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Convert moves of references to copies in ReferencePropagation #142185

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e41bd6c
Convert moves of references to copies in RefProp
saethlin Jun 7, 2025
d432379
Add a test
saethlin Jun 8, 2025
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34 changes: 31 additions & 3 deletions compiler/rustc_mir_transform/src/ref_prop.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -79,6 +79,7 @@ impl<'tcx> crate::MirPass<'tcx> for ReferencePropagation {
#[instrument(level = "trace", skip(self, tcx, body))]
fn run_pass(&self, tcx: TyCtxt<'tcx>, body: &mut Body<'tcx>) {
debug!(def_id = ?body.source.def_id());
move_to_copy_pointers(tcx, body);
while propagate_ssa(tcx, body) {}
}

Expand All @@ -87,11 +88,38 @@ impl<'tcx> crate::MirPass<'tcx> for ReferencePropagation {
}
}

fn move_to_copy_pointers<'tcx>(tcx: TyCtxt<'tcx>, body: &mut Body<'tcx>) {
let mut visitor = MoveToCopyVisitor { tcx, local_decls: &body.local_decls };
for (bb, data) in body.basic_blocks.as_mut_preserves_cfg().iter_enumerated_mut() {
visitor.visit_basic_block_data(bb, data);
}

struct MoveToCopyVisitor<'a, 'tcx> {
tcx: TyCtxt<'tcx>,
local_decls: &'a IndexVec<Local, LocalDecl<'tcx>>,
}

impl<'a, 'tcx> MutVisitor<'tcx> for MoveToCopyVisitor<'a, 'tcx> {
fn tcx(&self) -> TyCtxt<'tcx> {
self.tcx
}

fn visit_operand(&mut self, operand: &mut Operand<'tcx>, loc: Location) {
if let Operand::Move(place) = *operand {
if place.ty(self.local_decls, self.tcx).ty.is_any_ptr() {
*operand = Operand::Copy(place);
}
}
self.super_operand(operand, loc);
}
}
}

fn propagate_ssa<'tcx>(tcx: TyCtxt<'tcx>, body: &mut Body<'tcx>) -> bool {
let typing_env = body.typing_env(tcx);
let ssa = SsaLocals::new(tcx, body, typing_env);

let mut replacer = compute_replacement(tcx, body, &ssa);
let mut replacer = compute_replacement(tcx, body, ssa);
debug!(?replacer.targets);
debug!(?replacer.allowed_replacements);
debug!(?replacer.storage_to_remove);
Expand Down Expand Up @@ -119,7 +147,7 @@ enum Value<'tcx> {
fn compute_replacement<'tcx>(
tcx: TyCtxt<'tcx>,
body: &Body<'tcx>,
ssa: &SsaLocals,
ssa: SsaLocals,
) -> Replacer<'tcx> {
let always_live_locals = always_storage_live_locals(body);

Expand All @@ -138,7 +166,7 @@ fn compute_replacement<'tcx>(
// reborrowed references.
let mut storage_to_remove = DenseBitSet::new_empty(body.local_decls.len());

let fully_replacable_locals = fully_replacable_locals(ssa);
let fully_replacable_locals = fully_replacable_locals(&ssa);

// Returns true iff we can use `place` as a pointee.
//
Expand Down
2 changes: 1 addition & 1 deletion tests/mir-opt/building/index_array_and_slice.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -55,7 +55,7 @@ struct WithSliceTail(f64, [i32]);
fn index_custom(custom: &WithSliceTail, index: usize) -> &i32 {
// CHECK: bb0:
// CHECK: [[PTR:_.+]] = &raw const (fake) ((*_1).1: [i32]);
// CHECK: [[LEN:_.+]] = PtrMetadata(move [[PTR]]);
// CHECK: [[LEN:_.+]] = PtrMetadata(copy [[PTR]]);
// CHECK: [[LT:_.+]] = Lt(copy _2, copy [[LEN]]);
// CHECK: assert(move [[LT]], "index out of bounds{{.+}}", move [[LEN]], copy _2) -> [success: bb1,

