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Merged
merged 2 commits into from
Jul 6, 2025
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Merged

Do not unify borrowed locals in CopyProp. #143509

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bab9c75
Do not unify borrowed locals in CopyProp.
cjgillot Jul 5, 2025
b1fdb4b
Do not optimize stable-mir ui tests.
cjgillot Jul 6, 2025
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4 changes: 2 additions & 2 deletions compiler/rustc_mir_transform/src/ssa.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -322,8 +322,8 @@ fn compute_copy_classes(ssa: &mut SsaLocals, body: &Body<'_>) {
// visited before `local`, and we just have to copy the representing local.
let head = copies[rhs];

// Do not unify two borrowed locals.
if borrowed_classes.contains(local) && borrowed_classes.contains(head) {
// Do not unify borrowed locals.
if borrowed_classes.contains(local) || borrowed_classes.contains(head) {
continue;
}

Expand Down
101 changes: 101 additions & 0 deletions tests/mir-opt/copy-prop/borrowed_local.borrow_in_loop.CopyProp.panic-abort.diff
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Original file line number Diff line number Diff line change
@@ -0,0 +1,101 @@
- // MIR for `borrow_in_loop` before CopyProp
+ // MIR for `borrow_in_loop` after CopyProp

fn borrow_in_loop() -> () {
let mut _0: ();
let mut _1: bool;
let _3: bool;
let mut _4: !;
let mut _5: ();
let mut _7: bool;
let mut _9: bool;
let mut _10: bool;
let mut _11: &bool;
let _12: &bool;
let mut _13: bool;
let mut _14: bool;
let mut _15: bool;
let mut _16: !;
scope 1 {
debug c => _1;
let mut _2: &bool;
let mut _17: &bool;
scope 2 {
debug p => _2;
let _6: bool;
scope 3 {
debug a => _6;
let _8: bool;
scope 4 {
debug b => _8;
}
}
}
}

bb0: {
StorageLive(_1);
StorageLive(_2);
_17 = const borrow_in_loop::promoted[0];
_2 = &(*_17);
- StorageLive(_4);
goto -> bb1;
}

bb1: {
- StorageLive(_6);
StorageLive(_7);
_7 = copy (*_2);
_6 = Not(move _7);
StorageDead(_7);
- StorageLive(_8);
StorageLive(_9);
_9 = copy (*_2);
_8 = Not(move _9);
StorageDead(_9);
- StorageLive(_10);
- _10 = copy _6;
- _1 = move _10;
- StorageDead(_10);
+ _1 = copy _6;
StorageLive(_11);
StorageLive(_12);
_12 = &_1;
_11 = &(*_12);
_2 = move _11;
StorageDead(_11);
StorageDead(_12);
StorageLive(_13);
- StorageLive(_14);
- _14 = copy _6;
- StorageLive(_15);
- _15 = copy _8;
- _13 = Ne(move _14, move _15);
+ _13 = Ne(copy _6, copy _8);
switchInt(move _13) -> [0: bb3, otherwise: bb2];
}

bb2: {
- StorageDead(_15);
- StorageDead(_14);
_0 = const ();
StorageDead(_13);
- StorageDead(_8);
- StorageDead(_6);
- StorageDead(_4);
StorageDead(_2);
StorageDead(_1);
return;
}

bb3: {
- StorageDead(_15);
- StorageDead(_14);
- _5 = const ();
StorageDead(_13);
- StorageDead(_8);
- StorageDead(_6);
goto -> bb1;
}
}

101 changes: 101 additions & 0 deletions tests/mir-opt/copy-prop/borrowed_local.borrow_in_loop.CopyProp.panic-unwind.diff
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Original file line number Diff line number Diff line change
@@ -0,0 +1,101 @@
- // MIR for `borrow_in_loop` before CopyProp
+ // MIR for `borrow_in_loop` after CopyProp

fn borrow_in_loop() -> () {
let mut _0: ();
let mut _1: bool;
let _3: bool;
let mut _4: !;
let mut _5: ();
let mut _7: bool;
let mut _9: bool;
let mut _10: bool;
let mut _11: &bool;
let _12: &bool;
let mut _13: bool;
let mut _14: bool;
let mut _15: bool;
let mut _16: !;
scope 1 {
debug c => _1;
let mut _2: &bool;
let mut _17: &bool;
scope 2 {
debug p => _2;
let _6: bool;
scope 3 {
debug a => _6;
let _8: bool;
scope 4 {
debug b => _8;
}
}
}
}

bb0: {
StorageLive(_1);
StorageLive(_2);
_17 = const borrow_in_loop::promoted[0];
_2 = &(*_17);
- StorageLive(_4);
goto -> bb1;
}

bb1: {
- StorageLive(_6);
StorageLive(_7);
_7 = copy (*_2);
_6 = Not(move _7);
StorageDead(_7);
- StorageLive(_8);
StorageLive(_9);
_9 = copy (*_2);
_8 = Not(move _9);
StorageDead(_9);
- StorageLive(_10);
- _10 = copy _6;
- _1 = move _10;
- StorageDead(_10);
+ _1 = copy _6;
StorageLive(_11);
StorageLive(_12);
_12 = &_1;
_11 = &(*_12);
_2 = move _11;
StorageDead(_11);
StorageDead(_12);
StorageLive(_13);
- StorageLive(_14);
- _14 = copy _6;
- StorageLive(_15);
- _15 = copy _8;
- _13 = Ne(move _14, move _15);
+ _13 = Ne(copy _6, copy _8);
switchInt(move _13) -> [0: bb3, otherwise: bb2];
}

bb2: {
- StorageDead(_15);
- StorageDead(_14);
_0 = const ();
StorageDead(_13);
- StorageDead(_8);
- StorageDead(_6);
- StorageDead(_4);
StorageDead(_2);
StorageDead(_1);
return;
}

bb3: {
- StorageDead(_15);
- StorageDead(_14);
- _5 = const ();
StorageDead(_13);
- StorageDead(_8);
- StorageDead(_6);
goto -> bb1;
}
}

