {
            if (IoFLAGS(io) & IOf_ARGV) {
                fp = nextargv(PL_last_in_gv, PL_op->op_flags & OPf_SPECIAL);
                if (fp) {
                    continue;
                }
                (void)do_close(PL_last_in_gv, FALSE);
            }
            else if (type == OP_GLOB) {
                /* clear any errors here so we only fail on the pclose()
                   failing, which should only happen on the child
                   failing
                */
                PerlIO_clearerr(fp);
                if (!do_close(PL_last_in_gv, FALSE)) {
                    ck_warner(packWARN(WARN_GLOB),
                              "glob failed (child exited with status %d%s)",
                              (int)(STATUS_CURRENT >> 8),
                              (STATUS_CURRENT & 0x80) ? ", core dumped" : "");
                }
            }

            if (gimme == G_SCALAR) {
                if (type != OP_RCATLINE) {
                    SV_CHECK_THINKFIRST_COW_DROP(targ);
                    SvOK_off(targ);
                }
                /* targ not already there? */
                if (!(PL_op->op_flags & OPf_STACKED))
                    rpp_push_1(targ);
            }
            else if (PL_op->op_flags & OPf_STACKED)
                rpp_popfree_1_NN();

            MAYBE_TAINT_LINE(io, sv);
            return NORMAL;
        }

        MAYBE_TAINT_LINE(io, sv);
        IoLINES(io)++;
        IoFLAGS(io) |= IOf_NOLINE;
        SvSETMAGIC(sv);
        rpp_extend(1);
        if (PL_op->op_flags & OPf_STACKED) {
            /* push sv while keeping targ above it, so targ doesn't get
             * freed */
            assert(*PL_stack_sp == targ);
            PL_stack_sp[1] = targ;
            *PL_stack_sp++ = NULL;
            rpp_replace_at(PL_stack_sp - 1, sv);
        }
        else 
            rpp_push_1(sv);

        if (type == OP_GLOB) {
            const char *t1;
            Stat_t statbuf;

            /* chomp(sv) */
            if (SvCUR(sv) > 0 && SvCUR(PL_rs) > 0) {
                char * const tmps = SvEND(sv) - 1;
                if (*tmps == *SvPVX_const(PL_rs)) {
                    *tmps = '\0';
                    SvCUR_set(sv, SvCUR(sv) - 1);
                }
            }

            /* find longest substring of sv up to first metachar */
            for (t1 = SvPVX_const(sv); *t1; t1++) {
#ifdef __VMS
                if (memCHRs("*%?", *t1))
#else
                if (memCHRs("$&*(){}[]'\";\\|?<>~`", *t1))
#endif
                        break;
            }

            if (*t1 && PerlLIO_lstat(SvPVX_const(sv), &statbuf) < 0) {
                /* Unmatched wildcard?  Chuck it... */
                /* no need to worry about targ still on top of stack */
                assert(!(PL_op->op_flags & OPf_STACKED));
                rpp_popfree_1();
                continue;
            }
        } else if (SvUTF8(sv)) { /* OP_READLINE, OP_RCATLINE */
             /* check line if valid Unicode */
             if (ckWARN(WARN_UTF8)) {
                const U8 * const s = (const U8*)SvPVX_const(sv) + offset;
                const STRLEN len = SvCUR(sv) - offset;
                const U8 *f;

                if (!is_utf8_string_loc(s, len, &f))
                    /* Emulate :encoding(utf8) warning in the same case. */
                    warner(packWARN(WARN_UTF8),
                           "utf8 \"\\x%02X\" does not map to Unicode",
                           f < (U8*)SvEND(sv) ? *f : 0);
             }
        }

        if (gimme == G_LIST) {
            if (SvLEN(sv) - SvCUR(sv) > 20) {
                SvPV_shrink_to_cur(sv);
            }
            /* XXX on RC builds, push on stack rather than mortalize ? */
            sv = newSV_type_mortal(SVt_PV);
            sv_grow_fresh(sv, 81);
            continue;
        }

        if (gimme == G_SCALAR && !tmplen && SvLEN(sv) - SvCUR(sv) > 80) {
            /* try to reclaim a bit of scalar space (only on 1st alloc) */
            const STRLEN new_len
                = SvCUR(sv) < 60 ? 80 : SvCUR(sv)+40; /* allow some slop */
            SvPV_renew(sv, new_len);
        }


        if (PL_op->op_flags & OPf_STACKED)
            rpp_popfree_1_NN(); /* finally remove targ */
        /* return sv, which was recently pushed onto the stack */
        return NORMAL;
    } /* for (;;) */
}


PP(pp_helem)
{
    HE* he;
    SV **svp;
    SV * const keysv = PL_stack_sp[0];
    HV * const hv = MUTABLE_HV(PL_stack_sp[-1]);
    const U32 lval = PL_op->op_flags & OPf_MOD || LVRET;
    const U32 defer = PL_op->op_private & OPpLVAL_DEFER;
    SV *sv;
    const bool localizing = PL_op->op_private & OPpLVAL_INTRO;
    bool preeminent = TRUE;
    SV *retsv;

    if (SvTYPE(hv) != SVt_PVHV) {
        retsv = &PL_sv_undef;
        goto ret;
    }

    if (localizing) {
        /* Try to preserve the existence of a tied hash
         * element by using EXISTS and DELETE if possible.
         * Fall back to FETCH and STORE otherwise. */
        if (SvCANEXISTDELETE(hv))
            preeminent = hv_exists_ent(hv, keysv, 0);
    }

    he = hv_fetch_ent(hv, keysv, lval && !defer, 0);
    svp = he ? &HeVAL(he) : NULL;
    if (lval) {
        if (!svp || !*svp || *svp == &PL_sv_undef) {
            SV* lv;
            SV* key2;
            if (!defer) {
                DIE(aTHX_ PL_no_helem_sv, SVfARG(keysv));
            }
            lv = newSV_type_mortal(SVt_PVLV);
            LvTYPE(lv) = 'y';
            sv_magic(lv, key2 = newSVsv(keysv), PERL_MAGIC_defelem, NULL, 0);
            SvREFCNT_dec_NN(key2);	/* sv_magic() increments refcount */
            LvTARG(lv) = SvREFCNT_inc_simple_NN(hv);
            LvTARGLEN(lv) = 1;
            retsv = lv;
            goto ret;
        }

        if (localizing) {
            if (HvNAME_get(hv) && isGV_or_RVCV(*svp))
                save_gp(MUTABLE_GV(*svp), !(PL_op->op_flags & OPf_SPECIAL));
            else if (preeminent)
                save_helem_flags(hv, keysv, svp,
                     (PL_op->op_flags & OPf_SPECIAL) ? 0 : SAVEf_SETMAGIC);
            else
                SAVEHDELETE(hv, keysv);
        }
        else if (PL_op->op_private & OPpDEREF) {
            retsv = vivify_ref(*svp, PL_op->op_private & OPpDEREF);
            goto ret;;
        }
    }
    sv = (svp && *svp ? *svp : &PL_sv_undef);
    /* Originally this did a conditional C<sv = sv_mortalcopy(sv)>; this
     * was to make C<local $tied{foo} = $tied{foo}> possible.
     * However, it seems no longer to be needed for that purpose, and
     * introduced a new bug: stuff like C<while ($hash{taintedval} =~ /.../g>
     * would loop endlessly since the pos magic is getting set on the
     * mortal copy and lost. However, the copy has the effect of
     * triggering the get magic, and losing it altogether made things like
     * c<$tied{foo};> in void context no longer do get magic, which some
     * code relied on. Also, delayed triggering of magic on @+ and friends
     * meant the original regex may be out of scope by now. So as a
     * compromise, do the get magic here. (The MGf_GSKIP flag will stop it
     * being called too many times). */
    if (!lval && SvRMAGICAL(hv) && SvGMAGICAL(sv))
        mg_get(sv);
    retsv = sv;

  ret:
    rpp_replace_2_1_NN(retsv);
    return NORMAL;
}


/* a stripped-down version of Perl_softref2xv() for use by
 * pp_multideref(), which doesn't use PL_op->op_flags */

STATIC GV *
S_softref2xv_lite(pTHX_ SV *const sv, const char *const what,
                const svtype type)
{
    if (PL_op->op_private & HINT_STRICT_REFS) {
        if (SvOK(sv))
            die(PL_no_symref_sv, sv,
                     (SvPOKp(sv) && SvCUR(sv)>32 ? "..." : ""), what);
        else
            die(PL_no_usym, what);
    }
    if (!SvOK(sv))
        die(PL_no_usym, what);
    return gv_fetchsv_nomg(sv, GV_ADD, type);
}


/* Handle one or more aggregate derefs and array/hash indexings, e.g.
 * $h->{foo}  or  $a[0]{$key}[$i]  or  f()->[1]
 *
 * op_aux points to an array of unions of UV / IV / SV* / PADOFFSET.
 * Each of these either contains a set of actions, or an argument, such as
 * an IV to use as an array index, or a lexical var to retrieve.
 * Several actions are stored per UV; we keep shifting new actions off the
 * one UV, and only reload when it becomes zero.
 */

PP(pp_multideref)
{
    SV *sv = NULL; /* init to avoid spurious 'may be used uninitialized' */
    UNOP_AUX_item *items = cUNOP_AUXx(PL_op)->op_aux;
    UV actions = items->uv;

    assert(actions);
    /* this tells find_uninit_var() where we're up to */
    PL_multideref_pc = items;
    bool replace = FALSE;

    while (1) {
        /* there are three main classes of action; the first retrieves
         * the initial AV or HV from a variable or the stack; the second
         * does the equivalent of an unrolled (/DREFAV, rv2av, aelem),
         * the third an unrolled (/DREFHV, rv2hv, helem).
         */
        switch (actions & MDEREF_ACTION_MASK) {

        case MDEREF_reload:
            actions = (++items)->uv;
            continue;

        case MDEREF_AV_padav_aelem:                 /* $lex[...] */
            sv = PAD_SVl((++items)->pad_offset);
            goto do_AV_aelem;

        case MDEREF_AV_gvav_aelem:                  /* $pkg[...] */
            sv = UNOP_AUX_item_sv(++items);
            assert(isGV_with_GP(sv));
            sv = (SV*)GvAVn((GV*)sv);
            goto do_AV_aelem;

        case MDEREF_AV_pop_rv2av_aelem:             /* expr->[...] */
            {
                sv = *PL_stack_sp;
                replace = TRUE;
                goto do_AV_rv2av_aelem;
            }

        case MDEREF_AV_gvsv_vivify_rv2av_aelem:     /* $pkg->[...] */
            sv = UNOP_AUX_item_sv(++items);
            assert(isGV_with_GP(sv));
            sv = GvSVn((GV*)sv);
            goto do_AV_vivify_rv2av_aelem;

        case MDEREF_AV_padsv_vivify_rv2av_aelem:     /* $lex->[...] */
            sv = PAD_SVl((++items)->pad_offset);
            /* FALLTHROUGH */

        do_AV_vivify_rv2av_aelem:
        case MDEREF_AV_vivify_rv2av_aelem:           /* vivify, ->[...] */
            /* this is the OPpDEREF action normally found at the end of
             * ops like aelem, helem, rv2sv */
            sv = vivify_ref(sv, OPpDEREF_AV);
            /* FALLTHROUGH */

        do_AV_rv2av_aelem:
            /* this is basically a copy of pp_rv2av when it just has the
             * sKR/1 flags */
            SvGETMAGIC(sv);
            if (LIKELY(SvROK(sv))) {
                if (UNLIKELY(SvAMAGIC(sv))) {
                    sv = amagic_deref_call(sv, to_av_amg);
                }
                sv = SvRV(sv);
                if (UNLIKELY(SvTYPE(sv) != SVt_PVAV))
                    DIE(aTHX_ "Not an ARRAY reference");
            }
            else if (SvTYPE(sv) != SVt_PVAV) {
                if (!isGV_with_GP(sv))
                    sv = (SV*)S_softref2xv_lite(aTHX_ sv, "an ARRAY", SVt_PVAV);
                sv = MUTABLE_SV(GvAVn((GV*)sv));
            }
            /* FALLTHROUGH */

        do_AV_aelem:
            {
                /* retrieve the key; this may be either a lexical or package
                 * var (whose index/ptr is stored as an item) or a signed
                 * integer constant stored as an item.
                 */
                SV *elemsv;
                IV elem = 0; /* to shut up stupid compiler warnings */


                assert(SvTYPE(sv) == SVt_PVAV);

                switch (actions & MDEREF_INDEX_MASK) {
                case MDEREF_INDEX_none:
                    goto finish;
                case MDEREF_INDEX_const:
                    elem  = (++items)->iv;
                    break;
                case MDEREF_INDEX_padsv:
                    elemsv = PAD_SVl((++items)->pad_offset);
                    goto check_elem;
                case MDEREF_INDEX_gvsv:
                    elemsv = UNOP_AUX_item_sv(++items);
                    assert(isGV_with_GP(elemsv));
                    elemsv = GvSVn((GV*)elemsv);
                check_elem:
                    if (UNLIKELY(SvROK(elemsv) && !SvGAMAGIC(elemsv)
                                            && ckWARN(WARN_MISC)))
                        warner(packWARN(WARN_MISC),
                               "Use of reference \"%" SVf "\" as array index",
                               SVfARG(elemsv));
                    /* the only time that S_find_uninit_var() needs this
                     * is to determine which index value triggered the
                     * undef warning. So just update it here. Note that
                     * since we don't save and restore this var (e.g. for
                     * tie or overload execution), its value will be
                     * meaningless apart from just here */
                    PL_multideref_pc = items;
                    elem = SvIV(elemsv);
                    break;
                }


