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Elaborate comment.

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This commit is contained in:
Camille Gillot 2025-09-14 13:04:53 +00:00
parent aee7d703c5
commit 8811344f22
1 changed files with 6 additions and 2 deletions
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8
compiler/rustc_mir_transform/src/dest_prop.rs
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@ -590,8 +590,12 @@ fn save_as_intervals<'tcx>(
twostep = TwoStepIndex::from_u32(twostep.as_u32() + 1);
debug_assert_eq!(twostep, two_step_loc(loc, Effect::After));
append_at(&mut values, &state, twostep);
// Ensure we have a non-zero live range even for dead stores. This is done by marking
// all the written-to locals as live in the second half of the statement.
// Like terminators, ensure we have a non-zero live range even for dead stores.
// Some rvalues interleave reads and writes, for instance `Rvalue::Aggregate`, see
// https://github.com/rust-lang/rust/issues/146383. By precaution, treat statements
// as behaving so by default.
// We make an exception for simple assignments `_a.stuff = {copy|move} _b.stuff`,
// as marking `_b` live here would prevent unification.
let is_simple_assignment =
matches!(stmt.kind, StatementKind::Assign(box (_, Rvalue::Use(_))));
VisitPlacesWith(|place: Place<'tcx>, ctxt| {