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Auto merge of #121662 - saethlin:precondition-unification, r=RalfJung
Distinguish between library and lang UB in assert_unsafe_precondition As described in #121583 (comment), `assert_unsafe_precondition` now explicitly distinguishes between language UB (conditions we explicitly optimize on) and library UB (things we document you shouldn't do, and maybe some library internals assume you don't do). `debug_assert_nounwind` was originally added to avoid the "only at runtime" aspect of `assert_unsafe_precondition`. Since then the difference between the macros has gotten muddied. This totally revamps the situation. Now _all_ preconditions shall be checked with `assert_unsafe_precondition`. If you have a precondition that's only checkable at runtime, do a `const_eval_select` hack, as done in this PR. r? RalfJung
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‎compiler/rustc_borrowck/src/type_check/mod.rs

Lines changed: 1 addition & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -2000,7 +2000,7 @@ impl<'a, 'tcx> TypeChecker<'a, 'tcx> {
20002000
ConstraintCategory::SizedBound,
20012001
);
20022002
}
2003-
&Rvalue::NullaryOp(NullOp::DebugAssertions, _) => {}
2003+
&Rvalue::NullaryOp(NullOp::UbCheck(_), _) => {}
20042004

20052005
Rvalue::ShallowInitBox(operand, ty) => {
20062006
self.check_operand(operand, location);

‎compiler/rustc_codegen_cranelift/src/base.rs

Lines changed: 1 addition & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -779,7 +779,7 @@ fn codegen_stmt<'tcx>(
779779
NullOp::OffsetOf(fields) => {
780780
layout.offset_of_subfield(fx, fields.iter()).bytes()
781781
}
782-
NullOp::DebugAssertions => {
782+
NullOp::UbCheck(_) => {
783783
let val = fx.tcx.sess.opts.debug_assertions;
784784
let val = CValue::by_val(
785785
fx.bcx.ins().iconst(types::I8, i64::try_from(val).unwrap()),

‎compiler/rustc_codegen_ssa/src/mir/rvalue.rs

Lines changed: 2 additions & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -685,7 +685,8 @@ impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
685685
let val = layout.offset_of_subfield(bx.cx(), fields.iter()).bytes();
686686
bx.cx().const_usize(val)
687687
}
688-
mir::NullOp::DebugAssertions => {
688+
mir::NullOp::UbCheck(_) => {
689+
// In codegen, we want to check for language UB and library UB
689690
let val = bx.tcx().sess.opts.debug_assertions;
690691
bx.cx().const_bool(val)
691692
}

‎compiler/rustc_const_eval/src/interpret/step.rs

Lines changed: 10 additions & 4 deletions
Original file line numberDiff line numberDiff line change
@@ -258,10 +258,16 @@ impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
258258
let val = layout.offset_of_subfield(self, fields.iter()).bytes();
259259
Scalar::from_target_usize(val, self)
260260
}
261-
mir::NullOp::DebugAssertions => {
262-
// The checks hidden behind this are always better done by the interpreter
263-
// itself, because it knows the runtime state better.
264-
Scalar::from_bool(false)
261+
mir::NullOp::UbCheck(kind) => {
262+
// We want to enable checks for library UB, because the interpreter doesn't
263+
// know about those on its own.
264+
// But we want to disable checks for language UB, because the interpreter
265+
// has its own better checks for that.
266+
let should_check = match kind {
267+
mir::UbKind::LibraryUb => self.tcx.sess.opts.debug_assertions,
268+
mir::UbKind::LanguageUb => false,
269+
};
270+
Scalar::from_bool(should_check)
265271
}
266272
};
267273
self.write_scalar(val, &dest)?;

‎compiler/rustc_const_eval/src/transform/check_consts/check.rs

Lines changed: 1 addition & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -558,7 +558,7 @@ impl<'tcx> Visitor<'tcx> for Checker<'_, 'tcx> {
558558
Rvalue::Cast(_, _, _) => {}
559559