                /* this is basically a copy of pp_aelem with OPpDEREF skipped */

                if (!(actions & MDEREF_FLAG_last)) {
                    SV** svp = av_fetch((AV*)sv, elem, 1);
                    if (!svp || ! (sv=*svp))
                        DIE(aTHX_ PL_no_aelem, elem);
                    break;
                }

                if (PL_op->op_private &
                    (OPpMULTIDEREF_EXISTS|OPpMULTIDEREF_DELETE))
                {
                    if (PL_op->op_private & OPpMULTIDEREF_EXISTS) {
                        sv = av_exists((AV*)sv, elem) ? &PL_sv_yes : &PL_sv_no;
                    }
                    else {
                        I32 discard = (GIMME_V == G_VOID) ? G_DISCARD : 0;
                        sv = av_delete((AV*)sv, elem, discard);
                        if (discard)
                            return NORMAL;
                        if (!sv)
                            sv = &PL_sv_undef;
                    }
                }
                else {
                    const U32 lval = PL_op->op_flags & OPf_MOD || LVRET;
                    const U32 defer = PL_op->op_private & OPpLVAL_DEFER;
                    const bool localizing = PL_op->op_private & OPpLVAL_INTRO;
                    bool preeminent = TRUE;
                    AV *const av = (AV*)sv;
                    SV** svp;

                    if (UNLIKELY(localizing)) {
                        /* Try to preserve the existence of a tied array
                         * element by using EXISTS and DELETE if possible.
                         * Fall back to FETCH and STORE otherwise. */
                        if (SvCANEXISTDELETE(av))
                            preeminent = av_exists(av, elem);
                    }

                    svp = av_fetch(av, elem, lval && !defer);

                    if (lval) {
                        if (!svp || !(sv = *svp)) {
                            IV len;
                            if (!defer)
                                DIE(aTHX_ PL_no_aelem, elem);
                            len = av_top_index(av);
                            /* Resolve a negative index that falls within
                             * the array.  Leave it negative it if falls
                             * outside the array.  */
                             if (elem < 0 && len + elem >= 0)
                                 elem = len + elem;
                             if (elem >= 0 && elem <= len)
                                 /* Falls within the array.  */
                                 sv = av_nonelem(av,elem);
                             else
                                 /* Falls outside the array.  If it is neg-
                                    ative, magic_setdefelem will use the
                                    index for error reporting.  */
                                sv = sv_2mortal(newSVavdefelem(av,elem,1));
                        }
                        else {
                            if (UNLIKELY(localizing)) {
                                if (preeminent) {
                                    save_aelem(av, elem, svp);
                                    sv = *svp; /* may have changed */
                                }
                                else
                                    SAVEADELETE(av, elem);
                            }
                        }
                    }
                    else {
                        sv = (svp ? *svp : &PL_sv_undef);
                        /* see note in pp_helem() */
                        if (SvRMAGICAL(av) && SvGMAGICAL(sv))
                            mg_get(sv);
                    }
                }

            }
          finish:
            {
                if (replace)
                    rpp_replace_1_1_NN(sv);
                else
                    rpp_xpush_1(sv);
                return NORMAL;
            }
            /* NOTREACHED */




        case MDEREF_HV_padhv_helem:                 /* $lex{...} */
            sv = PAD_SVl((++items)->pad_offset);
            goto do_HV_helem;

        case MDEREF_HV_gvhv_helem:                  /* $pkg{...} */
            sv = UNOP_AUX_item_sv(++items);
            assert(isGV_with_GP(sv));
            sv = (SV*)GvHVn((GV*)sv);
            goto do_HV_helem;

        case MDEREF_HV_pop_rv2hv_helem:             /* expr->{...} */
            {
                sv = *PL_stack_sp;
                replace = TRUE;
                goto do_HV_rv2hv_helem;
            }

        case MDEREF_HV_gvsv_vivify_rv2hv_helem:     /* $pkg->{...} */
            sv = UNOP_AUX_item_sv(++items);
            assert(isGV_with_GP(sv));
            sv = GvSVn((GV*)sv);
            goto do_HV_vivify_rv2hv_helem;

        case MDEREF_HV_padsv_vivify_rv2hv_helem:    /* $lex->{...} */
            sv = PAD_SVl((++items)->pad_offset);
            /* FALLTHROUGH */

        do_HV_vivify_rv2hv_helem:
        case MDEREF_HV_vivify_rv2hv_helem:           /* vivify, ->{...} */
            /* this is the OPpDEREF action normally found at the end of
             * ops like aelem, helem, rv2sv */
            sv = vivify_ref(sv, OPpDEREF_HV);
            /* FALLTHROUGH */

        do_HV_rv2hv_helem:
            /* this is basically a copy of pp_rv2hv when it just has the
             * sKR/1 flags (and pp_rv2hv is aliased to pp_rv2av) */

            SvGETMAGIC(sv);
            if (LIKELY(SvROK(sv))) {
                if (UNLIKELY(SvAMAGIC(sv))) {
                    sv = amagic_deref_call(sv, to_hv_amg);
                }
                sv = SvRV(sv);
                if (UNLIKELY(SvTYPE(sv) != SVt_PVHV))
                    DIE(aTHX_ "Not a HASH reference");
            }
            else if (SvTYPE(sv) != SVt_PVHV) {
                if (!isGV_with_GP(sv))
                    sv = (SV*)S_softref2xv_lite(aTHX_ sv, "a HASH", SVt_PVHV);
                sv = MUTABLE_SV(GvHVn((GV*)sv));
            }
            /* FALLTHROUGH */

        do_HV_helem:
            {
                /* retrieve the key; this may be either a lexical / package
                 * var or a string constant, whose index/ptr is stored as an
                 * item
                 */
                SV *keysv = NULL; /* to shut up stupid compiler warnings */

                assert(SvTYPE(sv) == SVt_PVHV);

                switch (actions & MDEREF_INDEX_MASK) {
                case MDEREF_INDEX_none:
                    goto finish;

                case MDEREF_INDEX_const:
                    keysv = UNOP_AUX_item_sv(++items);
                    break;

                case MDEREF_INDEX_padsv:
                    keysv = PAD_SVl((++items)->pad_offset);
                    break;

                case MDEREF_INDEX_gvsv:
                    keysv = UNOP_AUX_item_sv(++items);
                    keysv = GvSVn((GV*)keysv);
                    break;
                }

                /* see comment above about setting this var */
                PL_multideref_pc = items;


                /* ensure that candidate CONSTs have been HEKified */
                assert(   ((actions & MDEREF_INDEX_MASK) != MDEREF_INDEX_const)
                       || SvTYPE(keysv) >= SVt_PVMG
                       || !SvOK(keysv)
                       || SvROK(keysv)
                       || SvIsCOW_shared_hash(keysv));

                /* this is basically a copy of pp_helem with OPpDEREF skipped */

                if (!(actions & MDEREF_FLAG_last)) {
                    HE *he = hv_fetch_ent((HV*)sv, keysv, 1, 0);
                    if (!he || !(sv=HeVAL(he)) || sv == &PL_sv_undef)
                        DIE(aTHX_ PL_no_helem_sv, SVfARG(keysv));
                    break;
                }

                if (PL_op->op_private &
                    (OPpMULTIDEREF_EXISTS|OPpMULTIDEREF_DELETE))
                {
                    if (PL_op->op_private & OPpMULTIDEREF_EXISTS) {
                        sv = hv_exists_ent((HV*)sv, keysv, 0)
                                                ? &PL_sv_yes : &PL_sv_no;
                    }
                    else {
                        I32 discard = (GIMME_V == G_VOID) ? G_DISCARD : 0;
                        sv = hv_delete_ent((HV*)sv, keysv, discard, 0);
                        if (discard)
                            return NORMAL;
                        if (!sv)
                            sv = &PL_sv_undef;
                    }
                }
                else {
                    const U32 lval = PL_op->op_flags & OPf_MOD || LVRET;
                    const U32 defer = PL_op->op_private & OPpLVAL_DEFER;
                    const bool localizing = PL_op->op_private & OPpLVAL_INTRO;
                    bool preeminent = TRUE;
                    SV **svp;
                    HV * const hv = (HV*)sv;
                    HE* he;

                    if (UNLIKELY(localizing)) {
                        /* Try to preserve the existence of a tied hash
                         * element by using EXISTS and DELETE if possible.
                         * Fall back to FETCH and STORE otherwise. */
                        if (SvCANEXISTDELETE(hv))
                            preeminent = hv_exists_ent(hv, keysv, 0);
                    }

                    he = hv_fetch_ent(hv, keysv, lval && !defer, 0);
                    svp = he ? &HeVAL(he) : NULL;


                    if (lval) {
                        if (!svp || !(sv = *svp) || sv == &PL_sv_undef) {
                            SV* lv;
                            SV* key2;
                            if (!defer)
                                DIE(aTHX_ PL_no_helem_sv, SVfARG(keysv));
                            lv = newSV_type_mortal(SVt_PVLV);
                            LvTYPE(lv) = 'y';
                            sv_magic(lv, key2 = newSVsv(keysv),
                                                PERL_MAGIC_defelem, NULL, 0);
                            /* sv_magic() increments refcount */
                            SvREFCNT_dec_NN(key2);
                            LvTARG(lv) = SvREFCNT_inc_simple_NN(hv);
                            LvTARGLEN(lv) = 1;
                            sv = lv;
                        }
                        else {
                            if (localizing) {
                                if (HvNAME_get(hv) && isGV_or_RVCV(sv))
                                    save_gp(MUTABLE_GV(sv),
                                        !(PL_op->op_flags & OPf_SPECIAL));
                                else if (preeminent) {
                                    save_helem_flags(hv, keysv, svp,
                                         (PL_op->op_flags & OPf_SPECIAL)
                                            ? 0 : SAVEf_SETMAGIC);
                                    sv = *svp; /* may have changed */
                                }
                                else
                                    SAVEHDELETE(hv, keysv);
                            }
                        }
                    }
                    else {
                        sv = (svp && *svp ? *svp : &PL_sv_undef);
                        /* see note in pp_helem() */
                        if (SvRMAGICAL(hv) && SvGMAGICAL(sv))
                            mg_get(sv);
                    }
                }
                goto finish;
            }

        } /* switch */

        actions >>= MDEREF_SHIFT;
    } /* while */
    /* NOTREACHED */
}


PP(pp_iter)
{
    PERL_CONTEXT *cx = CX_CUR();
    SV **itersvp = CxITERVAR(cx);
    const U8 type = CxTYPE(cx);
    U8 pflags = PL_op->op_private;

    /* Classic "for" syntax iterates one-at-a-time.
       Many-at-a-time for loops are only for lexicals declared as part of the
       for loop, and rely on all the lexicals being in adjacent pad slots.

