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GVN: Bail out if the address cannot be dereferenced. #147844

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GVN: Bail out if the address cannot be dereferenced. #147844

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8df9dbc
Add miscompiled test cases for GVN
dianqk Oct 18, 2025
5b2be88
GVN: Bail out if the address cannot be dereferenced.
dianqk Oct 18, 2025
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13 changes: 9 additions & 4 deletions compiler/rustc_mir_transform/src/gvn.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -795,7 +795,12 @@ impl<'body, 'a, 'tcx> VnState<'body, 'a, 'tcx> {
// The base is a pointer's deref, so we introduce the implicit deref.
AddressBase::Deref(reborrow) => {
let place_ty = PlaceTy::from_ty(self.ty(reborrow));
self.project(place_ty, reborrow, ProjectionElem::Deref)?
self.project(place_ty, reborrow, ProjectionElem::Deref).unwrap_or_else(|| {
// Insert a deref instead if `reborrow` cannot be dereferenced.
let projection_ty =
place_ty.projection_ty::<VnIndex>(self.tcx, ProjectionElem::Deref);
return (projection_ty, self.insert_deref(projection_ty.ty, reborrow));
})
}
};
for &proj in projection {
Expand All @@ -817,9 +822,9 @@ impl<'body, 'a, 'tcx> VnState<'body, 'a, 'tcx> {
if let Some(Mutability::Not) = place_ty.ty.ref_mutability()
&& projection_ty.ty.is_freeze(self.tcx, self.typing_env())
{
if let Value::Address { base, projection, .. } = self.get(value)
&& let Some(value) = self.dereference_address(base, projection)
{
if let Value::Address { base, projection, .. } = self.get(value) {
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@dianqk dianqk Oct 18, 2025

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I don't have a test for projection, but projection should also be able to invalidate values.

// Bail out if the address cannot be dereferenced.
let value = self.dereference_address(base, projection)?;
return Some((projection_ty, value));
}

Expand Down
6 changes: 4 additions & 2 deletions tests/mir-opt/gvn.dereferences.GVN.panic-abort.diff
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Expand Up @@ -108,7 +108,8 @@
_18 = &(*_1);
StorageLive(_19);
StorageLive(_20);
_20 = copy (*_18);
- _20 = copy (*_18);
+ _20 = copy (*_1);
_19 = opaque::<u32>(move _20) -> [return: bb7, unwind unreachable];
}

Expand All @@ -117,7 +118,8 @@
StorageDead(_19);
StorageLive(_21);
StorageLive(_22);
_22 = copy (*_18);
- _22 = copy (*_18);
+ _22 = copy (*_1);
_21 = opaque::<u32>(move _22) -> [return: bb8, unwind unreachable];
}

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6 changes: 4 additions & 2 deletions tests/mir-opt/gvn.dereferences.GVN.panic-unwind.diff
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Expand Up @@ -108,7 +108,8 @@
_18 = &(*_1);
StorageLive(_19);
StorageLive(_20);
_20 = copy (*_18);
- _20 = copy (*_18);
+ _20 = copy (*_1);
_19 = opaque::<u32>(move _20) -> [return: bb7, unwind continue];
}

Expand All @@ -117,7 +118,8 @@
StorageDead(_19);
StorageLive(_21);
StorageLive(_22);
_22 = copy (*_18);
- _22 = copy (*_18);
+ _22 = copy (*_1);
_21 = opaque::<u32>(move _22) -> [return: bb8, unwind continue];
}