560560
Rvalue::NullaryOp(
561-
NullOp::SizeOf | NullOp::AlignOf | NullOp::OffsetOf(_) | NullOp::DebugAssertions,
561+
NullOp::SizeOf | NullOp::AlignOf | NullOp::OffsetOf(_) | NullOp::UbCheck(_),
562562
_,
563563
) => {}
564564
Rvalue::ShallowInitBox(_, _) => {}

‎compiler/rustc_const_eval/src/transform/validate.rs

Lines changed: 1 addition & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -1157,7 +1157,7 @@ impl<'a, 'tcx> Visitor<'tcx> for TypeChecker<'a, 'tcx> {
11571157
Rvalue::Repeat(_, _)
11581158
| Rvalue::ThreadLocalRef(_)
11591159
| Rvalue::AddressOf(_, _)
1160-
| Rvalue::NullaryOp(NullOp::SizeOf | NullOp::AlignOf | NullOp::DebugAssertions, _)
1160+
| Rvalue::NullaryOp(NullOp::SizeOf | NullOp::AlignOf | NullOp::UbCheck(_), _)
11611161
| Rvalue::Discriminant(_) => {}
11621162
}
11631163
self.super_rvalue(rvalue, location);

‎compiler/rustc_hir_analysis/src/check/intrinsic.rs

Lines changed: 3 additions & 2 deletions
Original file line numberDiff line numberDiff line change
@@ -127,7 +127,8 @@ pub fn intrinsic_operation_unsafety(tcx: TyCtxt<'_>, intrinsic_id: LocalDefId) -
127127
| sym::variant_count
128128
| sym::is_val_statically_known
129129
| sym::ptr_mask
130-
| sym::debug_assertions
130+
| sym::check_language_ub
131+
| sym::check_library_ub
131132
| sym::fadd_algebraic
132133
| sym::fsub_algebraic
133134
| sym::fmul_algebraic
@@ -584,7 +585,7 @@ pub fn check_intrinsic_type(
584585
(0, 0, vec![Ty::new_imm_ptr(tcx, Ty::new_unit(tcx))], tcx.types.usize)
585586
}
586587

587-
sym::debug_assertions => (0, 1, Vec::new(), tcx.types.bool),
588+
sym::check_language_ub | sym::check_library_ub => (0, 1, Vec::new(), tcx.types.bool),
588589

589590
sym::simd_eq
590591
| sym::simd_ne

‎compiler/rustc_middle/src/mir/pretty.rs

Lines changed: 1 addition & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -915,7 +915,7 @@ impl<'tcx> Debug for Rvalue<'tcx> {
915915
NullOp::SizeOf => write!(fmt, "SizeOf({t})"),
916916
NullOp::AlignOf => write!(fmt, "AlignOf({t})"),
917917
NullOp::OffsetOf(fields) => write!(fmt, "OffsetOf({t}, {fields:?})"),
918-
NullOp::DebugAssertions => write!(fmt, "cfg!(debug_assertions)"),
918+
NullOp::UbCheck(kind) => write!(fmt, "UbCheck({kind:?})"),
919919
}
920920
}
921921
ThreadLocalRef(did) => ty::tls::with(|tcx| {

‎compiler/rustc_middle/src/mir/syntax.rs

Lines changed: 10 additions & 2 deletions
Original file line numberDiff line numberDiff line change
@@ -1366,8 +1366,16 @@ pub enum NullOp<'tcx> {
13661366
AlignOf,
13671367
/// Returns the offset of a field
13681368
OffsetOf(&'tcx List<(VariantIdx, FieldIdx)>),
1369-
/// cfg!(debug_assertions), but expanded in codegen
1370-
DebugAssertions,
1369+
/// Returns whether we want to check for library UB or language UB at monomorphization time.
1370+
/// Both kinds of UB evaluate to `true` in codegen, and only library UB evalutes to `true` in
1371+
/// const-eval/Miri, because the interpreter has its own better checks for language UB.
1372+
UbCheck(UbKind),
1373+
}
1374+
1375+
#[derive(Clone, Copy, Debug, PartialEq, Eq, TyEncodable, TyDecodable, Hash, HashStable)]
1376+
pub enum UbKind {
1377+
LanguageUb,
1378+
LibraryUb,
13711379
}
13721380