       Curiously, even if the iterator variable is a lexical, the pad offset is
       stored in the targ slot of the ENTERITER op, meaning that targ of this OP
       has always been zero. Hence we can use this op's targ to hold "how many"
       for many-at-a-time. We actually store C<how_many - 1>, so that for the
       case of one-at-a-time we have zero (as before), as this makes all the
       logic of the for loop below much simpler, with all the other
       one-at-a-time cases just falling out of this "naturally". */
    PADOFFSET how_many = PL_op->op_targ;
    PADOFFSET i = 0;

    assert(itersvp);

    for (; i <= how_many; ++i ) {
        SV *oldsv;
        SV *sv;
        AV *av;
        IV ix;
        IV inc;

        switch (type) {

        case CXt_LOOP_LAZYSV: /* string increment */
            {
                SV* cur = cx->blk_loop.state_u.lazysv.cur;
                SV *end = cx->blk_loop.state_u.lazysv.end;
                /* If the maximum is !SvOK(), pp_enteriter substitutes PL_sv_no.
                   It has SvPVX of "" and SvCUR of 0, which is what we want.  */
                STRLEN maxlen = 0;
                const char *max = SvPV_const(end, maxlen);
                bool pad_it = FALSE;
                if (DO_UTF8(end) && IN_UNI_8_BIT)
                    maxlen = sv_len_utf8_nomg(end);
                if (UNLIKELY(SvNIOK(cur) || SvCUR(cur) > maxlen)) {
                    if (LIKELY(!i)) {
                        goto retno;
                    }
                    /* We are looping n-at-a-time and the range isn't a multiple
                       of n, so we fill the rest of the lexicals with undef.
                       This only happens on the last iteration of the loop, and
                       we will have already set up the "terminate next time"
                       condition earlier in this for loop for this call of the
                       ITER op when we set up the lexical corresponding to the
                       last value in the range. Hence we don't goto retno (yet),
                       and just below we don't repeat the setup for "terminate
                       next time". */
                    pad_it = TRUE;
                }

                oldsv = *itersvp;
                /* NB: on the first iteration, oldsv will have a ref count of at
                 * least 2 (one extra from blk_loop.itersave), so the GV or pad
                 * slot will get localised; on subsequent iterations the RC==1
                 * optimisation may kick in and the SV will be reused. */
                if (UNLIKELY(pad_it)) {
                    *itersvp = &PL_sv_undef;
                    SvREFCNT_dec(oldsv);
                }
                else if (oldsv && LIKELY(SvREFCNT(oldsv) == 1 && !SvMAGICAL(oldsv))) {
                    /* safe to reuse old SV */
                    sv_setsv(oldsv, cur);
                }
                else {
                    /* we need a fresh SV every time so that loop body sees a
                     * completely new SV for closures/references to work as
                     * they used to */
                    *itersvp = newSVsv(cur);
                    SvREFCNT_dec(oldsv);
                }

                if (UNLIKELY(pad_it)) {
                    /* We're "beyond the end" of the iterator here, filling the
                       extra lexicals with undef, so we mustn't do anything
                       (further) to the iterator itself at this point.
                       (Observe how the other two blocks modify the iterator's
                       value) */
                }
                else if (strEQ(SvPVX_const(cur), max))
                    sv_setiv(cur, 0); /* terminate next time */
                else
                    sv_inc(cur);
                break;
            }

        case CXt_LOOP_LAZYIV: /* integer increment */
            {
                IV cur = cx->blk_loop.state_u.lazyiv.cur;
                bool pad_it = FALSE;
                if (UNLIKELY(cur > cx->blk_loop.state_u.lazyiv.end)) {
                    if (LIKELY(!i)) {
                        goto retno;
                    }
                    pad_it = TRUE;
                }

                oldsv = *itersvp;
                /* see NB comment above */
                if (UNLIKELY(pad_it)) {
                    *itersvp = &PL_sv_undef;
                    SvREFCNT_dec(oldsv);
                }
                else if (oldsv && LIKELY(SvREFCNT(oldsv) == 1 && !SvMAGICAL(oldsv))) {
                    /* safe to reuse old SV */

                    if (    (SvFLAGS(oldsv) & (SVTYPEMASK|SVf_THINKFIRST|SVf_IVisUV))
                         == SVt_IV) {
                        /* Cheap SvIOK_only().
                         * Assert that flags which SvIOK_only() would test or
                         * clear can't be set, because we're SVt_IV */
                        assert(!(SvFLAGS(oldsv) &
                                 (SVf_OOK|SVf_UTF8|(SVf_OK & ~(SVf_IOK|SVp_IOK)))));
                        SvFLAGS(oldsv) |= (SVf_IOK|SVp_IOK);
                        /* SvIV_set() where sv_any points to head */
                        oldsv->sv_u.svu_iv = cur;

                    }
                    else
                        sv_setiv(oldsv, cur);
                }
                else {
                    /* we need a fresh SV every time so that loop body sees a
                     * completely new SV for closures/references to work as they
                     * used to */
                    *itersvp = newSViv(cur);
                    SvREFCNT_dec(oldsv);
                }

                if (UNLIKELY(pad_it)) {
                    /* We're good (see "We are looping n-at-a-time" comment
                       above). */
                }
                else if (UNLIKELY(cur == IV_MAX)) {
                    /* Handle end of range at IV_MAX */
                    cx->blk_loop.state_u.lazyiv.end = IV_MIN;
                } else
                    ++cx->blk_loop.state_u.lazyiv.cur;
                break;
            }

        case CXt_LOOP_LIST: /* for (1,2,3) */

            assert(OPpITER_REVERSED == 2); /* so inc becomes -1 or 1 */
            inc = (IV)1 - (IV)(pflags & OPpITER_REVERSED);
            ix = (cx->blk_loop.state_u.stack.ix += inc);
            if (UNLIKELY(inc > 0
                         ? ix > cx->blk_oldsp
                         : ix <= cx->blk_loop.state_u.stack.basesp)
                ) {
                if (LIKELY(!i)) {
                    goto retno;
                }

                sv = &PL_sv_undef;
            }
            else {
                sv = PL_stack_base[ix];
            }

            if (UNLIKELY(pflags & OPpITER_INDEXED) && (i == 0)) {
                SvREFCNT_dec(*itersvp);
                /* here ix is really a stack pointer offset; we have to
                 * calculate the real index */
                *itersvp = newSViv(ix - cx->blk_loop.state_u.stack.basesp - 1);

                ++i;
                ++itersvp;
            }

            av = NULL;
            goto loop_ary_common;

        case CXt_LOOP_ARY: /* for (@ary) */

            av = cx->blk_loop.state_u.ary.ary;
            inc = (IV)1 - (IV)(pflags & OPpITER_REVERSED);
            ix = (cx->blk_loop.state_u.ary.ix += inc);
            if (UNLIKELY(inc > 0
                         ? ix > AvFILL(av)
                         : ix < 0)
                ) {
                if (LIKELY(!i)) {
                    goto retno;
                }

                sv = &PL_sv_undef;
            } else if (UNLIKELY(SvRMAGICAL(av))) {
                SV * const * const svp = av_fetch(av, ix, FALSE);
                sv = svp ? *svp : NULL;
            }
            else {
                sv = AvARRAY(av)[ix];
            }

            if (UNLIKELY(pflags & OPpITER_INDEXED) && (i == 0)) {
                SvREFCNT_dec(*itersvp);
                *itersvp = newSViv(ix);

                ++i;
                ++itersvp;
            }

        loop_ary_common:

            if (UNLIKELY(cx->cx_type & CXp_FOR_LVREF)) {
                SvSetMagicSV(*itersvp, sv);
                break;
            }

            if (LIKELY(sv)) {
                if (UNLIKELY(SvIS_FREED(sv))) {
                    *itersvp = NULL;
                    croak("Use of freed value in iteration");
                }
                if (SvPADTMP(sv)) {
                    sv = newSVsv(sv);
                }
                else {
                    SvTEMP_off(sv);
                    SvREFCNT_inc_simple_void_NN(sv);
                }
            }
            else if (av) {
                sv = newSVavdefelem(av, ix, 0);
            }
            else
                sv = &PL_sv_undef;

            oldsv = *itersvp;
            *itersvp = sv;
            SvREFCNT_dec(oldsv);
            break;

        default:
            DIE(aTHX_ "panic: pp_iter, type=%u", CxTYPE(cx));
        }

        /* Only relevant for a many-at-a-time loop: */
        ++itersvp;
    }

    /* Try to bypass pushing &PL_sv_yes and calling pp_and(); instead
     * jump straight to the AND op's op_other */
    assert(PL_op->op_next->op_type == OP_AND);
    if (PL_op->op_next->op_ppaddr == Perl_pp_and) {
        return cLOGOPx(PL_op->op_next)->op_other;
    }
    else {
        /* An XS module has replaced the op_ppaddr, so fall back to the slow,
         * obvious way. */
        /* pp_enteriter should have pre-extended the stack */
        EXTEND_SKIP(PL_stack_sp, 1);
        rpp_push_IMM(&PL_sv_yes);
        return PL_op->op_next;
    }

  retno:
    /* Try to bypass pushing &PL_sv_no and calling pp_and(); instead
     * jump straight to the AND op's op_next */
    assert(PL_op->op_next->op_type == OP_AND);
    /* pp_enteriter should have pre-extended the stack */
    EXTEND_SKIP(PL_stack_sp, 1);
    /* we only need this for the rare case where the OP_AND isn't
     * in void context, e.g. $x = do { for (..) {...} };
     * (or for when an XS module has replaced the op_ppaddr)
     * but it's cheaper to just push it rather than testing first
     */
    rpp_push_IMM(&PL_sv_no);
    if (PL_op->op_next->op_ppaddr == Perl_pp_and) {
        return PL_op->op_next->op_next;
    }
    else {
        /* An XS module has replaced the op_ppaddr, so fall back to the slow,
         * obvious way. */
        return PL_op->op_next;
    }
}


/*
A description of how taint works in pattern matching and substitution.

This is all conditional on NO_TAINT_SUPPORT remaining undefined (the default).
Under NO_TAINT_SUPPORT, taint-related operations should become no-ops.

While the pattern is being assembled/concatenated and then compiled,
PL_tainted will get set (via TAINT_set) if any component of the pattern
is tainted, e.g. /.*$tainted/.  At the end of pattern compilation,
the RXf_TAINTED flag is set on the pattern if PL_tainted is set (via
TAINT_get).  It will also be set if any component of the pattern matches
based on locale-dependent behavior.

When the pattern is copied, e.g. $r = qr/..../, the SV holding the ref to
the pattern is marked as tainted. This means that subsequent usage, such
as /x$r/, will set PL_tainted using TAINT_set, and thus RXf_TAINTED,
on the new pattern too.

RXf_TAINTED_SEEN is used post-execution by the get magic code
of $1 et al to indicate whether the returned value should be tainted.
It is the responsibility of the caller of the pattern (i.e. pp_match,
pp_subst etc) to set this flag for any other circumstances where $1 needs
to be tainted.

The taint behaviour of pp_subst (and pp_substcont) is quite complex.

There are three possible sources of taint
    * the source string
    * the pattern (both compile- and run-time, RXf_TAINTED / RXf_TAINTED_SEEN)
    * the replacement string (or expression under /e)
    
There are four destinations of taint and they are affected by the sources
according to the rules below:

    * the return value (not including /r):
        tainted by the source string and pattern, but only for the
        number-of-iterations case; boolean returns aren't tainted;
    * the modified string (or modified copy under /r):
        tainted by the source string, pattern, and replacement strings;
    * $1 et al:
        tainted by the pattern, and under 'use re "taint"', by the source
        string too;
    * PL_taint - i.e. whether subsequent code (e.g. in a /e block) is tainted:
        should always be unset before executing subsequent code.

The overall action of pp_subst is:

    * at the start, set bits in rxtainted indicating the taint status of
        the various sources.

    * After each pattern execution, update the SUBST_TAINT_PAT bit in
        rxtainted if RXf_TAINTED_SEEN has been set, to indicate that the
        pattern has subsequently become tainted via locale ops.

    * If control is being passed to pp_substcont to execute a /e block,
        save rxtainted in the CXt_SUBST block, for future use by
        pp_substcont.

    * Whenever control is being returned to perl code (either by falling
        off the "end" of pp_subst/pp_substcont, or by entering a /e block),
        use the flag bits in rxtainted to make all the appropriate types of
        destination taint visible; e.g. set RXf_TAINTED_SEEN so that $1
        et al will appear tainted.

pp_match is just a simpler version of the above.