Expand Down
2 changes: 1 addition & 1 deletion .../mir-opt/pre-codegen/issue_117368_print_invalid_constant.main.GVN.64bit.panic-unwind.diff
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Original file line number Diff line number Diff line change
Expand Up @@ -46,7 +46,7 @@
StorageDead(_6);
_4 = copy _5 as *mut [u8] (Transmute);
StorageDead(_5);
_3 = move _4 as *mut u8 (PtrToPtr);
_3 = copy _4 as *mut u8 (PtrToPtr);
StorageDead(_4);
StorageDead(_3);
- StorageDead(_1);
Expand Down
2 changes: 1 addition & 1 deletion tests/mir-opt/pre-codegen/slice_index.slice_get_mut_usize.PreCodegen.after.panic-unwind.mir
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Original file line number Diff line number Diff line change
Expand Up @@ -30,7 +30,7 @@ fn slice_get_mut_usize(_1: &mut [u32], _2: usize) -> Option<&mut u32> {
StorageDead(_3);
StorageLive(_5);
_5 = &mut (*_1)[_2];
_0 = Option::<&mut u32>::Some(move _5);
_0 = Option::<&mut u32>::Some(copy _5);
StorageDead(_5);
goto -> bb3;
}
Expand Down
3 changes: 2 additions & 1 deletion tests/mir-opt/reference_prop.debuginfo.ReferencePropagation.diff
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Original file line number Diff line number Diff line change
Expand Up @@ -99,7 +99,8 @@
_13 = &(*_26);
StorageLive(_15);
_15 = RangeFull;
_12 = <[i32; 10] as Index<RangeFull>>::index(move _13, move _15) -> [return: bb5, unwind continue];
- _12 = <[i32; 10] as Index<RangeFull>>::index(move _13, move _15) -> [return: bb5, unwind continue];
+ _12 = <[i32; 10] as Index<RangeFull>>::index(copy _13, move _15) -> [return: bb5, unwind continue];
}

bb5: {
Expand Down
18 changes: 12 additions & 6 deletions tests/mir-opt/reference_prop.reference_propagation.ReferencePropagation.diff
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Original file line number Diff line number Diff line change
Expand Up @@ -218,8 +218,9 @@
- StorageLive(_14);
- _14 = &_11;
- _13 = &(*_14);
- _12 = move _13;
+ _13 = &_11;
_12 = move _13;
+ _12 = copy _13;
StorageDead(_13);
- StorageDead(_14);
StorageLive(_15);
Expand Down Expand Up @@ -252,7 +253,8 @@
StorageLive(_23);
StorageLive(_24);
_24 = copy _21;
_23 = opaque::<&&usize>(move _24) -> [return: bb3, unwind continue];
- _23 = opaque::<&&usize>(move _24) -> [return: bb3, unwind continue];
+ _23 = opaque::<&&usize>(copy _24) -> [return: bb3, unwind continue];
}

bb3: {
Expand All @@ -276,7 +278,8 @@
StorageLive(_30);
StorageLive(_31);
_31 = copy _28;
_30 = opaque::<*mut &usize>(move _31) -> [return: bb4, unwind continue];
- _30 = opaque::<*mut &usize>(move _31) -> [return: bb4, unwind continue];
+ _30 = opaque::<*mut &usize>(copy _31) -> [return: bb4, unwind continue];
}

bb4: {
Expand All @@ -299,7 +302,8 @@
StorageLive(_36);
StorageLive(_37);
_37 = copy _34;
_36 = opaque::<&usize>(move _37) -> [return: bb5, unwind continue];
- _36 = opaque::<&usize>(move _37) -> [return: bb5, unwind continue];
+ _36 = opaque::<&usize>(copy _37) -> [return: bb5, unwind continue];
}

bb5: {
Expand Down Expand Up @@ -328,7 +332,8 @@
StorageLive(_45);
StorageLive(_46);
_46 = copy _44;
_45 = opaque::<&usize>(move _46) -> [return: bb6, unwind continue];
- _45 = opaque::<&usize>(move _46) -> [return: bb6, unwind continue];
+ _45 = opaque::<&usize>(copy _46) -> [return: bb6, unwind continue];
}

