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Auto merge of #94512 - RalfJung:sdiv-ub, r=oli-obk

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Miri/CTFE: properly treat overflow in (signed) division/rem as UB

To my surprise, it looks like LLVM treats overflow of signed div/rem as UB. From what I can tell, MIR `Div`/`Rem` directly lowers to the corresponding LLVM operation, so to make that correct we also have to consider these overflows UB in the CTFE/Miri interpreter engine.

r? `@oli-obk`
This commit is contained in:
bors 2022-03-03 12:56:24 +00:00
commit 4566094913
11 changed files with 97 additions and 80 deletions
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11
compiler/rustc_mir_transform/src/const_prop.rs
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@ -1196,12 +1196,21 @@ impl<'tcx> MutVisitor<'tcx> for ConstPropagator<'_, 'tcx> {
AssertKind::RemainderByZero(op) => {
Some(AssertKind::RemainderByZero(eval_to_int(op)))
}
AssertKind::Overflow(bin_op @ (BinOp::Div | BinOp::Rem), op1, op2) => {
// Division overflow is *UB* in the MIR, and different than the
// other overflow checks.
Some(AssertKind::Overflow(
*bin_op,
eval_to_int(op1),
eval_to_int(op2),
))
}
AssertKind::BoundsCheck { ref len, ref index } => {
let len = eval_to_int(len);
let index = eval_to_int(index);
Some(AssertKind::BoundsCheck { len, index })
}
// Overflow is are already covered by checks on the binary operators.
// Remaining overflow errors are already covered by checks on the binary operators.
AssertKind::Overflow(..) | AssertKind::OverflowNeg(_) => None,
// Need proper const propagator for these.
_ => None,