*/

PP(pp_subst)
{
    dTARG;
    PMOP *pm = cPMOP;
    PMOP *rpm = pm;
    char *s;
    char *strend;
    const char *c;
    STRLEN clen;
    SSize_t iters = 0;
    SSize_t maxiters;
    bool once;
    U8 rxtainted = 0; /* holds various SUBST_TAINT_* flag bits.
                        See "how taint works" above */
    char *orig;
    U8 r_flags;
    REGEXP *rx = PM_GETRE(pm);
    regexp *prog = ReANY(rx);
    STRLEN len;
    int force_on_match = 0;
    const I32 oldsave = PL_savestack_ix;
    bool doutf8 = FALSE; /* whether replacement is in utf8 */
#ifdef PERL_ANY_COW
    bool was_cow;
#endif
    SV *nsv = NULL;
    SSize_t sp_offset = 0; /* number of items left on stack */
    SV *dstr;
    SV *retval;

    PERL_ASYNC_CHECK();

    if (pm->op_pmflags & PMf_CONST) {
        /* known replacement string */
        dstr = *PL_stack_sp;
        sp_offset++;
    }
    else
        dstr = NULL;

    if (PL_op->op_flags & OPf_STACKED) {
        /*  expr =~ s///;  */
        TARG = PL_stack_sp[-sp_offset];
        sp_offset++;
    }
    else {
        if (ARGTARG)
            /*  $lex =~ s///;  */
            GETTARGET;
        else {
            /* s///;  */
            TARG = DEFSV;
        }
        if (!sp_offset)
            rpp_extend(1);
    }

    SvGETMAGIC(TARG); /* must come before cow check */
#ifdef PERL_ANY_COW
    /* note that a string might get converted to COW during matching */
    was_cow = cBOOL(SvIsCOW(TARG));
#endif
    if (!(rpm->op_pmflags & PMf_NONDESTRUCT)) {
#ifndef PERL_ANY_COW
        if (SvIsCOW(TARG))
            sv_force_normal_flags(TARG,0);
#endif
        if ((SvREADONLY(TARG)
                || ( ((SvTYPE(TARG) == SVt_PVGV && isGV_with_GP(TARG))
                      || SvTYPE(TARG) > SVt_PVLV)
                     && !(SvTYPE(TARG) == SVt_PVGV && SvFAKE(TARG)))))
            croak_no_modify();
    }

    orig = SvPV_nomg(TARG, len);
    /* note we don't (yet) force the var into being a string; if we fail
     * to match, we leave as-is; on successful match however, we *will*
     * coerce into a string, then repeat the match */
    if (!SvPOKp(TARG) || SvTYPE(TARG) == SVt_PVGV || SvVOK(TARG))
        force_on_match = 1;

    /* only replace once? */
    once = !(rpm->op_pmflags & PMf_GLOBAL);

    /* See "how taint works" above */
    if (TAINTING_get) {
        rxtainted  = (
            (SvTAINTED(TARG) ? SUBST_TAINT_STR : 0)
          | (RXp_ISTAINTED(prog) ? SUBST_TAINT_PAT : 0)
          | ((pm->op_pmflags & PMf_RETAINT) ? SUBST_TAINT_RETAINT : 0)
          | ((  (once && !(rpm->op_pmflags & PMf_NONDESTRUCT))
             || (PL_op->op_private & OPpTRUEBOOL)) ? SUBST_TAINT_BOOLRET : 0));
        TAINT_NOT;
    }

  force_it:
    if (!pm || !orig)
        DIE(aTHX_ "panic: pp_subst, pm=%p, orig=%p", pm, orig);

    strend = orig + len;
    /* We can match twice at each position, once with zero-length,
     * second time with non-zero.
     * Don't handle utf8 specially; we can use length-in-bytes as an
     * upper bound on length-in-characters, and avoid the cpu-cost of
     * computing a tighter bound. */
    maxiters = 2 * len + 10;

    /* handle the empty pattern */
    if (!RX_PRELEN(rx) && PL_curpm && !prog->mother_re) {
        if (PL_curpm == PL_reg_curpm) {
            if (PL_curpm_under) {
                if (PL_curpm_under == PL_reg_curpm) {
                    croak("Infinite recursion via empty pattern");
                } else {
                    pm = PL_curpm_under;
                }
            }
        } else {
            pm = PL_curpm;
        }
        rx = PM_GETRE(pm);
        prog = ReANY(rx);
    }

#ifdef PERL_SAWAMPERSAND
    r_flags = (    RXp_NPARENS(prog)
                || PL_sawampersand
                || (RXp_EXTFLAGS(prog) & (RXf_EVAL_SEEN|RXf_PMf_KEEPCOPY))
                || (rpm->op_pmflags & PMf_KEEPCOPY)
              )
          ? REXEC_COPY_STR
          : 0;
#else
    r_flags = REXEC_COPY_STR;
#endif

    if (!CALLREGEXEC(rx, orig, strend, orig, 0, TARG, NULL, r_flags))
    {
        SV *ret = rpm->op_pmflags & PMf_NONDESTRUCT ? TARG : &PL_sv_no;
        if (dstr)
            rpp_popfree_1_NN(); /* pop replacement string */
        if (PL_op->op_flags & OPf_STACKED)
            rpp_replace_1_1_NN(ret); /* pop LHS of =~ */
        else
            rpp_push_1(ret);
        LEAVE_SCOPE(oldsave);
        return NORMAL;
    }
    PL_curpm = pm;

    /* known replacement string? */
    if (dstr) {
        /* replacement needing upgrading? */
        if (DO_UTF8(TARG) && !doutf8) {
             nsv = sv_newmortal();
             SvSetSV(nsv, dstr);
             sv_utf8_upgrade(nsv);
             c = SvPV_const(nsv, clen);
             doutf8 = TRUE;
        }
        else {
            c = SvPV_const(dstr, clen);
            doutf8 = DO_UTF8(dstr);
        }

        if (UNLIKELY(TAINT_get))
            rxtainted |= SUBST_TAINT_REPL;
    }
    else {
        c = NULL;
        doutf8 = FALSE;
    }
    
    if (c
#ifdef PERL_ANY_COW
        && !was_cow
#endif
        && (SSize_t)clen <= RXp_MINLENRET(prog)
        && (  once
           || !(r_flags & REXEC_COPY_STR)
           || (!SvGMAGICAL(dstr) && !(RXp_EXTFLAGS(prog) & RXf_EVAL_SEEN))
           )
        && !(RXp_EXTFLAGS(prog) & RXf_NO_INPLACE_SUBST)
        && (!doutf8 || SvUTF8(TARG))
        && !(rpm->op_pmflags & PMf_NONDESTRUCT))
    {
        /* known replacement string and can do in-place substitution */

#ifdef PERL_ANY_COW
        /* string might have got converted to COW since we set was_cow */
        if (SvIsCOW(TARG)) {
          if (!force_on_match)
            goto have_a_cow;
          assert(SvVOK(TARG));
        }
#endif
        if (force_on_match) {
            /* redo the first match, this time with the orig var
             * forced into being a string */
            force_on_match = 0;
            orig = SvPV_force_nomg(TARG, len);
            goto force_it;
        }

        if (once) {
            char *d, *m;
            if (RXp_MATCH_TAINTED(prog)) /* run time pattern taint, eg locale */
                rxtainted |= SUBST_TAINT_PAT;
            m = orig + RXp_OFFS_START(prog,0);
            d = orig + RXp_OFFS_END(prog,0);
            s = orig;
            if (m - s > strend - d) {  /* faster to shorten from end */
                SSize_t i;
                if (clen) {
                    Copy(c, m, clen, char);
                    m += clen;
                }
                i = strend - d;
                if (i > 0) {
                    Move(d, m, i, char);
                    m += i;
                }
                *m = '\0';
                SvCUR_set(TARG, m - s);
            }
            else {	/* faster from front */
                SSize_t i = m - s;
                d -= clen;
                if (i > 0)
                    Move(s, d - i, i, char);
                sv_chop(TARG, d-i);
                if (clen)
                    Copy(c, d, clen, char);
            }
            retval = &PL_sv_yes;
            goto ret;
        }
        else {
            char *d, *m;
            d = s = RXp_OFFS_START(prog,0) + orig;
            do {
                SSize_t i;
                if (UNLIKELY(iters++ > maxiters))
                    DIE(aTHX_ "Substitution loop");
                /* run time pattern taint, eg locale */
                if (UNLIKELY(RXp_MATCH_TAINTED(prog)))
                    rxtainted |= SUBST_TAINT_PAT;
                m = RXp_OFFS_START(prog,0) + orig;
                if ((i = m - s)) {
                    if (s != d)
                        Move(s, d, i, char);
                    d += i;
                }
                if (clen) {
                    Copy(c, d, clen, char);
                    d += clen;
                }
                s = RXp_OFFS_END(prog,0) + orig;
            } while (CALLREGEXEC(rx, s, strend, orig,
                                 s == m, /* don't match same null twice */
                                 TARG, NULL,
                     REXEC_NOT_FIRST|REXEC_IGNOREPOS|REXEC_FAIL_ON_UNDERFLOW));
            if (s != d) {
                SSize_t i = strend - s;
                SvCUR_set(TARG, d - SvPVX_const(TARG) + i);
                Move(s, d, i+1, char);		/* include the NUL */
            }
            assert(iters);
            goto ret_iters;
        }
    }
    else {
        /* not known replacement string or can't do in-place substitution) */
        bool first;
        char *m;
        SV *repl;
        if (force_on_match) {
            /* redo the first match, this time with the orig var
             * forced into being a string */
            force_on_match = 0;
            if (rpm->op_pmflags & PMf_NONDESTRUCT) {
                /* I feel that it should be possible to avoid this mortal copy
                   given that the code below copies into a new destination.
                   However, I suspect it isn't worth the complexity of
                   unravelling the C<goto force_it> for the small number of
                   cases where it would be viable to drop into the copy code. */
                TARG = sv_mortalcopy_flags(TARG, SV_GMAGIC|SV_NOSTEAL);
            }
            orig = SvPV_force_nomg(TARG, len);
            goto force_it;
        }
#ifdef PERL_ANY_COW
      have_a_cow:
#endif
        if (RXp_MATCH_TAINTED(prog)) /* run time pattern taint, eg locale */
            rxtainted |= SUBST_TAINT_PAT;
        repl = dstr;
        s = RXp_OFFS_START(prog,0) + orig;
        dstr = newSVpvn_flags(orig, s-orig,
                    SVs_TEMP | (DO_UTF8(TARG) ? SVf_UTF8 : 0));
        if (!c) {
        /* not known replacement string - call out to ops and OP_SUBSTCONT */
            PERL_CONTEXT *cx;
            m = orig;
            /* note that a whole bunch of local vars are saved here for
             * use by pp_substcont: here's a list of them in case you're
             * searching for places in this sub that uses a particular var:
             * iters maxiters r_flags oldsave rxtainted orig dstr targ
             * s m strend rx once */
            CX_PUSHSUBST(cx);
            return cPMOP->op_pmreplrootu.op_pmreplroot;
        }

        /* We get here if it's a known replacement string, but can't
         * substitute in-place */

        first = TRUE;
        do {
            if (UNLIKELY(iters++ > maxiters))
                DIE(aTHX_ "Substitution loop");
            if (UNLIKELY(RXp_MATCH_TAINTED(prog)))
                rxtainted |= SUBST_TAINT_PAT;
            if (RXp_MATCH_COPIED(prog) && RXp_SUBBEG(prog) != orig) {
                char *old_s    = s;
                char *old_orig = orig;
                assert(RXp_SUBOFFSET(prog) == 0);

                orig = RXp_SUBBEG(prog);
                s = orig + (old_s - old_orig);
                strend = s + (strend - old_s);
            }
            m = RXp_OFFS_START(prog,0) + orig;
            sv_catpvn_nomg_maybeutf8(dstr, s, m - s, DO_UTF8(TARG));
            s = RXp_OFFS_END(prog,0) + orig;
            if (first) {
                /* replacement already stringified */
              if (clen)
                sv_catpvn_nomg_maybeutf8(dstr, c, clen, doutf8);
              first = FALSE;
            }
            else {
                sv_catsv(dstr, repl);
            }
            if (once)
                break;
        } while (CALLREGEXEC(rx, s, strend, orig,
                             s == m,    /* Yields minend of 0 or 1 */
                             TARG, NULL,
                    REXEC_NOT_FIRST|REXEC_IGNOREPOS|REXEC_FAIL_ON_UNDERFLOW));
        assert(strend >= s);
        sv_catpvn_nomg_maybeutf8(dstr, s, strend - s, DO_UTF8(TARG));

        if (rpm->op_pmflags & PMf_NONDESTRUCT) {
            /* From here on down we're using the copy, and leaving the original
               untouched.  */
            TARG = dstr;
            retval = dstr;
            goto ret;
        } else {
#ifdef PERL_ANY_COW
            /* The match may make the string COW. If so, brilliant, because
               that's just saved us one malloc, copy and free - the regexp has
               donated the old buffer, and we malloc an entirely new one, rather
               than the regexp malloc()ing a buffer and copying our original,
               only for us to throw it away here during the substitution.  */
            if (SvIsCOW(TARG)) {
                sv_force_normal_flags(TARG, SV_COW_DROP_PV);
            } else
#endif
            {
                SvPV_free(TARG);
            }
            SvPV_set(TARG, SvPVX(dstr));
            SvCUR_set(TARG, SvCUR(dstr));
            SvLEN_set(TARG, SvLEN(dstr));
            SvFLAGS(TARG) |= SvUTF8(dstr);
            SvPV_set(dstr, NULL);
            goto ret_iters;
        }
    }

  ret_iters:
    if (PL_op->op_private & OPpTRUEBOOL)
        retval = &PL_sv_yes;
    else {
        retval = sv_newmortal();
        sv_setiv(retval, iters);
    }

  ret:
    if (dstr)
        rpp_popfree_1_NN(); /* pop replacement string */
    if (PL_op->op_flags & OPf_STACKED)
        rpp_replace_1_1_NN(retval); /* pop LHS of =~ */
    else
        rpp_push_1(retval);

    if (!(rpm->op_pmflags & PMf_NONDESTRUCT)) {
        (void)SvPOK_only_UTF8(TARG);
    }