13731381
#[derive(Copy, Clone, Debug, PartialEq, Eq, PartialOrd, Ord, Hash)]

‎compiler/rustc_middle/src/mir/tcx.rs

Lines changed: 1 addition & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -194,7 +194,7 @@ impl<'tcx> Rvalue<'tcx> {
194194
Rvalue::NullaryOp(NullOp::SizeOf | NullOp::AlignOf | NullOp::OffsetOf(..), _) => {
195195
tcx.types.usize
196196
}
197-
Rvalue::NullaryOp(NullOp::DebugAssertions, _) => tcx.types.bool,
197+
Rvalue::NullaryOp(NullOp::UbCheck(_), _) => tcx.types.bool,
198198
Rvalue::Aggregate(ref ak, ref ops) => match **ak {
199199
AggregateKind::Array(ty) => Ty::new_array(tcx, ty, ops.len() as u64),
200200
AggregateKind::Tuple => {

‎compiler/rustc_mir_dataflow/src/move_paths/builder.rs

Lines changed: 1 addition & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -433,7 +433,7 @@ impl<'b, 'a, 'tcx, F: Fn(Ty<'tcx>) -> bool> Gatherer<'b, 'a, 'tcx, F> {
433433
| Rvalue::Discriminant(..)
434434
| Rvalue::Len(..)
435435
| Rvalue::NullaryOp(
436-
NullOp::SizeOf | NullOp::AlignOf | NullOp::OffsetOf(..) | NullOp::DebugAssertions,
436+
NullOp::SizeOf | NullOp::AlignOf | NullOp::OffsetOf(..) | NullOp::UbCheck(_),
437437
_,
438438
) => {}
439439
}

‎compiler/rustc_mir_transform/src/gvn.rs

Lines changed: 1 addition & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -488,7 +488,7 @@ impl<'body, 'tcx> VnState<'body, 'tcx> {
488488
NullOp::OffsetOf(fields) => {
489489
layout.offset_of_subfield(&self.ecx, fields.iter()).bytes()
490490
}
491-
NullOp::DebugAssertions => return None,
491+
NullOp::UbCheck(_) => return None,
492492
};
493493
let usize_layout = self.ecx.layout_of(self.tcx.types.usize).unwrap();
494494
let imm = ImmTy::try_from_uint(val, usize_layout)?;

‎compiler/rustc_mir_transform/src/known_panics_lint.rs

Lines changed: 1 addition & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -639,7 +639,7 @@ impl<'mir, 'tcx> ConstPropagator<'mir, 'tcx> {
639639
NullOp::OffsetOf(fields) => {
640640
op_layout.offset_of_subfield(self, fields.iter()).bytes()
641641
}
642-
NullOp::DebugAssertions => return None,
642+
NullOp::UbCheck(_) => return None,
643643
};
644644
ImmTy::from_scalar(Scalar::from_target_usize(val, self), layout).into()
645645
}