5 changes: 2 additions & 3 deletions tests/mir-opt/copy-prop/borrowed_local.borrowed.CopyProp.panic-abort.diff
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Original file line number Diff line number Diff line change
Expand Up @@ -7,14 +7,13 @@
let mut _3: &T;

bb0: {
- _2 = copy _1;
_2 = copy _1;
_3 = &_1;
_0 = opaque::<&T>(copy _3) -> [return: bb1, unwind unreachable];
}

bb1: {
- _0 = opaque::<T>(copy _2) -> [return: bb2, unwind unreachable];
+ _0 = opaque::<T>(copy _1) -> [return: bb2, unwind unreachable];
_0 = opaque::<T>(copy _2) -> [return: bb2, unwind unreachable];
}

bb2: {
Expand Down
5 changes: 2 additions & 3 deletions tests/mir-opt/copy-prop/borrowed_local.borrowed.CopyProp.panic-unwind.diff
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Original file line number Diff line number Diff line change
Expand Up @@ -7,14 +7,13 @@
let mut _3: &T;

bb0: {
- _2 = copy _1;
_2 = copy _1;
_3 = &_1;
_0 = opaque::<&T>(copy _3) -> [return: bb1, unwind continue];
}

bb1: {
- _0 = opaque::<T>(copy _2) -> [return: bb2, unwind continue];
+ _0 = opaque::<T>(copy _1) -> [return: bb2, unwind continue];
_0 = opaque::<T>(copy _2) -> [return: bb2, unwind continue];
}

bb2: {
Expand Down
37 changes: 36 additions & 1 deletion tests/mir-opt/copy-prop/borrowed_local.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -50,10 +50,11 @@ fn compare_address() -> bool {
fn borrowed<T: Copy + Freeze>(x: T) -> bool {
// CHECK-LABEL: fn borrowed(
// CHECK: bb0: {
// CHECK-NEXT: _2 = copy _1;
// CHECK-NEXT: _3 = &_1;
// CHECK-NEXT: _0 = opaque::<&T>(copy _3)
// CHECK: bb1: {
// CHECK-NEXT: _0 = opaque::<T>(copy _1)
// CHECK-NEXT: _0 = opaque::<T>(copy _2)
mir! {
{
let a = x;
Expand Down Expand Up @@ -94,11 +95,45 @@ fn non_freeze<T: Copy>(x: T) -> bool {
}
}

/// We must not unify a borrowed local with another that may be written-to before the borrow is
/// read again. As we have no aliasing model yet, this means forbidding unifying borrowed locals.
fn borrow_in_loop() {
// CHECK-LABEL: fn borrow_in_loop(
// CHECK: debug c => [[c:_.*]];
// CHECK: debug p => [[p:_.*]];
// CHECK: debug a => [[a:_.*]];
// CHECK: debug b => [[b:_.*]];
// CHECK-NOT: &[[a]]
// CHECK-NOT: &[[b]]
// CHECK: [[a]] = Not({{.*}});
// CHECK-NOT: &[[a]]
// CHECK-NOT: &[[b]]
// CHECK: [[b]] = Not({{.*}});
// CHECK-NOT: &[[a]]
// CHECK-NOT: &[[b]]
// CHECK: &[[c]]
// CHECK-NOT: &[[a]]
// CHECK-NOT: &[[b]]
let mut c;
let mut p = &false;
loop {
let a = !*p;
let b = !*p;
c = a;
p = &c;
if a != b {
return;
}
}
}

fn main() {
assert!(!compare_address());
non_freeze(5);
borrow_in_loop();
}

// EMIT_MIR borrowed_local.compare_address.CopyProp.diff
// EMIT_MIR borrowed_local.borrowed.CopyProp.diff
// EMIT_MIR borrowed_local.non_freeze.CopyProp.diff
// EMIT_MIR borrowed_local.borrow_in_loop.CopyProp.diff
5 changes: 2 additions & 3 deletions tests/mir-opt/copy-prop/write_to_borrowed.main.CopyProp.diff
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Original file line number Diff line number Diff line change
Expand Up @@ -16,11 +16,10 @@
_3 = const 'b';
_5 = copy _3;
_6 = &_3;
- _4 = copy _5;
_4 = copy _5;
(*_1) = copy (*_6);
_6 = &_5;
- _7 = dump_var::<char>(copy _4) -> [return: bb1, unwind unreachable];
+ _7 = dump_var::<char>(copy _5) -> [return: bb1, unwind unreachable];
_7 = dump_var::<char>(copy _4) -> [return: bb1, unwind unreachable];
}

bb1: {
Expand Down
4 changes: 2 additions & 2 deletions tests/mir-opt/copy-prop/write_to_borrowed.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -27,13 +27,13 @@ fn main() {
_5 = _3;
// CHECK-NEXT: _6 = &_3;
_6 = &_3;
// CHECK-NOT: {{_.*}} = {{_.*}};
// CHECK-NEXT: _4 = copy _5;
_4 = _5;
// CHECK-NEXT: (*_1) = copy (*_6);
*_1 = *_6;
// CHECK-NEXT: _6 = &_5;
_6 = &_5;
// CHECK-NEXT: _7 = dump_var::<char>(copy _5)
// CHECK-NEXT: _7 = dump_var::<char>(copy _4)
Call(_7 = dump_var(_4), ReturnTo(bb1), UnwindUnreachable())
}
bb1 = { Return() }
Expand Down
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