op_dump: display a PMOP's regex address/offset

When doing a low-level dump of a pattern-match op (PMOP), it currently
displays a stringified representation of the regex attached to the op.
This commit makes it also display the regex SV's address and, on
threaded builds, the offset within the regex pad where that SV is
stored.

Author: iabyn

dump.c

@@ -979,6 +979,13 @@ S_do_pmop_dump_bar(pTHX_ I32 level, UV bar, PerlIO *file, const PMOP *pm)
 
     kidbar = ((bar << 1) | cBOOL(pm->op_flags & OPf_KIDS)) << 1;
 
+#ifdef USE_ITHREADS
+    S_opdump_indent(aTHX_ (OP*)pm, level, bar, file,
+                    "PMOFFSET = %" IVdf "\n", (IV)pm->op_pmoffset);
+#endif
+    S_opdump_indent(aTHX_ (OP*)pm, level, bar, file,
+                    "REGEX = 0x%" UVxf "\n", PTR2UV(PM_GETRE(pm)));
+
     if (PM_GETRE(pm)) {
         char ch = (pm->op_pmflags & PMf_ONCE) ? '?' : '/';
         S_opdump_indent(aTHX_ (OP*)pm, level, bar, file, "PMf_PRE %c%.*s%c\n",