    /* See "how taint works" above */
    if (TAINTING_get) {
        if ((rxtainted & SUBST_TAINT_PAT) ||
            ((rxtainted & (SUBST_TAINT_STR|SUBST_TAINT_RETAINT)) ==
                                (SUBST_TAINT_STR|SUBST_TAINT_RETAINT))
        )
            (RXp_MATCH_TAINTED_on(prog)); /* taint $1 et al */

        if (!(rxtainted & SUBST_TAINT_BOOLRET)
            && (rxtainted & (SUBST_TAINT_STR|SUBST_TAINT_PAT))
        )
            SvTAINTED_on(retval);  /* taint return value */
        else
            SvTAINTED_off(retval);  /* may have got tainted earlier */

        /* needed for mg_set below */
        TAINT_set(
          cBOOL(rxtainted & (SUBST_TAINT_STR|SUBST_TAINT_PAT|SUBST_TAINT_REPL))
        );
        SvTAINT(TARG);
    }
    SvSETMAGIC(TARG); /* PL_tainted must be correctly set for this mg_set */
    TAINT_NOT;
    LEAVE_SCOPE(oldsave);
    return NORMAL;
}


PP(pp_grepwhile)
{
    /* Understanding the stack during a grep.
     *
     * 'grep expr, args' is implemented in the form of
     *     grepstart;
     *     do {
     *          expr;
     *          grepwhile;
     *     } while (args);
     *
     * The stack examples below are in the form of 'perl -Ds' output,
     * where any stack element indexed by PL_markstack_ptr[i] has a star
     * just to the right of it.  In addition, the corresponding i value
     * is displayed under the indexed stack element.
     *
     * On entry to grepwhile, the stack looks like this:
     *
     *      =>   *  M1..Mn  X1  *  X2..Xn  C  *  R1..Rn  BOOL
     *       [-2]          [-1]           [0]
     *
     * where:
     *   M1..Mn   Accumulated args which have been matched so far.
     *   X1..Xn   Random discardable elements from previous iterations.
     *   C        The current (just processed) arg, still aliased to $_.
     *   R1..Rn   The args remaining to be processed.
     *   BOOL     the result of the just-executed grep expression.
     *
     * Note that it is easiest to think of the top two stack marks as both
     * being one too high, and so it would make more sense to have had the
     * marks like this:
     *
     *      =>   *  M1..Mn  *  X1..Xn  *  C  R1..Rn  BOOL
     *      [-2]       [-1]        [0]
     *
     * where the stack is divided neatly into 3 groups:
     *   - matched,
     *   - discarded,
     *   - being, or yet to be, processed.
     * But off-by-one is the way it is currently, and it works as long as
     * we keep it consistent and bear it in mind.
     *
     * pp_grepwhile() does the following:
     *
     * - for a match, replace the X1 pointer with a pointer to C and bump
     *     PL_markstack_ptr[-1]
     * - if more args to process, bump PL_markstack_ptr[0] and update the
     *     $_ alias, else
     * - remove top 3 MARKs and return M1..Mn, or a scalar,
     *     or void as appropriate.
     *
     */

    bool match = SvTRUE_NN(*PL_stack_sp);
    rpp_popfree_1_NN();

    if (match) {
        SV **from_p = PL_stack_base + PL_markstack_ptr[0];
        SV **to_p   = PL_stack_base + PL_markstack_ptr[-1]++;
        SV *from    = *from_p;
        SV *to      = *to_p;

        if (from != to) {
            *to_p = from;
#ifdef PERL_RC_STACK
            SvREFCNT_inc_simple_void_NN(from);
            SvREFCNT_dec(to);
#endif
        }
    }

    ++*PL_markstack_ptr;
    FREETMPS;
    LEAVE_with_name("grep_item");					/* exit inner scope */

    /* All done yet? */
    if (UNLIKELY(PL_stack_base + *PL_markstack_ptr > PL_stack_sp)) {
        SSize_t items;
        const U8 gimme = GIMME_V;

        LEAVE_with_name("grep");					/* exit outer scope */
        (void)POPMARK;				/* pop src */
        items = --*PL_markstack_ptr - PL_markstack_ptr[-1];
        (void)POPMARK;				/* pop dst */
        SV **base = PL_stack_base + POPMARK;	/* pop original mark */

        if (gimme == G_LIST)
            rpp_popfree_to_NN(base + items);
        else {
            rpp_popfree_to_NN(base);
            if (gimme == G_SCALAR) {
                if (PL_op->op_private & OPpTRUEBOOL)
                    rpp_push_IMM(items ? &PL_sv_yes : &PL_sv_zero);
                else {
                    dTARGET;
                    TARGi(items,1);
                    rpp_push_1(TARG);
                }
            }
        }

        return NORMAL;
    }
    else {
        SV *src;

        ENTER_with_name("grep_item");					/* enter inner scope */
        SAVEVPTR(PL_curpm);

        src = PL_stack_base[TOPMARK];
        if (SvPADTMP(src)) {
            SV *newsrc = sv_mortalcopy(src);
             PL_stack_base[TOPMARK] = newsrc;
#ifdef PERL_RC_STACK
            SvREFCNT_inc_simple_void_NN(newsrc);
            SvREFCNT_dec(src);
#endif
            src = newsrc;
            PL_tmps_floor++;
        }
        SvTEMP_off(src);
        DEFSV_set(src);

        return cLOGOP->op_other;
    }
}


/* leave_adjust_stacks():
 *
 * Process a scope's return args (in the range from_sp+1 .. PL_stack_sp),
 * positioning them at to_sp+1 onwards, and do the equivalent of a
 * FREEMPS and TAINT_NOT.
 *
 * Not intended to be called in void context.
 *
 * When leaving a sub, eval, do{} or other scope, the things that need
 * doing to process the return args are:
 *    * in scalar context, only return the last arg (or PL_sv_undef if none);
 *    * for the types of return that return copies of their args (such
 *      as rvalue sub return), make a mortal copy of every return arg,
 *      except where we can optimise the copy away without it being
 *      semantically visible;
 *    * make sure that the arg isn't prematurely freed; in the case of an
 *      arg not copied, this may involve mortalising it. For example, in
 *      C<sub f { my $x = ...; $x }>, $x would be freed when we do
 *      CX_LEAVE_SCOPE(cx) unless it's protected or copied.
 *
 * What condition to use when deciding whether to pass the arg through
 * or make a copy, is determined by the 'pass' arg; its valid values are:
 *   0: rvalue sub/eval exit
 *   1: other rvalue scope exit
 *   2: :lvalue sub exit in rvalue context
 *   3: :lvalue sub exit in lvalue context and other lvalue scope exits
 *
 * There is a big issue with doing a FREETMPS. We would like to free any
 * temps created by the last statement which the sub executed, rather than
 * leaving them for the caller. In a situation where a sub call isn't
 * soon followed by a nextstate (e.g. nested recursive calls, a la
 * fibonacci()), temps can accumulate, causing memory and performance
 * issues.
 *
 * On the other hand, we don't want to free any TEMPs which are keeping
 * alive any return args that we skipped copying; nor do we wish to undo
 * any mortalising done here.
 *
 * The solution is to split the temps stack frame into two, with a cut
 * point delineating the two halves. We arrange that by the end of this
 * function, all the temps stack frame entries we wish to keep are in the
 * range  PL_tmps_floor+1.. tmps_base-1, while the ones to free now are in
 * the range  tmps_base .. PL_tmps_ix.  During the course of this
 * function, tmps_base starts off as PL_tmps_floor+1, then increases
 * whenever we find or create a temp that we know should be kept. In
 * general the stuff above tmps_base is undecided until we reach the end,
 * and we may need a sort stage for that.
 *
 * To determine whether a TEMP is keeping a return arg alive, every
 * arg that is kept rather than copied and which has the SvTEMP flag
 * set, has the flag temporarily unset, to mark it. At the end we scan
 * the temps stack frame above the cut for entries without SvTEMP and
 * keep them, while turning SvTEMP on again. Note that if we die before
 * the SvTEMPs flags are set again, its safe: at worst, subsequent use of
 * those SVs may be slightly less efficient.
 *
 * In practice various optimisations for some common cases mean we can
 * avoid most of the scanning and swapping about with the temps stack.
 */

void
Perl_leave_adjust_stacks(pTHX_ SV **from_sp, SV **to_sp, U8 gimme, int pass)
{
    SSize_t tmps_base; /* lowest index into tmps stack that needs freeing now */
    SSize_t nargs;

    PERL_ARGS_ASSERT_LEAVE_ADJUST_STACKS;

    TAINT_NOT;

    if (gimme == G_LIST) {
        nargs = PL_stack_sp - from_sp;
        from_sp++;
    }
    else {
        assert(gimme == G_SCALAR);
        if (UNLIKELY(from_sp >= PL_stack_sp)) {
            /* no return args */
            assert(from_sp == PL_stack_sp);
            rpp_xpush_IMM(&PL_sv_undef);
        }
        from_sp = PL_stack_sp;
        nargs   = 1;
    }

    /* common code for G_SCALAR and G_LIST */

#ifdef PERL_RC_STACK
    {
        /* free any items from the stack which are about to get
         * over-written */
        SV **p = from_sp - 1;
        assert(p >= to_sp);
        while (p > to_sp) {
            SV *sv = *p;
            *p-- = NULL;
            SvREFCNT_dec(sv);
        }
    }
#endif


    tmps_base = PL_tmps_floor + 1;

    assert(nargs >= 0);
    if (nargs) {
        /* pointer version of tmps_base. Not safe across temp stack
         * reallocs. */
        SV **tmps_basep;

        EXTEND_MORTAL(nargs); /* one big extend for worst-case scenario */
        tmps_basep = PL_tmps_stack + tmps_base;

        /* process each return arg */

        do {
            SV *sv = *from_sp++;

            assert(PL_tmps_ix + nargs < PL_tmps_max);
#ifdef DEBUGGING
            /* PADTMPs with container set magic shouldn't appear in the
             * wild. This assert is more important for pp_leavesublv(),
             * but by testing for it here, we're more likely to catch
             * bad cases (what with :lvalue subs not being widely
             * deployed). The two issues are that for something like
             *     sub :lvalue { $tied{foo} }
             * or
             *     sub :lvalue { substr($foo,1,2) }
             * pp_leavesublv() will croak if the sub returns a PADTMP,
             * and currently functions like pp_substr() return a mortal
             * rather than using their PADTMP when returning a PVLV.
             * This is because the PVLV will hold a ref to $foo,
             * so $foo would get delayed in being freed while
             * the PADTMP SV remained in the PAD.
             * So if this assert fails it means either:
             *  1) there is pp code similar to pp_substr that is
             *     returning a PADTMP instead of a mortal, and probably
             *     needs fixing, or
             *  2) pp_leavesublv is making unwarranted assumptions
             *     about always croaking on a PADTMP
             */
            if (SvPADTMP(sv) && SvSMAGICAL(sv)) {
                MAGIC *mg;
                for (mg = SvMAGIC(sv); mg; mg = mg->mg_moremagic) {
                    assert(PERL_MAGIC_TYPE_IS_VALUE_MAGIC(mg->mg_type));
                }
            }
#endif

            if (
               pass == 0 ? (rpp_is_lone(sv) && !SvMAGICAL(sv))
             : pass == 1 ? ((SvTEMP(sv) || SvPADTMP(sv)) && !SvMAGICAL(sv) && SvREFCNT(sv) == 1)
             : pass == 2 ? (!SvPADTMP(sv))
             : 1)
            {
                /* pass through: skip copy for logic or optimisation
                 * reasons; instead mortalise it, except that ... */