‎compiler/rustc_mir_transform/src/lower_intrinsics.rs

Lines changed: 19 additions & 2 deletions
Original file line numberDiff line numberDiff line change
@@ -20,13 +20,30 @@ impl<'tcx> MirPass<'tcx> for LowerIntrinsics {
2020
sym::unreachable => {
2121
terminator.kind = TerminatorKind::Unreachable;
2222
}
23-
sym::debug_assertions => {
23+
sym::check_language_ub => {
2424
let target = target.unwrap();
2525
block.statements.push(Statement {
2626
source_info: terminator.source_info,
2727
kind: StatementKind::Assign(Box::new((
2828
*destination,
29-
Rvalue::NullaryOp(NullOp::DebugAssertions, tcx.types.bool),
29+
Rvalue::NullaryOp(
30+
NullOp::UbCheck(UbKind::LanguageUb),
31+
tcx.types.bool,
32+
),
33+
))),
34+
});
35+
terminator.kind = TerminatorKind::Goto { target };
36+
}
37+
sym::check_library_ub => {
38+
let target = target.unwrap();
39+
block.statements.push(Statement {
40+
source_info: terminator.source_info,
41+
kind: StatementKind::Assign(Box::new((
42+
*destination,
43+
Rvalue::NullaryOp(
44+
NullOp::UbCheck(UbKind::LibraryUb),
45+
tcx.types.bool,
46+
),
3047
))),
3148
});
3249
terminator.kind = TerminatorKind::Goto { target };

‎compiler/rustc_mir_transform/src/promote_consts.rs

Lines changed: 1 addition & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -446,7 +446,7 @@ impl<'tcx> Validator<'_, 'tcx> {
446446
NullOp::SizeOf => {}
447447
NullOp::AlignOf => {}
448448
NullOp::OffsetOf(_) => {}
449-
NullOp::DebugAssertions => {}
449+
NullOp::UbCheck(_) => {}
450450
},
451451

452452
Rvalue::ShallowInitBox(_, _) => return Err(Unpromotable),

‎compiler/rustc_smir/src/rustc_smir/convert/mir.rs

Lines changed: 7 additions & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -251,13 +251,19 @@ impl<'tcx> Stable<'tcx> for mir::NullOp<'tcx> {
251251
type T = stable_mir::mir::NullOp;
252252
fn stable(&self, tables: &mut Tables<'_>) -> Self::T {
253253
use rustc_middle::mir::NullOp::*;
254+
use rustc_middle::mir::UbKind;
254255
match self {
255256
SizeOf => stable_mir::mir::NullOp::SizeOf,
256257
AlignOf => stable_mir::mir::NullOp::AlignOf,
257258
OffsetOf(indices) => stable_mir::mir::NullOp::OffsetOf(
258259
indices.iter().map(|idx| idx.stable(tables)).collect(),
259260
),
260-
DebugAssertions => stable_mir::mir::NullOp::DebugAssertions,
261+
UbCheck(UbKind::LanguageUb) => {
262+
stable_mir::mir::NullOp::UbCheck(stable_mir::mir::UbKind::LanguageUb)
263+
}
264+
UbCheck(UbKind::LibraryUb) => {
265+
stable_mir::mir::NullOp::UbCheck(stable_mir::mir::UbKind::LibraryUb)
266+
}
261267
}
262268
}
263269
}

‎compiler/rustc_span/src/symbol.rs

Lines changed: 2 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -518,6 +518,8 @@ symbols! {
518518
cfi,
519519
cfi_encoding,
520520
char,
521+
check_language_ub,
522+
check_library_ub,
521523
client,
522524
clippy,
523525
clobber_abi,

‎compiler/stable_mir/src/mir/body.rs

Lines changed: 8 additions & 2 deletions
Original file line numberDiff line numberDiff line change
@@ -639,7 +639,7 @@ impl Rvalue {
639639
Rvalue::NullaryOp(NullOp::SizeOf | NullOp::AlignOf | NullOp::OffsetOf(..), _) => {
640640
Ok(Ty::usize_ty())
641641
}
642-
Rvalue::NullaryOp(NullOp::DebugAssertions, _) => Ok(Ty::bool_ty()),
642+
Rvalue::NullaryOp(NullOp::UbCheck(_), _) => Ok(Ty::bool_ty()),
643643
Rvalue::Aggregate(ak, ops) => match *ak {
644644
AggregateKind::Array(ty) => Ty::try_new_array(ty, ops.len() as u64),
645645
AggregateKind::Tuple => Ok(Ty::new_tuple(
@@ -1007,7 +1007,13 @@ pub enum NullOp {
10071007
/// Returns the offset of a field.
10081008
OffsetOf(Vec<(VariantIdx, FieldIdx)>),
10091009
/// cfg!(debug_assertions), but at codegen time
1010-
DebugAssertions,
1010+
UbCheck(UbKind),
1011+
}
1012+
1013+
#[derive(Clone, Debug, Eq, PartialEq)]
1014+
pub enum UbKind {
1015+
LanguageUb,
1016+
LibraryUb,
10111017
}
10121018

