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Propagate from borrowed locals in CopyProp

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This commit is contained in:
Tomasz Miąsko
2025-07-07 21:49:20 +02:00
parent 32cd911471
commit 9681786409
7 changed files with 98 additions and 143 deletions
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compiler/rustc_mir_transform/src/ssa.rs
+6 -20
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@@ -293,10 +293,6 @@ fn visit_place(&mut self, place: &Place<'tcx>, ctxt: PlaceContext, loc: Location
fn compute_copy_classes(ssa: &mut SsaLocals, body: &Body<'_>) {
let mut direct_uses = std::mem::take(&mut ssa.direct_uses);
let mut copies = IndexVec::from_fn_n(|l| l, body.local_decls.len());
// We must not unify two locals that are borrowed. But this is fine if one is borrowed and
// the other is not. This bitset is keyed by *class head* and contains whether any member of
// the class is borrowed.
let mut borrowed_classes = ssa.borrowed_locals().clone();
for (local, rvalue, _) in ssa.assignments(body) {
let (Rvalue::Use(Operand::Copy(place) | Operand::Move(place))
@@ -322,8 +318,12 @@ 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 borrowed locals.
if borrowed_classes.contains(local) || borrowed_classes.contains(head) {
// When propagating from `head` to `local` we need to ensure that changes to the address
// are not observable, so at most one the locals involved can be borrowed. Additionally, we
// need to ensure that the definition of `head` dominates all uses of `local`. When `local`
// is borrowed, there might exist an indirect use of `local` that isn't dominated by the
// definition, so we have to reject copy propagation.
if ssa.borrowed_locals().contains(local) {
continue;
}
@@ -339,21 +339,14 @@ fn compute_copy_classes(ssa: &mut SsaLocals, body: &Body<'_>) {
*h = RETURN_PLACE;
}
}
if borrowed_classes.contains(head) {
borrowed_classes.insert(RETURN_PLACE);
}
} else {
copies[local] = head;
if borrowed_classes.contains(local) {
borrowed_classes.insert(head);
}
}
direct_uses[rhs] -= 1;
}
debug!(?copies);
debug!(?direct_uses);
debug!(?borrowed_classes);
// Invariant: `copies` must point to the head of an equivalence class.
#[cfg(debug_assertions)]
@@ -362,13 +355,6 @@ fn compute_copy_classes(ssa: &mut SsaLocals, body: &Body<'_>) {
}
debug_assert_eq!(copies[RETURN_PLACE], RETURN_PLACE);
// Invariant: `borrowed_classes` must be true if any member of the class is borrowed.
#[cfg(debug_assertions)]
for &head in copies.iter() {
let any_borrowed = ssa.borrowed_locals.iter().any(|l| copies[l] == head);
assert_eq!(borrowed_classes.contains(head), any_borrowed);
}
ssa.direct_uses = direct_uses;
ssa.copy_classes = copies;
}
tests/mir-opt/copy-prop/borrowed_local.borrowed.CopyProp.panic-abort.diff
+3 -2
View File
@@ -7,13 +7,14 @@
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 _2) -> [return: bb2, unwind unreachable];
+ _0 = opaque::<T>(copy _1) -> [return: bb2, unwind unreachable];
}
bb2: {
tests/mir-opt/copy-prop/borrowed_local.borrowed.CopyProp.panic-unwind.diff
+3 -2
View File
@@ -7,13 +7,14 @@
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 _2) -> [return: bb2, unwind continue];
+ _0 = opaque::<T>(copy _1) -> [return: bb2, unwind continue];