#ifdef PERL_RC_STACK
                from_sp[-1] = NULL;
#endif
                *++to_sp = sv;

                if (SvTEMP(sv)) {
                    /* ... since this SV is an SvTEMP , we don't need to
                     * re-mortalise it; instead we just need to ensure
                     * that its existing entry in the temps stack frame
                     * ends up below the cut and so avoids being freed
                     * this time round. We mark it as needing to be kept
                     * by temporarily unsetting SvTEMP; then at the end,
                     * we shuffle any !SvTEMP entries on the tmps stack
                     * back below the cut.
                     * However, there's a significant chance that there's
                     * a 1:1 correspondence between the first few (or all)
                     * elements in the return args stack frame and those
                     * in the temps stack frame; e,g.:
                     *      sub f { ....; map {...} .... },
                     * or if we're exiting multiple scopes and one of the
                     * inner scopes has already made mortal copies of each
                     * return arg.
                     *
                     * If so, this arg sv will correspond to the next item
                     * on the tmps stack above the cut, and so can be kept
                     * merely by moving the cut boundary up one, rather
                     * than messing with SvTEMP.  If all args are 1:1 then
                     * we can avoid the sorting stage below completely.
                     *
                     * If there are no items above the cut on the tmps
                     * stack, then the SvTEMP must comne from an item
                     * below the cut, so there's nothing to do.
                     */
                    if (tmps_basep <= &PL_tmps_stack[PL_tmps_ix]) {
                        if (sv == *tmps_basep)
                            tmps_basep++;
                        else
                            SvTEMP_off(sv);
                    }
                }
                else if (!SvPADTMP(sv)) {
                    /* mortalise arg to avoid it being freed during save
                     * stack unwinding. Pad tmps don't need mortalising as
                     * they're never freed. This is the equivalent of
                     * sv_2mortal(SvREFCNT_inc(sv)), except that:
                     *  * it assumes that the temps stack has already been
                     *    extended;
                     *  * it puts the new item at the cut rather than at
                     *    ++PL_tmps_ix, moving the previous occupant there
                     *    instead.
                     */
                    if (!SvIMMORTAL(sv)) {
                        SvREFCNT_inc_simple_void_NN(sv);
                        SvTEMP_on(sv);
                        /* Note that if there's nothing above the cut,
                         * this copies the garbage one slot above
                         * PL_tmps_ix onto itself. This is harmless (the
                         * stack's already been extended), but might in
                         * theory trigger warnings from tools like ASan
                         */
                        PL_tmps_stack[++PL_tmps_ix] = *tmps_basep;
                        *tmps_basep++ = sv;
                    }
                }
            }
            else {
                /* Make a mortal copy of the SV.
                 * The following code is the equivalent of sv_mortalcopy()
                 * except that:
                 *  * it assumes the temps stack has already been extended;
                 *  * it optimises the copying for some simple SV types;
                 *  * it puts the new item at the cut rather than at
                 *    ++PL_tmps_ix, moving the previous occupant there
                 *    instead.
                 */

                /* A newsv of type SVt_NULL will always be upgraded to
                 * SvTYPE(sv), where that is a SVt_PVNV or below. It is
                 * more efficient to create such types directly than
                 * upgrade to them via sv_upgrade() within sv_setsv_flags. */
                SV *newsv = (SvTYPE(sv) <= SVt_PVNV)
                            ? newSV_type(SvTYPE(sv))
                            : newSV_type(SVt_NULL);

                PL_tmps_stack[++PL_tmps_ix] = *tmps_basep;
                /* put it on the tmps stack early so it gets freed if we die */
                *tmps_basep++ = newsv;

                if (SvTYPE(sv) <= (NVSIZE <= IVSIZE ? SVt_NV : SVt_IV)) {
                    /* arg must be one of undef/IV/UV/RV - maybe NV depending on
                     * config, skip sv_setsv_flags() and do the copy directly */
                    U32 dstflags;
                    U32 srcflags = SvFLAGS(sv);

                    assert(!SvGMAGICAL(sv));
                    if (srcflags & (SVf_IOK|SVf_ROK)) {
                        SET_SVANY_FOR_BODYLESS_IV(newsv);

                        if (srcflags & SVf_ROK) {
                            newsv->sv_u.svu_rv = SvREFCNT_inc(SvRV(sv));
                            /* SV type plus flags */
                            dstflags = (SVt_IV|SVf_ROK|SVs_TEMP);
                        }
                        else {
                            /* both src and dst are <= SVt_IV, so sv_any
                             * points to the head; so access the heads
                             * directly rather than going via sv_any.
                             */
                            assert(    &(sv->sv_u.svu_iv)
                                    == &(((XPVIV*) SvANY(sv))->xiv_iv));
                            assert(    &(newsv->sv_u.svu_iv)
                                    == &(((XPVIV*) SvANY(newsv))->xiv_iv));
                            newsv->sv_u.svu_iv = sv->sv_u.svu_iv;
                            /* SV type plus flags */
                            dstflags = (SVt_IV|SVf_IOK|SVp_IOK|SVs_TEMP
                                            |(srcflags & SVf_IVisUV));
                        }
                    }
#if NVSIZE <= IVSIZE
                    else if (srcflags & SVf_NOK) {
                        SET_SVANY_FOR_BODYLESS_NV(newsv);
                        dstflags = (SVt_NV|SVf_NOK|SVp_NOK|SVs_TEMP);

                        /* both src and dst are <= SVt_MV, so sv_any points to the
                         * head; so access the head directly
                         */
                        assert(    &(sv->sv_u.svu_nv)
                                == &(((XPVNV*) SvANY(sv))->xnv_u.xnv_nv));
                        assert(    &(newsv->sv_u.svu_nv)
                                == &(((XPVNV*) SvANY(newsv))->xnv_u.xnv_nv));
                        newsv->sv_u.svu_nv = sv->sv_u.svu_nv;
                    }
#endif
                    else {
                        assert(!(srcflags & SVf_OK));
                        dstflags = (SVt_NULL|SVs_TEMP); /* SV type plus flags */
                    }
                    SvFLAGS(newsv) = dstflags;

                }
                else {
                    /* do the full sv_setsv() */
                    SSize_t old_base;

                    SvTEMP_on(newsv);
                    old_base = tmps_basep - PL_tmps_stack;
                    SvGETMAGIC(sv);
                    sv_setsv_flags(newsv, sv, SV_DO_COW_SVSETSV);
                    /* the mg_get or sv_setsv might have created new temps
                     * or realloced the tmps stack; regrow and reload */
                    EXTEND_MORTAL(nargs);
                    tmps_basep = PL_tmps_stack + old_base;
                    TAINT_NOT;	/* Each item is independent */
                }


#ifdef PERL_RC_STACK
                from_sp[-1] = NULL;
                SvREFCNT_dec_NN(sv);
                assert(!to_sp[1]);
                *++to_sp = newsv;
                SvREFCNT_inc_simple_void_NN(newsv);
#else
                *++to_sp = newsv;
#endif

            }
        } while (--nargs);

        /* If there are any temps left above the cut, we need to sort
         * them into those to keep and those to free. The only ones to
         * keep are those for which we've temporarily unset SvTEMP.
         * Work inwards from the two ends at tmps_basep .. PL_tmps_ix,
         * swapping pairs as necessary. Stop when we meet in the middle.
         */
        {
            SV **top = PL_tmps_stack + PL_tmps_ix;
            while (tmps_basep <= top) {
                SV *sv = *top;
                if (SvTEMP(sv))
                    top--;
                else {
                    SvTEMP_on(sv);
                    *top = *tmps_basep;
                    *tmps_basep = sv;
                    tmps_basep++;
                }
            }
        }

        tmps_base = tmps_basep - PL_tmps_stack;
    }

    PL_stack_sp = to_sp;

    /* unrolled FREETMPS() but using tmps_base-1 rather than PL_tmps_floor */
    while (PL_tmps_ix >= tmps_base) {
        SV* const sv = PL_tmps_stack[PL_tmps_ix--];
#ifdef PERL_POISON
        PoisonWith(PL_tmps_stack + PL_tmps_ix + 1, 1, SV *, 0xAB);
#endif
        if (LIKELY(sv)) {
            SvTEMP_off(sv);
            SvREFCNT_dec_NN(sv); /* note, can modify tmps_ix!!! */
        }
    }
}


/* also tail-called by pp_return */

PP(pp_leavesub)
{
    U8 gimme;
    PERL_CONTEXT *cx;
    SV **oldsp;
    OP *retop;

    cx = CX_CUR();
    assert(CxTYPE(cx) == CXt_SUB);

    if (CxMULTICALL(cx)) {
        /* entry zero of a stack is always PL_sv_undef, which
         * simplifies converting a '()' return into undef in scalar context */
        assert(PL_stack_sp > PL_stack_base || *PL_stack_base == &PL_sv_undef);
        return 0;
    }

    gimme = cx->blk_gimme;
    oldsp = PL_stack_base + cx->blk_oldsp; /* last arg of previous frame */

    if (gimme == G_VOID)
        rpp_popfree_to_NN(oldsp);
    else
        leave_adjust_stacks(oldsp, oldsp, gimme, 0);

    CX_LEAVE_SCOPE(cx);
    cx_popsub(cx);	/* Stack values are safe: release CV and @_ ... */
    cx_popblock(cx);
    retop = cx->blk_sub.retop;
    CX_POP(cx);

    return retop;
}


/* clear (if possible) or abandon the current @_. If 'abandon' is true,
 * forces an abandon */

void
Perl_clear_defarray(pTHX_ AV* av, bool abandon)
{
    PERL_ARGS_ASSERT_CLEAR_DEFARRAY;

    if (LIKELY(!abandon && SvREFCNT(av) == 1 && !SvMAGICAL(av))
#ifndef PERL_RC_STACK
        && !AvREAL(av)
#endif
    ) {
        clear_defarray_simple(av);
#ifndef PERL_RC_STACK
        AvREIFY_only(av);
#endif
    }
    else {
        /* abandon */
        const SSize_t size = AvFILLp(av) + 1;
        /* The ternary gives consistency with av_extend() */
        AV *newav = newAV_alloc_xz(size < PERL_ARRAY_NEW_MIN_KEY ?
                                         PERL_ARRAY_NEW_MIN_KEY : size);
#ifndef PERL_RC_STACK
        AvREIFY_only(newav);
#endif
        PAD_SVl(0) = MUTABLE_SV(newav);
        SvREFCNT_dec_NN(av);
    }
}

/* S_croak_undefined_subroutine is a helper function for pp_entersub.
 * It takes assorted DIE() logic out of that hot function.
 */
static void
S_croak_undefined_subroutine(pTHX_ CV const *cv, GV const *gv)
{
    if (cv) {
        if (CvLEXICAL(cv) && CvHASGV(cv))
            croak("Undefined subroutine &%" SVf " called",
                       SVfARG(cv_name((CV*)cv, NULL, 0)));
        else /* pp_entersub triggers when (CvANON(cv) || !CvHASGV(cv)) */
            croak("Undefined subroutine called");
    } else { /* pp_entersub triggers when (!cv) after `try_autoload` */
        SV *sub_name = newSV_type_mortal(SVt_PV);
        gv_efullname3(sub_name, gv, NULL);

        /* Heuristic to spot BOOP:boop() typo, when the intention was
         * to call BOOP::boop(). */
        const char * label = CopLABEL(PL_curcop);
        if (label && OpSIBLING(PL_curcop) == PL_op) {
            croak("Undefined subroutine &%" SVf " called, close to label '%s'",
                SVfARG(sub_name), label);
        }

        croak("Undefined subroutine &%" SVf " called", SVfARG(sub_name));
    }
    NOT_REACHED; /* NOTREACHED */
}

PP(pp_entersub)
{
    GV *gv;
    CV *cv;
    PERL_CONTEXT *cx;
    I32 old_savestack_ix;
    SV *sv = *PL_stack_sp;

    if (UNLIKELY(!sv))
        goto do_die;

    /* Locate the CV to call:
     * - most common case: RV->CV: f(), $ref->():
     *   note that if a sub is compiled before its caller is compiled,
     *   the stash entry will be a ref to a CV, rather than being a GV.
     * - second most common case: CV: $ref->method()
     */

    /* a non-magic-RV -> CV ? */
    if (LIKELY( (SvFLAGS(sv) & (SVf_ROK|SVs_GMG)) == SVf_ROK)) {
        cv = MUTABLE_CV(SvRV(sv));  /* might not actually be a CV */
        if (UNLIKELY(SvOBJECT(cv))) /* might be overloaded */
            goto do_ref;
    }
    else
        cv = MUTABLE_CV(sv);