bb6: {
Expand Down Expand Up @@ -368,8 +373,9 @@
- StorageLive(_55);
- _55 = &(*_1);
- _54 = &(*_55);
- _2 = move _54;
+ _54 = &(*_1);
_2 = move _54;
+ _2 = copy _54;
StorageDead(_54);
- StorageDead(_55);
StorageLive(_56);
Expand Down
18 changes: 12 additions & 6 deletions tests/mir-opt/reference_prop.reference_propagation_const_ptr.ReferencePropagation.diff
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Original file line number Diff line number Diff line change
Expand Up @@ -233,7 +233,8 @@
_12 = &raw const _10;
StorageLive(_13);
_13 = &raw const _11;
_12 = move _13;
- _12 = move _13;
+ _12 = copy _13;
StorageDead(_13);
StorageLive(_14);
_14 = copy (*_12);
Expand Down Expand Up @@ -265,7 +266,8 @@
StorageLive(_22);
StorageLive(_23);
_23 = copy _20;
_22 = opaque::<&*const usize>(move _23) -> [return: bb3, unwind continue];
- _22 = opaque::<&*const usize>(move _23) -> [return: bb3, unwind continue];
+ _22 = opaque::<&*const usize>(copy _23) -> [return: bb3, unwind continue];
}

bb3: {
Expand All @@ -289,7 +291,8 @@
StorageLive(_29);
StorageLive(_30);
_30 = copy _27;
_29 = opaque::<*mut *const usize>(move _30) -> [return: bb4, unwind continue];
- _29 = opaque::<*mut *const usize>(move _30) -> [return: bb4, unwind continue];
+ _29 = opaque::<*mut *const usize>(copy _30) -> [return: bb4, unwind continue];
}

bb4: {
Expand All @@ -312,7 +315,8 @@
StorageLive(_35);
StorageLive(_36);
_36 = copy _33;
_35 = opaque::<*const usize>(move _36) -> [return: bb5, unwind continue];
- _35 = opaque::<*const usize>(move _36) -> [return: bb5, unwind continue];
+ _35 = opaque::<*const usize>(copy _36) -> [return: bb5, unwind continue];
}

bb5: {
Expand Down Expand Up @@ -341,7 +345,8 @@
StorageLive(_44);
StorageLive(_45);
_45 = copy _43;
_44 = opaque::<*const usize>(move _45) -> [return: bb6, unwind continue];
- _44 = opaque::<*const usize>(move _45) -> [return: bb6, unwind continue];
+ _44 = opaque::<*const usize>(copy _45) -> [return: bb6, unwind continue];
}

bb6: {
Expand Down Expand Up @@ -379,7 +384,8 @@
_52 = &raw const (*_2);
StorageLive(_53);
_53 = &raw const (*_1);
_2 = move _53;
- _2 = move _53;
+ _2 = copy _53;
StorageDead(_53);
StorageLive(_54);
_54 = copy (*_52);
Expand Down
30 changes: 20 additions & 10 deletions tests/mir-opt/reference_prop.reference_propagation_mut.ReferencePropagation.diff
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Original file line number Diff line number Diff line change
Expand Up @@ -218,8 +218,9 @@
- StorageLive(_14);
- _14 = &mut _11;
- _13 = &mut (*_14);
- _12 = move _13;
+ _13 = &mut _11;
_12 = move _13;
+ _12 = copy _13;
StorageDead(_13);
- StorageDead(_14);
StorageLive(_15);
Expand Down Expand Up @@ -251,7 +252,8 @@
StorageLive(_23);
StorageLive(_24);
_24 = copy _21;
_23 = opaque::<&&mut usize>(move _24) -> [return: bb3, unwind continue];
- _23 = opaque::<&&mut usize>(move _24) -> [return: bb3, unwind continue];
+ _23 = opaque::<&&mut usize>(copy _24) -> [return: bb3, unwind continue];
}

bb3: {
Expand All @@ -275,7 +277,8 @@
StorageLive(_30);
StorageLive(_31);
_31 = copy _28;
_30 = opaque::<*mut &mut usize>(move _31) -> [return: bb4, unwind continue];
- _30 = opaque::<*mut &mut usize>(move _31) -> [return: bb4, unwind continue];
+ _30 = opaque::<*mut &mut usize>(copy _31) -> [return: bb4, unwind continue];
}