10131019
impl Operand {

‎library/core/src/cell.rs

Lines changed: 6 additions & 2 deletions
Original file line numberDiff line numberDiff line change
@@ -237,7 +237,6 @@
237237

238238
use crate::cmp::Ordering;
239239
use crate::fmt::{self, Debug, Display};
240-
use crate::intrinsics;
241240
use crate::marker::{PhantomData, Unsize};
242241
use crate::mem::{self, size_of};
243242
use crate::ops::{CoerceUnsized, Deref, DerefMut, DispatchFromDyn};
@@ -435,8 +434,13 @@ impl<T> Cell<T> {
435434
#[inline]
436435
#[stable(feature = "move_cell", since = "1.17.0")]
437436
pub fn swap(&self, other: &Self) {
437+
// This function documents that it *will* panic, and intrinsics::is_nonoverlapping doesn't
438+
// do the check in const, so trying to use it here would be inviting unnecessary fragility.
438439
fn is_nonoverlapping<T>(src: *const T, dst: *const T) -> bool {
439-
intrinsics::is_nonoverlapping(src.cast(), dst.cast(), size_of::<T>(), 1)
440+
let src_usize = src.addr();
441+
let dst_usize = dst.addr();
442+
let diff = src_usize.abs_diff(dst_usize);
443+
diff >= size_of::<T>()
440444
}
441445

442446
if ptr::eq(self, other) {

‎library/core/src/char/convert.rs

Lines changed: 1 addition & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -26,6 +26,7 @@ pub(super) const unsafe fn from_u32_unchecked(i: u32) -> char {
2626
// SAFETY: the caller must guarantee that `i` is a valid char value.
2727
unsafe {
2828
assert_unsafe_precondition!(
29+
check_language_ub,
2930
"invalid value for `char`",
3031
(i: u32 = i) => char_try_from_u32(i).is_ok()
3132
);

‎library/core/src/hint.rs

Lines changed: 7 additions & 4 deletions
Original file line numberDiff line numberDiff line change
@@ -98,12 +98,14 @@ use crate::intrinsics;
9898
#[rustc_const_stable(feature = "const_unreachable_unchecked", since = "1.57.0")]
9999
#[cfg_attr(miri, track_caller)] // even without panics, this helps for Miri backtraces
100100
pub const unsafe fn unreachable_unchecked() -> ! {
101+
intrinsics::assert_unsafe_precondition!(
102+
check_language_ub,
103+
"hint::unreachable_unchecked must never be reached",
104+
() => false
105+
);
101106
// SAFETY: the safety contract for `intrinsics::unreachable` must
102107
// be upheld by the caller.
103-
unsafe {
104-
intrinsics::assert_unsafe_precondition!("hint::unreachable_unchecked must never be reached", () => false);
105-
intrinsics::unreachable()
106-
}
108+
unsafe { intrinsics::unreachable() }
107109
}
108110

109111
/// Makes a *soundness* promise to the compiler that `cond` holds.
@@ -147,6 +149,7 @@ pub const unsafe fn assert_unchecked(cond: bool) {
147149
// SAFETY: The caller promised `cond` is true.
148150
unsafe {
149151
intrinsics::assert_unsafe_precondition!(
152+
check_language_ub,
150153
"hint::assert_unchecked must never be called when the condition is false",
151154
(cond: bool = cond) => cond,
152155
);

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