    /* a CV ? */
    if (UNLIKELY(SvTYPE(cv) != SVt_PVCV)) {
        /* handle all the weird cases */
        switch (SvTYPE(sv)) {
        case SVt_PVLV:
            if (!isGV_with_GP(sv))
                goto do_default;
            /* FALLTHROUGH */
        case SVt_PVGV:
            cv = GvCVu((const GV *)sv);
            if (UNLIKELY(!cv)) {
                HV *stash;
                cv = sv_2cv(sv, &stash, &gv, 0);
                if (!cv) {
                    old_savestack_ix = PL_savestack_ix;
                    goto try_autoload;
                }
            }
            break;

        default:
          do_default:
            SvGETMAGIC(sv);
            if (SvROK(sv)) {
              do_ref:
                if (UNLIKELY(SvAMAGIC(sv))) {
                    sv = amagic_deref_call(sv, to_cv_amg);
                }
            }
            else {
                const char *sym;
                STRLEN len;
                if (UNLIKELY(!SvOK(sv)))
                    DIE(aTHX_ PL_no_usym, "a subroutine");

                sym = SvPV_nomg_const(sv, len);
                if (PL_op->op_private & HINT_STRICT_REFS)
                    DIE(aTHX_ "Can't use string (\"%" SVf32 "\"%s) as a subroutine ref while \"strict refs\" in use", sv, len>32 ? "..." : "");
                cv = get_cvn_flags(sym, len, GV_ADD|SvUTF8(sv));
                break;
            }
            cv = MUTABLE_CV(SvRV(sv));  /* might not actually be a CV */
            if (LIKELY(SvTYPE(cv) == SVt_PVCV))
                break;
            /* FALLTHROUGH */
        case SVt_PVHV:
        case SVt_PVAV:
          do_die:
            DIE(aTHX_ "Not a CODE reference");
        }
    }

    /* At this point we want to save PL_savestack_ix, either by doing a
     * cx_pushsub(), or for XS, doing an ENTER. But we don't yet know the final
     * CV we will be using (so we don't know whether its XS, so we can't
     * cx_pushsub() or ENTER yet), and determining cv may itself push stuff on
     * the save stack. So remember where we are currently on the save
     * stack, and later update the CX or scopestack entry accordingly. */
    old_savestack_ix = PL_savestack_ix;

    /* these two fields are in a union. If they ever become separate,
     * we have to test for both of them being null below */
    assert(cv);
    assert((void*)&CvROOT(cv) == (void*)&CvXSUB(cv));
    while (UNLIKELY(!CvROOT(cv))) {
        GV* autogv;

        /* anonymous or undef'd function leaves us no recourse */
        if (CvLEXICAL(cv) && CvHASGV(cv))
            S_croak_undefined_subroutine(aTHX_ cv, NULL);
        if (CvANON(cv) || !CvHASGV(cv))
            S_croak_undefined_subroutine(aTHX_ cv, NULL);

        /* autoloaded stub? */
        if (cv != GvCV(gv = CvGV(cv))) {
            cv = GvCV(gv);
        }
        /* should call AUTOLOAD now? */
        else {
          try_autoload:
            autogv = gv_autoload_pvn(GvSTASH(gv), GvNAME(gv), GvNAMELEN(gv),
                                     (GvNAMEUTF8(gv) ? SVf_UTF8 : 0)
                                    |(PL_op->op_flags & OPf_REF
                                       ? GV_AUTOLOAD_ISMETHOD
                                       : 0));
            cv = autogv ? GvCV(autogv) : NULL;
        }
        if (!cv)
            S_croak_undefined_subroutine(aTHX_ NULL, gv);
    }

    /* unrolled "CvCLONE(cv) && ! CvCLONED(cv)" */
    if (UNLIKELY((CvFLAGS(cv) & (CVf_CLONE|CVf_CLONED)) == CVf_CLONE))
        DIE(aTHX_ "Closure prototype called");

    if (UNLIKELY((PL_op->op_private & OPpENTERSUB_DB) && GvCV(PL_DBsub)
            && !CvNODEBUG(cv)))
    {
         Perl_get_db_sub(aTHX_ &sv, cv);
         if (CvISXSUB(cv))
             PL_curcopdb = PL_curcop;
         if (CvLVALUE(cv)) {
             /* check for lsub that handles lvalue subroutines */
             cv = GvCV(gv_fetchpvs("DB::lsub", GV_ADDMULTI, SVt_PVCV));
             /* if lsub not found then fall back to DB::sub */
             if (!cv) cv = GvCV(PL_DBsub);
         } else {
             cv = GvCV(PL_DBsub);
         }

        if (!cv || (!CvXSUB(cv) && !CvSTART(cv)))
            DIE(aTHX_ "No DB::sub routine defined");
    }

    rpp_popfree_1_NN(); /* finished with sv now */

    if (!(CvISXSUB(cv))) {
        /* This path taken at least 75% of the time   */
        dMARK;
        PADLIST *padlist;
        I32 depth;
        bool hasargs;
        U8 gimme;

        /* keep PADTMP args alive throughout the call (we need to do this
         * because @_ isn't refcounted). Note that we create the mortals
         * in the caller's tmps frame, so they won't be freed until after
         * we return from the sub.
         */
        {
            SV **svp = MARK;
            while (svp < PL_stack_sp) {
                SV *sv = *++svp;
                if (!sv)
                    continue;
                if (SvPADTMP(sv)) {
                    SV *newsv = sv_mortalcopy(sv);
                    *svp = newsv;
#ifdef PERL_RC_STACK
                    /* should just skip the mortalisation instead */
                    SvREFCNT_inc_simple_void_NN(newsv);
                    SvREFCNT_dec_NN(sv);
#endif
                    sv = newsv;
                }
                SvTEMP_off(sv);
            }
        }

        gimme = GIMME_V;
        cx = cx_pushblock(CXt_SUB, gimme, MARK, old_savestack_ix);
        hasargs = cBOOL(PL_op->op_flags & OPf_STACKED);
        cx_pushsub(cx, cv, PL_op->op_next, hasargs);

        padlist = CvPADLIST(cv);
        if (UNLIKELY((depth = ++CvDEPTH(cv)) >= 2))
            pad_push(padlist, depth);
        PAD_SET_CUR_NOSAVE(padlist, depth);
        if (LIKELY(hasargs)) {
            AV *const av = MUTABLE_AV(PAD_SVl(0));
            SSize_t items;
            AV **defavp;

            defavp = &GvAV(PL_defgv);
            cx->blk_sub.savearray = *defavp;
            *defavp = AvREFCNT_inc_simple_NN(av);

            /* it's the responsibility of whoever leaves a sub to ensure
             * that a clean, empty AV is left in pad[0]. This is normally
             * done by cx_popsub() */

#ifdef PERL_RC_STACK
            assert(AvREAL(av));
#else
            assert(!AvREAL(av));
#endif
            assert(AvFILLp(av) == -1);

            items = PL_stack_sp - MARK;
            if (UNLIKELY(items - 1 > AvMAX(av))) {
                SV **ary = AvALLOC(av);
                Renew(ary, items, SV*);
                AvMAX(av) = items - 1;
                AvALLOC(av) = ary;
                AvARRAY(av) = ary;
            }

            if (items)
                Copy(MARK+1,AvARRAY(av),items,SV*);
            AvFILLp(av) = items - 1;
#ifdef PERL_RC_STACK
            /* transfer ownership of the arguments' refcounts to av */
            PL_stack_sp = MARK;
#endif
        }
        if (UNLIKELY((cx->blk_u16 & OPpENTERSUB_LVAL_MASK) == OPpLVAL_INTRO &&
            !CvLVALUE(cv)))
            DIE(aTHX_ "Can't modify non-lvalue subroutine call of &%" SVf,
                SVfARG(cv_name(cv, NULL, 0)));
        /* warning must come *after* we fully set up the context
         * stuff so that __WARN__ handlers can safely dounwind()
         * if they want to
         */
        if (UNLIKELY(depth == PERL_SUB_DEPTH_WARN
                && ckWARN(WARN_RECURSION)
                && !(PERLDB_SUB && cv == GvCV(PL_DBsub))))
            sub_crush_depth(cv);
        return CvSTART(cv);
    }
    else {
        SSize_t markix = TOPMARK;
        bool is_scalar;

        ENTER;
        /* pretend we did the ENTER earlier */
        PL_scopestack[PL_scopestack_ix - 1] = old_savestack_ix;

        SAVETMPS;

        if (UNLIKELY(((PL_op->op_private
               & CX_PUSHSUB_GET_LVALUE_MASK(Perl_is_lvalue_sub)
             ) & OPpENTERSUB_LVAL_MASK) == OPpLVAL_INTRO &&
            !CvLVALUE(cv)))
            DIE(aTHX_ "Can't modify non-lvalue subroutine call of &%" SVf,
                SVfARG(cv_name(cv, NULL, 0)));

        if (UNLIKELY(!(PL_op->op_flags & OPf_STACKED) && GvAV(PL_defgv))) {
            /* Need to copy @_ to stack. Alternative may be to
             * switch stack to @_, and copy return values
             * back. This would allow popping @_ in XSUB, e.g.. XXXX */
            AV * const av = GvAV(PL_defgv);
            const SSize_t items = AvFILL(av) + 1;

            if (items) {
                SSize_t i = 0;
                const bool m = cBOOL(SvRMAGICAL(av));
                /* Mark is at the end of the stack. */
                rpp_extend(items);
                for (; i < items; ++i)
                {
                    SV *sv;
                    if (m) {
                        SV ** const svp = av_fetch(av, i, 0);
                        sv = svp ? *svp : NULL;
                    }
                    else
                        sv = AvARRAY(av)[i];

                    rpp_push_1(sv ? sv : av_nonelem(av, i));
                }
            }
        }
        else {
            SV **mark = PL_stack_base + markix;
            SSize_t items = PL_stack_sp - mark;
            while (items--) {
                mark++;
                if (*mark && SvPADTMP(*mark)) {
                    SV *oldsv = *mark;
                    SV *newsv = sv_mortalcopy(oldsv);
                    *mark = newsv;
#ifdef PERL_RC_STACK
                    /* should just skip the mortalisation instead */
                    SvREFCNT_inc_simple_void_NN(newsv);
                    SvREFCNT_dec_NN(oldsv);
#endif
                }
            }
        }

        /* We assume first XSUB in &DB::sub is the called one. */
        if (UNLIKELY(PL_curcopdb)) {
            SAVEVPTR(PL_curcop);
            PL_curcop = PL_curcopdb;
            PL_curcopdb = NULL;
        }
        /* Do we need to open block here? XXXX */

        /* calculate gimme here as PL_op might get changed and then not
         * restored until the LEAVE further down */
        is_scalar = (GIMME_V == G_SCALAR);

        /* CvXSUB(cv) must not be NULL because newXS() refuses NULL xsub address */
        assert(CvXSUB(cv));

        rpp_invoke_xs(cv);

#ifdef PERL_USE_HWM
        /* This duplicates the check done in runops_debug(), but provides more
         * information in the common case of the fault being with an XSUB.
         *
         * It should also catch an XSUB pushing more than it extends
         * in scalar context.
        */
        if (PL_curstackinfo->si_stack_hwm < PL_stack_sp - PL_stack_base)
            croak(
                "panic: XSUB %s::%s (%s) failed to extend arg stack: "
                "base=%p, sp=%p, hwm=%p\n",
                    HvNAME(GvSTASH(CvGV(cv))), GvNAME(CvGV(cv)), CvFILE(cv),
                    PL_stack_base, PL_stack_sp,
                    PL_stack_base + PL_curstackinfo->si_stack_hwm);
#endif
        /* Enforce some sanity in scalar context. */
        if (is_scalar) {
            SV **svp = PL_stack_base + markix + 1;
            if (svp != PL_stack_sp) {
#ifdef PERL_RC_STACK
                if (svp < PL_stack_sp) {
                    /* move return value to bottom of stack frame
                     * and free everything else */
                    SV* retsv = *PL_stack_sp;
                    *PL_stack_sp = *svp;
                    *svp = retsv;
                    rpp_popfree_to_NN(svp);
                }
                else
                    rpp_push_IMM(&PL_sv_undef);
#else
                *svp = svp > PL_stack_sp ? &PL_sv_undef : *PL_stack_sp;
                PL_stack_sp = svp;
#endif
            }
        }
        LEAVE;
        return NORMAL;
    }
}

void
Perl_sub_crush_depth(pTHX_ CV *cv)
{
    PERL_ARGS_ASSERT_SUB_CRUSH_DEPTH;

    if (CvANON(cv))
        warner(packWARN(WARN_RECURSION), "Deep recursion on anonymous subroutine");
    else {
        warner(packWARN(WARN_RECURSION), "Deep recursion on subroutine \"%" SVf "\"",
                    SVfARG(cv_name(cv,NULL,0)));
    }
}



/* like croak, but report in context of caller */

void
Perl_croak_caller(const char *pat, ...)
{
    dTHX;
    va_list args;
    const PERL_CONTEXT *cx = caller_cx(0, NULL);

