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DestinationPropagation: avoid creating overlapping assignments. #146516

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Merged
merged 4 commits into from
Sep 16, 2025
Merged

DestinationPropagation: avoid creating overlapping assignments. #146516

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d51aec7
Add test.
cjgillot Sep 13, 2025
aee7d70
Mark reads in statements to avoid overlapping assingments.
cjgillot Sep 13, 2025
8811344
Elaborate comment.
cjgillot Sep 14, 2025
d58061e
Restrict simple assignment condition.
cjgillot Sep 16, 2025
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Restrict simple assignment condition.
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@cjgillot
cjgillot committed Sep 16, 2025
commit d58061e6131f6141985faadb6794af540f81b1db
10 changes: 8 additions & 2 deletions compiler/rustc_mir_transform/src/dest_prop.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -596,8 +596,14 @@ fn save_as_intervals<'tcx>(
// 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(_))));
let is_simple_assignment = match stmt.kind {
StatementKind::Assign(box (
lhs,
Rvalue::CopyForDeref(rhs)
| Rvalue::Use(Operand::Copy(rhs) | Operand::Move(rhs)),
)) => lhs.projection == rhs.projection,
_ => false,
};
VisitPlacesWith(|place: Place<'tcx>, ctxt| {
if let Some(relevant) = relevant.shrink[place.local] {
match DefUse::for_place(place, ctxt) {
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