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Auto merge of #121662 - saethlin:precondition-unification, r=RalfJung

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Distinguish between library and lang UB in assert_unsafe_precondition

As described in https://github.com/rust-lang/rust/pull/121583#issuecomment-1963168186, `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
This commit is contained in:
bors 2024-03-10 01:23:54 +00:00
commit 768408af12
47 changed files with 419 additions and 263 deletions
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2
compiler/rustc_middle/src/mir/pretty.rs
View file

@ -915,7 +915,7 @@ impl<'tcx> Debug for Rvalue<'tcx> {
NullOp::SizeOf => write!(fmt, "SizeOf({t})"),
NullOp::AlignOf => write!(fmt, "AlignOf({t})"),
NullOp::OffsetOf(fields) => write!(fmt, "OffsetOf({t}, {fields:?})"),
NullOp::DebugAssertions => write!(fmt, "cfg!(debug_assertions)"),
NullOp::UbCheck(kind) => write!(fmt, "UbCheck({kind:?})"),
}
}
ThreadLocalRef(did) => ty::tls::with(|tcx| {

12
compiler/rustc_middle/src/mir/syntax.rs
View file

@ -1366,8 +1366,16 @@ pub enum NullOp<'tcx> {
AlignOf,
/// Returns the offset of a field
OffsetOf(&'tcx List<(VariantIdx, FieldIdx)>),
/// cfg!(debug_assertions), but expanded in codegen
DebugAssertions,
/// Returns whether we want to check for library UB or language UB at monomorphization time.
/// Both kinds of UB evaluate to `true` in codegen, and only library UB evalutes to `true` in
/// const-eval/Miri, because the interpreter has its own better checks for language UB.
UbCheck(UbKind),
}
#[derive(Clone, Copy, Debug, PartialEq, Eq, TyEncodable, TyDecodable, Hash, HashStable)]
pub enum UbKind {
LanguageUb,
LibraryUb,
}
#[derive(Copy, Clone, Debug, PartialEq, Eq, PartialOrd, Ord, Hash)]

2
compiler/rustc_middle/src/mir/tcx.rs
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@ -194,7 +194,7 @@ impl<'tcx> Rvalue<'tcx> {
Rvalue::NullaryOp(NullOp::SizeOf | NullOp::AlignOf | NullOp::OffsetOf(..), _) => {
tcx.types.usize
}
Rvalue::NullaryOp(NullOp::DebugAssertions, _) => tcx.types.bool,
Rvalue::NullaryOp(NullOp::UbCheck(_), _) => tcx.types.bool,
Rvalue::Aggregate(ref ak, ref ops) => match **ak {
AggregateKind::Array(ty) => Ty::new_array(tcx, ty, ops.len() as u64),
AggregateKind::Tuple => {