    /* make error appear at call site */
    assert(cx);
    PL_curcop = cx->blk_oldcop;

    va_start(args, pat);
    vcroak(pat, &args);
    NOT_REACHED; /* NOTREACHED */
    va_end(args);
}


PP(pp_aelem)
{
    SV** svp;
    SV* const elemsv =  PL_stack_sp[0];
    IV elem = SvIV(elemsv);
    AV *const av = MUTABLE_AV(PL_stack_sp[-1]);
    const U32 lval = PL_op->op_flags & OPf_MOD || LVRET;
    const U32 defer = PL_op->op_private & OPpLVAL_DEFER;
    const bool localizing = PL_op->op_private & OPpLVAL_INTRO;
    bool preeminent = TRUE;
    SV *sv;
    SV *retsv;

    if (UNLIKELY(SvROK(elemsv) && !SvGAMAGIC(elemsv)))
        ck_warner(packWARN(WARN_MISC),
                  "Use of reference \"%" SVf "\" as array index",
                  SVfARG(elemsv));
    if (UNLIKELY(SvTYPE(av) != SVt_PVAV)) {
        retsv = &PL_sv_undef;
        goto ret;
    }

    if (UNLIKELY(localizing)) {
        /* Try to preserve the existence of a tied array
         * element by using EXISTS and DELETE if possible.
         * Fall back to FETCH and STORE otherwise. */
        if (SvCANEXISTDELETE(av))
            preeminent = av_exists(av, elem);
    }

    svp = av_fetch(av, elem, lval && !defer);
    if (lval) {
#ifdef PERL_MALLOC_WRAP
         if (SvUOK(elemsv)) {
              const UV uv = SvUV(elemsv);
              elem = uv > IV_MAX ? IV_MAX : uv;
         }
         else if (SvNOK(elemsv))
              elem = (IV)SvNV(elemsv);
         if (elem > 0) {
              MEM_WRAP_CHECK_s(elem,SV*,"Out of memory during array extend");
         }
#endif
        if (!svp || !*svp) {
            IV len;
            if (!defer)
                DIE(aTHX_ PL_no_aelem, elem);
            len = av_top_index(av);
            /* Resolve a negative index that falls within the array.  Leave
               it negative it if falls outside the array.  */
            if (elem < 0 && len + elem >= 0)
                elem = len + elem;
            if (elem >= 0 && elem <= len)
                /* Falls within the array.  */
                retsv = av_nonelem(av, elem);
            else
                /* Falls outside the array.  If it is negative,
                   magic_setdefelem will use the index for error reporting.
                 */
                retsv = sv_2mortal(newSVavdefelem(av, elem, 1));
            goto ret;
        }
        if (UNLIKELY(localizing)) {
            if (preeminent)
                save_aelem(av, elem, svp);
            else
                SAVEADELETE(av, elem);
        }
        else if (PL_op->op_private & OPpDEREF) {
            retsv = vivify_ref(*svp, PL_op->op_private & OPpDEREF);
            goto ret;
        }
    }
    sv = (svp ? *svp : &PL_sv_undef);
    if (!lval && SvRMAGICAL(av) && SvGMAGICAL(sv)) /* see note in pp_helem() */
        mg_get(sv);
    retsv = sv;

  ret:
    rpp_replace_2_1_NN(retsv);
    return NORMAL;
}

SV*
Perl_vivify_ref(pTHX_ SV *sv, U32 to_what)
{
    PERL_ARGS_ASSERT_VIVIFY_REF;

    SvGETMAGIC(sv);
    if (!SvOK(sv)) {
        if (SvREADONLY(sv))
            croak_no_modify();
        prepare_SV_for_RV(sv);
        switch (to_what) {
        case OPpDEREF_SV:
            SvRV_set(sv, newSV_type(SVt_NULL));
            break;
        case OPpDEREF_AV:
            SvRV_set(sv, MUTABLE_SV(newAV()));
            break;
        case OPpDEREF_HV:
            SvRV_set(sv, MUTABLE_SV(newHV()));
            break;
        }
        SvROK_on(sv);
        SvSETMAGIC(sv);
        SvGETMAGIC(sv);
    }
    if (SvGMAGICAL(sv)) {
        /* copy the sv without magic to prevent magic from being
           executed twice */
        SV* msv = sv_mortalcopy_flags(sv, SV_DO_COW_SVSETSV);
        return msv;
    }
    return sv;
}

PERL_STATIC_INLINE HV *
S_opmethod_stash(pTHX_ SV* meth)
{
    SV* ob;
    HV* stash;

    SV* const sv = PL_stack_base + TOPMARK == PL_stack_sp
        ? (croak("Can't call method \"%" SVf "\" without a "
                            "package or object reference", SVfARG(meth)),
           (SV *)NULL)
        : *(PL_stack_base + TOPMARK + 1);

    PERL_ARGS_ASSERT_OPMETHOD_STASH;

    if (UNLIKELY(!sv))
       undefined:
        croak("Can't call method \"%" SVf "\" on an undefined value",
                   SVfARG(meth));

    if (UNLIKELY(SvGMAGICAL(sv))) mg_get(sv);
    else if (SvIsCOW_shared_hash(sv)) { /* MyClass->meth() */
        stash = gv_stashsv(sv, GV_CACHE_ONLY);
        if (stash) return stash;
    }

    if (SvROK(sv))
        ob = MUTABLE_SV(SvRV(sv));
    else if (!SvOK(sv)) goto undefined;
    else if (isGV_with_GP(sv)) {
        if (!GvIO(sv))
            croak("Can't call method \"%" SVf "\" "
                             "without a package or object reference",
                              SVfARG(meth));
        ob = sv;
        if (SvTYPE(ob) == SVt_PVLV && LvTYPE(ob) == 'y') {
            assert(!LvTARGLEN(ob));
            ob = LvTARG(ob);
            assert(ob);
        }
        /* Replace the object at the base of the stack frame.
         * This is "below" whatever pp_wrap has wrapped, so needs freeing.
         */
        SV *newsv = sv_2mortal(newRV(ob));
        SV **svp = (PL_stack_base + TOPMARK + 1);
#ifdef PERL_RC_STACK
        SV *oldsv = *svp;
#endif
        *svp = newsv;
#ifdef PERL_RC_STACK
        SvREFCNT_inc_simple_void_NN(newsv);
        SvREFCNT_dec_NN(oldsv);
#endif
    }
    else {
        /* this isn't a reference */
        GV* iogv;
        STRLEN packlen;
        const char * const packname = SvPV_nomg_const(sv, packlen);
        const U32 packname_utf8 = SvUTF8(sv);
        stash = gv_stashpvn(packname, packlen, packname_utf8 | GV_CACHE_ONLY);
        if (stash) return stash;

        if ((PL_op->op_private & OPpMETH_NO_BAREWORD_IO) ||
            !(iogv = gv_fetchpvn_flags(
                packname, packlen, packname_utf8, SVt_PVIO
             )) ||
            !(ob=MUTABLE_SV(GvIO(iogv))))
        {
            /* this isn't the name of a filehandle either */
            if (!packlen)
            {
                croak("Can't call method \"%" SVf "\" "
                                 "without a package or object reference",
                                  SVfARG(meth));
            }
            /* assume it's a package name */
            stash = gv_stashpvn(packname, packlen, packname_utf8);
            if (stash) return stash;
            else return MUTABLE_HV(sv);
        }
        /* it _is_ a filehandle name -- replace with a reference.
         * Replace the object at the base of the stack frame.
         * This is "below" whatever pp_wrap has wrapped, so needs freeing.
         */
        SV *newsv = sv_2mortal(newRV(MUTABLE_SV(iogv)));
        SV **svp = (PL_stack_base + TOPMARK + 1);
#ifdef PERL_RC_STACK
        SV *oldsv = *svp;
#endif
        *svp = newsv;
#ifdef PERL_RC_STACK
        SvREFCNT_inc_simple_void_NN(newsv);
        SvREFCNT_dec_NN(oldsv);
#endif
    }

    /* if we got here, ob should be an object or a glob */
    if (!ob || !(SvOBJECT(ob)
                 || (isGV_with_GP(ob)
                     && (ob = MUTABLE_SV(GvIO((const GV *)ob)))
                     && SvOBJECT(ob))))
    {
        croak("Can't call method \"%" SVf "\" on unblessed reference",
                   SVfARG((SvPOK(meth) && SvPVX(meth) == PL_isa_DOES)
                                        ? newSVpvs_flags("DOES", SVs_TEMP)
                                        : meth));
    }

    return SvSTASH(ob);
}

PP(pp_method)
{
    GV* gv;
    HV* stash;
    SV* const meth = *PL_stack_sp;

    if (SvROK(meth)) {
        SV* const rmeth = SvRV(meth);
        if (SvTYPE(rmeth) == SVt_PVCV) {
            rpp_replace_1_1_NN(rmeth);
            return NORMAL;
        }
    }

    stash = opmethod_stash(meth);

    gv = gv_fetchmethod_sv_flags(stash, meth, GV_AUTOLOAD|GV_CROAK);
    assert(gv);

    rpp_replace_1_1_NN(isGV(gv) ? MUTABLE_SV(GvCV(gv)) : MUTABLE_SV(gv));
    return NORMAL;
}

#define METHOD_CHECK_CACHE(stash,cache,meth) 				\
    const HE* const he = hv_fetch_ent(cache, meth, 0, 0);		\
    if (he) {								\
        gv = MUTABLE_GV(HeVAL(he));					\
        if (isGV(gv) && GvCV(gv) && (!GvCVGEN(gv) || GvCVGEN(gv)	\
             == (PL_sub_generation + HvMROMETA(stash)->cache_gen)))	\
        {								\
            rpp_xpush_1(MUTABLE_SV(GvCV(gv)));				\
            return NORMAL;						\
        }								\
    }									\

PP(pp_method_named)
{
    GV* gv;
    SV* const meth = cMETHOP_meth;
    HV* const stash = opmethod_stash(meth);

    if (LIKELY(SvTYPE(stash) == SVt_PVHV)) {
        METHOD_CHECK_CACHE(stash, stash, meth);
    }

    gv = gv_fetchmethod_sv_flags(stash, meth, GV_AUTOLOAD|GV_CROAK);
    assert(gv);

    rpp_xpush_1(isGV(gv) ? MUTABLE_SV(GvCV(gv)) : MUTABLE_SV(gv));
    return NORMAL;
}

PP(pp_method_super)
{
    GV* gv;
    HV* cache;
    SV* const meth = cMETHOP_meth;
    HV* const stash = CopSTASH(PL_curcop);
    /* Actually, SUPER doesn't need real object's (or class') stash at all,
     * as it uses CopSTASH. However, we must ensure that object(class) is
     * correct (this check is done by S_opmethod_stash) */
    opmethod_stash(meth);

    if ((cache = HvMROMETA(stash)->super)) {
        METHOD_CHECK_CACHE(stash, cache, meth);
    }

    gv = gv_fetchmethod_sv_flags(stash, meth, GV_AUTOLOAD|GV_CROAK|GV_SUPER);
    assert(gv);

    rpp_xpush_1(isGV(gv) ? MUTABLE_SV(GvCV(gv)) : MUTABLE_SV(gv));
    return NORMAL;
}

PP(pp_method_redir)
{
    GV* gv;
    SV* const meth = cMETHOP_meth;
    HV* stash = gv_stashsv(cMETHOP_rclass, 0);
    opmethod_stash(meth); /* not used but needed for error checks */

    if (stash) { METHOD_CHECK_CACHE(stash, stash, meth); }
    else stash = MUTABLE_HV(cMETHOP_rclass);

    gv = gv_fetchmethod_sv_flags(stash, meth, GV_AUTOLOAD|GV_CROAK);
    assert(gv);

    rpp_xpush_1(isGV(gv) ? MUTABLE_SV(GvCV(gv)) : MUTABLE_SV(gv));
    return NORMAL;
}

PP(pp_method_redir_super)
{
    GV* gv;
    HV* cache;
    SV* const meth = cMETHOP_meth;
    HV* stash = gv_stashsv(cMETHOP_rclass, 0);
    opmethod_stash(meth); /* not used but needed for error checks */

    if (UNLIKELY(!stash)) stash = MUTABLE_HV(cMETHOP_rclass);
    else if ((cache = HvMROMETA(stash)->super)) {
         METHOD_CHECK_CACHE(stash, cache, meth);
    }

    gv = gv_fetchmethod_sv_flags(stash, meth, GV_AUTOLOAD|GV_CROAK|GV_SUPER);
    assert(gv);

    rpp_xpush_1(isGV(gv) ? MUTABLE_SV(GvCV(gv)) : MUTABLE_SV(gv));
    return NORMAL;
}

/*
 * ex: set ts=8 sts=4 sw=4 et:
 */