}
bb2: {
tests/mir-opt/copy-prop/borrowed_local.rs
+1 -2
View File
@@ -50,11 +50,10 @@ 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 _2)
// CHECK-NEXT: _0 = opaque::<T>(copy _1)
mir! {
{
let a = x;
tests/mir-opt/copy-prop/write_to_borrowed.main.CopyProp.diff
+3 -2
View File
@@ -16,10 +16,11 @@
_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 _4) -> [return: bb1, unwind unreachable];
+ _7 = dump_var::<char>(copy _5) -> [return: bb1, unwind unreachable];
}
bb1: {
tests/mir-opt/copy-prop/write_to_borrowed.rs
+1 -2
View File
@@ -27,13 +27,12 @@ fn main() {
_5 = _3;
// CHECK-NEXT: _6 = &_3;
_6 = &_3;
// 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 _4)
// CHECK-NEXT: _7 = dump_var::<char>(copy _5)
Call(_7 = dump_var(_4), ReturnTo(bb1), UnwindUnreachable())
}
bb1 = { Return() }
tests/mir-opt/pre-codegen/slice_filter.variant_a-{closure#0}.PreCodegen.after.mir
+81 -113
View File
@@ -10,18 +10,18 @@ fn variant_a::{closure#0}(_1: &mut {closure@$DIR/slice_filter.rs:7:25: 7:39}, _2
let mut _8: &&usize;
let _9: &usize;
let mut _10: &&usize;
let mut _15: bool;
let mut _13: bool;
let mut _14: &&usize;
let _15: &usize;
let mut _16: &&usize;
let _17: &usize;
let mut _18: &&usize;
let mut _19: bool;
let mut _20: &&usize;
let _21: &usize;
let mut _22: &&usize;
let mut _23: bool;
let mut _24: &&usize;
let _25: &usize;
let mut _26: &&usize;
let mut _29: bool;
let mut _30: &&usize;
let _31: &usize;
let mut _32: &&usize;
scope 1 {
debug a => _4;
debug b => _5;
@@ -30,47 +30,39 @@ fn variant_a::{closure#0}(_1: &mut {closure@$DIR/slice_filter.rs:7:25: 7:39}, _2
scope 2 (inlined std::cmp::impls::<impl PartialOrd for &usize>::le) {
debug self => _8;
debug other => _10;
let mut _11: &usize;
let mut _12: &usize;
scope 3 (inlined std::cmp::impls::<impl PartialOrd for usize>::le) {
debug self => _11;
debug other => _12;
let mut _13: usize;
let mut _14: usize;
debug self => _4;
debug other => _6;
let mut _11: usize;
let mut _12: usize;
}
}
scope 4 (inlined std::cmp::impls::<impl PartialOrd for &usize>::le) {
debug self => _16;
debug other => _18;
let mut _19: &usize;
let mut _20: &usize;
debug self => _14;
debug other => _16;
scope 5 (inlined std::cmp::impls::<impl PartialOrd for usize>::le) {
debug self => _19;
debug other => _20;
let mut _21: usize;
let mut _22: usize;
debug self => _7;
debug other => _5;
let mut _17: usize;
let mut _18: usize;
}
}
scope 6 (inlined std::cmp::impls::<impl PartialOrd for &usize>::le) {
debug self => _24;
debug other => _26;
let mut _27: &usize;
let mut _28: &usize;
debug self => _20;
debug other => _22;
scope 7 (inlined std::cmp::impls::<impl PartialOrd for usize>::le) {
debug self => _27;
debug other => _28;
debug self => _6;
debug other => _4;
}
}
scope 8 (inlined std::cmp::impls::<impl PartialOrd for &usize>::le) {
debug self => _30;
debug other => _32;
let mut _33: &usize;
let mut _34: &usize;
debug self => _24;
debug other => _26;
scope 9 (inlined std::cmp::impls::<impl PartialOrd for usize>::le) {
debug self => _33;
debug other => _34;
let mut _35: usize;
let mut _36: usize;
debug self => _5;
debug other => _7;
let mut _27: usize;
let mut _28: usize;
}
}
}
@@ -81,23 +73,17 @@ fn variant_a::{closure#0}(_1: &mut {closure@$DIR/slice_filter.rs:7:25: 7:39}, _2
