From aee7d703c58b68611785684bbb8e402c1471992b Mon Sep 17 00:00:00 2001 From: Camille Gillot Date: Sat, 13 Sep 2025 18:07:22 +0000 Subject: Mark reads in statements to avoid overlapping assingments. --- compiler/rustc_mir_transform/src/dest_prop.rs | 29 ++++++++++++++++++--------- 1 file changed, 19 insertions(+), 10 deletions(-) (limited to 'compiler') diff --git a/compiler/rustc_mir_transform/src/dest_prop.rs b/compiler/rustc_mir_transform/src/dest_prop.rs index 9ba2d274691..7e6f39881b8 100644 --- a/compiler/rustc_mir_transform/src/dest_prop.rs +++ b/compiler/rustc_mir_transform/src/dest_prop.rs @@ -567,13 +567,15 @@ fn save_as_intervals<'tcx>( // the written-to locals as live in the second half of the statement. // We also ensure that operands read by terminators conflict with writes by that terminator. // For instance a function call may read args after having written to the destination. - VisitPlacesWith(|place, ctxt| match DefUse::for_place(place, ctxt) { - DefUse::Def | DefUse::Use | DefUse::PartialWrite => { - if let Some(relevant) = relevant.shrink[place.local] { - values.insert(relevant, twostep); + VisitPlacesWith(|place: Place<'tcx>, ctxt| { + if let Some(relevant) = relevant.shrink[place.local] { + match DefUse::for_place(place, ctxt) { + DefUse::Def | DefUse::Use | DefUse::PartialWrite => { + values.insert(relevant, twostep); + } + DefUse::NonUse => {} } } - DefUse::NonUse => {} }) .visit_terminator(term, loc); @@ -590,13 +592,20 @@ fn save_as_intervals<'tcx>( 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. - VisitPlacesWith(|place, ctxt| match DefUse::for_place(place, ctxt) { - DefUse::Def | DefUse::PartialWrite => { - if let Some(relevant) = relevant.shrink[place.local] { - values.insert(relevant, twostep); + let is_simple_assignment = + matches!(stmt.kind, StatementKind::Assign(box (_, Rvalue::Use(_)))); + VisitPlacesWith(|place: Place<'tcx>, ctxt| { + if let Some(relevant) = relevant.shrink[place.local] { + match DefUse::for_place(place, ctxt) { + DefUse::Def | DefUse::PartialWrite => { + values.insert(relevant, twostep); + } + DefUse::Use if !is_simple_assignment => { + values.insert(relevant, twostep); + } + DefUse::Use | DefUse::NonUse => {} } } - DefUse::Use | DefUse::NonUse => {} }) .visit_statement(stmt, loc); -- cgit 1.4.1-3-g733a5 From 8811344f22e0c015aaa45367b6462e3ecdcb22b5 Mon Sep 17 00:00:00 2001 From: Camille Gillot Date: Sun, 14 Sep 2025 13:04:53 +0000 Subject: Elaborate comment. --- compiler/rustc_mir_transform/src/dest_prop.rs | 8 ++++++-- 1 file changed, 6 insertions(+), 2 deletions(-) (limited to 'compiler') diff --git a/compiler/rustc_mir_transform/src/dest_prop.rs b/compiler/rustc_mir_transform/src/dest_prop.rs index 7e6f39881b8..b9ab0a9feee 100644 --- a/compiler/rustc_mir_transform/src/dest_prop.rs +++ b/compiler/rustc_mir_transform/src/dest_prop.rs @@ -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| { -- cgit 1.4.1-3-g733a5 From d58061e6131f6141985faadb6794af540f81b1db Mon Sep 17 00:00:00 2001 From: Camille Gillot Date: Tue, 16 Sep 2025 01:22:10 +0000 Subject: Restrict simple assignment condition. --- compiler/rustc_mir_transform/src/dest_prop.rs | 10 ++++++++-- 1 file changed, 8 insertions(+), 2 deletions(-) (limited to 'compiler') diff --git a/compiler/rustc_mir_transform/src/dest_prop.rs b/compiler/rustc_mir_transform/src/dest_prop.rs index b9ab0a9feee..c57483a6811 100644 --- a/compiler/rustc_mir_transform/src/dest_prop.rs +++ b/compiler/rustc_mir_transform/src/dest_prop.rs @@ -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) { -- cgit 1.4.1-3-g733a5