bb4: {
Expand All @@ -296,8 +299,10 @@
_35 = copy (*_34);
StorageLive(_36);
StorageLive(_37);
_37 = move _34;
_36 = opaque::<&mut usize>(move _37) -> [return: bb5, unwind continue];
- _37 = move _34;
- _36 = opaque::<&mut usize>(move _37) -> [return: bb5, unwind continue];
+ _37 = copy _34;
+ _36 = opaque::<&mut usize>(copy _37) -> [return: bb5, unwind continue];
}

bb5: {
Expand All @@ -316,15 +321,19 @@
StorageLive(_41);
_41 = copy (*_40);
StorageLive(_42);
_42 = move _40;
- _42 = move _40;
+ _42 = copy _40;
StorageLive(_43);
_43 = copy (*_42);
StorageLive(_44);
_44 = move _42;
- _44 = move _42;
+ _44 = copy _42;
StorageLive(_45);
StorageLive(_46);
_46 = move _44;
_45 = opaque::<&mut usize>(move _46) -> [return: bb6, unwind continue];
- _46 = move _44;
- _45 = opaque::<&mut usize>(move _46) -> [return: bb6, unwind continue];
+ _46 = copy _44;
+ _45 = opaque::<&mut usize>(copy _46) -> [return: bb6, unwind continue];
}

bb6: {
Expand Down Expand Up @@ -364,8 +373,9 @@
- StorageLive(_55);
- _55 = &mut (*_1);
- _54 = &mut (*_55);
- _2 = move _54;
+ _54 = &mut (*_1);
_2 = move _54;
+ _2 = copy _54;
StorageDead(_54);
- StorageDead(_55);
StorageLive(_56);
Expand Down
18 changes: 12 additions & 6 deletions tests/mir-opt/reference_prop.reference_propagation_mut_ptr.ReferencePropagation.diff
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Original file line number Diff line number Diff line change
Expand Up @@ -214,7 +214,8 @@
_12 = &raw mut _10;
StorageLive(_13);
_13 = &raw mut _11;
_12 = move _13;
- _12 = move _13;
+ _12 = copy _13;
StorageDead(_13);
StorageLive(_14);
_14 = copy (*_12);
Expand Down Expand Up @@ -245,7 +246,8 @@
StorageLive(_22);
StorageLive(_23);
_23 = copy _20;
_22 = opaque::<&*mut usize>(move _23) -> [return: bb3, unwind continue];
- _22 = opaque::<&*mut usize>(move _23) -> [return: bb3, unwind continue];
+ _22 = opaque::<&*mut usize>(copy _23) -> [return: bb3, unwind continue];
}

bb3: {
Expand All @@ -269,7 +271,8 @@
StorageLive(_29);
StorageLive(_30);
_30 = copy _27;
_29 = opaque::<*mut *mut usize>(move _30) -> [return: bb4, unwind continue];
- _29 = opaque::<*mut *mut usize>(move _30) -> [return: bb4, unwind continue];
+ _29 = opaque::<*mut *mut usize>(copy _30) -> [return: bb4, unwind continue];
}

bb4: {
Expand All @@ -291,7 +294,8 @@
StorageLive(_35);
StorageLive(_36);
_36 = copy _33;
_35 = opaque::<*mut usize>(move _36) -> [return: bb5, unwind continue];
- _35 = opaque::<*mut usize>(move _36) -> [return: bb5, unwind continue];
+ _35 = opaque::<*mut usize>(copy _36) -> [return: bb5, unwind continue];
}

bb5: {
Expand All @@ -318,7 +322,8 @@
StorageLive(_44);
StorageLive(_45);
_45 = copy _43;
_44 = opaque::<*mut usize>(move _45) -> [return: bb6, unwind continue];
- _44 = opaque::<*mut usize>(move _45) -> [return: bb6, unwind continue];
+ _44 = opaque::<*mut usize>(copy _45) -> [return: bb6, unwind continue];
}

bb6: {
Expand Down Expand Up @@ -356,7 +361,8 @@
_52 = &raw mut (*_2);
StorageLive(_53);
_53 = &raw mut (*_1);
_2 = move _53;
- _2 = move _53;
+ _2 = copy _53;
StorageDead(_53);
StorageLive(_54);
_54 = copy (*_52);
Expand Down
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