_5 = &((*_3).1: usize);
_6 = &((*_3).2: usize);
_7 = &((*_3).3: usize);
StorageLive(_15);
StorageLive(_13);
StorageLive(_8);
_8 = &_4;
StorageLive(_10);
StorageLive(_9);
_9 = copy _6;
_10 = &_9;
StorageLive(_11);
StorageLive(_12);
_11 = copy _4;
_12 = copy _6;
_13 = copy ((*_3).0: usize);
_14 = copy ((*_3).2: usize);
_15 = Le(copy _13, copy _14);
StorageDead(_12);
StorageDead(_11);
switchInt(move _15) -> [0: bb1, otherwise: bb2];
_11 = copy ((*_3).0: usize);
_12 = copy ((*_3).2: usize);
_13 = Le(copy _11, copy _12);
switchInt(move _13) -> [0: bb1, otherwise: bb2];
}
bb1: {
@@ -111,107 +97,89 @@ fn variant_a::{closure#0}(_1: &mut {closure@$DIR/slice_filter.rs:7:25: 7:39}, _2
StorageDead(_9);
StorageDead(_10);
StorageDead(_8);
StorageLive(_23);
StorageLive(_16);
_16 = &_7;
StorageLive(_18);
StorageLive(_17);
_17 = copy _5;
_18 = &_17;
StorageLive(_19);
StorageLive(_20);
_19 = copy _7;
_20 = copy _5;
StorageLive(_21);
_21 = copy ((*_3).3: usize);
StorageLive(_22);
_22 = copy ((*_3).1: usize);
_23 = Le(move _21, move _22);
StorageDead(_22);
StorageDead(_21);
StorageDead(_20);
StorageDead(_19);
switchInt(move _23) -> [0: bb3, otherwise: bb8];
StorageLive(_14);
_14 = &_7;
StorageLive(_16);
StorageLive(_15);
_15 = copy _5;
_16 = &_15;
StorageLive(_17);
_17 = copy ((*_3).3: usize);
StorageLive(_18);
_18 = copy ((*_3).1: usize);
_19 = Le(move _17, move _18);
StorageDead(_18);
StorageDead(_17);
switchInt(move _19) -> [0: bb3, otherwise: bb8];
}
bb3: {
StorageDead(_17);
StorageDead(_18);
StorageDead(_15);
StorageDead(_16);
StorageDead(_14);
goto -> bb4;
}
bb4: {
StorageLive(_29);
StorageLive(_24);
_24 = &_6;
StorageLive(_26);
StorageLive(_25);
_25 = copy _4;
_26 = &_25;
StorageLive(_27);
StorageLive(_28);
_27 = copy _6;
_28 = copy _4;
_29 = Le(copy _14, copy _13);
StorageDead(_28);
StorageDead(_27);
switchInt(move _29) -> [0: bb5, otherwise: bb6];
StorageLive(_23);
StorageLive(_20);
_20 = &_6;
StorageLive(_22);
StorageLive(_21);
_21 = copy _4;
_22 = &_21;
_23 = Le(copy _12, copy _11);
switchInt(move _23) -> [0: bb5, otherwise: bb6];
}
bb5: {
StorageDead(_25);
StorageDead(_26);
StorageDead(_24);
StorageDead(_21);
StorageDead(_22);
StorageDead(_20);
_0 = const false;
goto -> bb7;
}
bb6: {
StorageDead(_21);
StorageDead(_22);
StorageDead(_20);
StorageLive(_24);
_24 = &_5;
StorageLive(_26);
StorageLive(_25);
_25 = copy _7;
_26 = &_25;
StorageLive(_27);
_27 = copy ((*_3).1: usize);
StorageLive(_28);
_28 = copy ((*_3).3: usize);
_0 = Le(move _27, move _28);
StorageDead(_28);
StorageDead(_27);
StorageDead(_25);
StorageDead(_26);
StorageDead(_24);
StorageLive(_30);
_30 = &_5;
StorageLive(_32);
StorageLive(_31);
_31 = copy _7;
_32 = &_31;
StorageLive(_33);
StorageLive(_34);
_33 = copy _5;
_34 = copy _7;
StorageLive(_35);
_35 = copy ((*_3).1: usize);
StorageLive(_36);
_36 = copy ((*_3).3: usize);
_0 = Le(move _35, move _36);
StorageDead(_36);
StorageDead(_35);
StorageDead(_34);
StorageDead(_33);
StorageDead(_31);
StorageDead(_32);
StorageDead(_30);
goto -> bb7;
}
bb7: {
StorageDead(_29);
StorageDead(_23);
goto -> bb9;
}
bb8: {
StorageDead(_17);
StorageDead(_18);
StorageDead(_15);
StorageDead(_16);
StorageDead(_14);
_0 = const true;
goto -> bb9;
}
bb9: {
StorageDead(_23);
StorageDead(_15);
StorageDead(_19);
StorageDead(_13);
return;
}
}