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18 changes: 9 additions & 9 deletions tests/mir-opt/gvn.fn_pointers.GVN.panic-abort.diff
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Expand Up @@ -8,18 +8,18 @@
let mut _3: fn(u8) -> u8;
let _5: ();
let mut _6: fn(u8) -> u8;
let mut _9: {closure@$DIR/gvn.rs:617:19: 617:21};
let mut _9: {closure@$DIR/gvn.rs:616:19: 616:21};
let _10: ();
let mut _11: fn();
let mut _13: {closure@$DIR/gvn.rs:617:19: 617:21};
let mut _13: {closure@$DIR/gvn.rs:616:19: 616:21};
let _14: ();
let mut _15: fn();
scope 1 {
debug f => _1;
let _4: fn(u8) -> u8;
scope 2 {
debug g => _4;
let _7: {closure@$DIR/gvn.rs:617:19: 617:21};
let _7: {closure@$DIR/gvn.rs:616:19: 616:21};
scope 3 {
debug closure => _7;
let _8: fn();
Expand Down Expand Up @@ -62,16 +62,16 @@
StorageDead(_6);
StorageDead(_5);
- StorageLive(_7);
- _7 = {closure@$DIR/gvn.rs:617:19: 617:21};
- _7 = {closure@$DIR/gvn.rs:616:19: 616:21};
- StorageLive(_8);
+ nop;
+ _7 = const ZeroSized: {closure@$DIR/gvn.rs:617:19: 617:21};
+ _7 = const ZeroSized: {closure@$DIR/gvn.rs:616:19: 616:21};
+ nop;
StorageLive(_9);
- _9 = copy _7;
- _8 = move _9 as fn() (PointerCoercion(ClosureFnPointer(Safe), AsCast));
+ _9 = const ZeroSized: {closure@$DIR/gvn.rs:617:19: 617:21};
+ _8 = const ZeroSized: {closure@$DIR/gvn.rs:617:19: 617:21} as fn() (PointerCoercion(ClosureFnPointer(Safe), AsCast));
+ _9 = const ZeroSized: {closure@$DIR/gvn.rs:616:19: 616:21};
+ _8 = const ZeroSized: {closure@$DIR/gvn.rs:616:19: 616:21} as fn() (PointerCoercion(ClosureFnPointer(Safe), AsCast));
StorageDead(_9);
StorageLive(_10);
StorageLive(_11);
Expand All @@ -88,8 +88,8 @@
StorageLive(_13);
- _13 = copy _7;
- _12 = move _13 as fn() (PointerCoercion(ClosureFnPointer(Safe), AsCast));
+ _13 = const ZeroSized: {closure@$DIR/gvn.rs:617:19: 617:21};
+ _12 = const ZeroSized: {closure@$DIR/gvn.rs:617:19: 617:21} as fn() (PointerCoercion(ClosureFnPointer(Safe), AsCast));
+ _13 = const ZeroSized: {closure@$DIR/gvn.rs:616:19: 616:21};
+ _12 = const ZeroSized: {closure@$DIR/gvn.rs:616:19: 616:21} as fn() (PointerCoercion(ClosureFnPointer(Safe), AsCast));
StorageDead(_13);
StorageLive(_14);
StorageLive(_15);
Expand Down
18 changes: 9 additions & 9 deletions tests/mir-opt/gvn.fn_pointers.GVN.panic-unwind.diff
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Original file line number Diff line number Diff line change
Expand Up @@ -8,18 +8,18 @@
let mut _3: fn(u8) -> u8;
let _5: ();
let mut _6: fn(u8) -> u8;
let mut _9: {closure@$DIR/gvn.rs:617:19: 617:21};
let mut _9: {closure@$DIR/gvn.rs:616:19: 616:21};
let _10: ();
let mut _11: fn();
let mut _13: {closure@$DIR/gvn.rs:617:19: 617:21};
let mut _13: {closure@$DIR/gvn.rs:616:19: 616:21};
let _14: ();
let mut _15: fn();
scope 1 {
debug f => _1;
let _4: fn(u8) -> u8;
scope 2 {
debug g => _4;
let _7: {closure@$DIR/gvn.rs:617:19: 617:21};
let _7: {closure@$DIR/gvn.rs:616:19: 616:21};
scope 3 {
debug closure => _7;
let _8: fn();
Expand Down Expand Up @@ -62,16 +62,16 @@
StorageDead(_6);
StorageDead(_5);
- StorageLive(_7);
- _7 = {closure@$DIR/gvn.rs:617:19: 617:21};
- _7 = {closure@$DIR/gvn.rs:616:19: 616:21};
- StorageLive(_8);
+ nop;
+ _7 = const ZeroSized: {closure@$DIR/gvn.rs:617:19: 617:21};
+ _7 = const ZeroSized: {closure@$DIR/gvn.rs:616:19: 616:21};
+ nop;
StorageLive(_9);
- _9 = copy _7;
- _8 = move _9 as fn() (PointerCoercion(ClosureFnPointer(Safe), AsCast));
+ _9 = const ZeroSized: {closure@$DIR/gvn.rs:617:19: 617:21};
+ _8 = const ZeroSized: {closure@$DIR/gvn.rs:617:19: 617:21} as fn() (PointerCoercion(ClosureFnPointer(Safe), AsCast));
+ _9 = const ZeroSized: {closure@$DIR/gvn.rs:616:19: 616:21};
+ _8 = const ZeroSized: {closure@$DIR/gvn.rs:616:19: 616:21} as fn() (PointerCoercion(ClosureFnPointer(Safe), AsCast));
StorageDead(_9);
StorageLive(_10);
StorageLive(_11);
Expand All @@ -88,8 +88,8 @@
StorageLive(_13);
- _13 = copy _7;
- _12 = move _13 as fn() (PointerCoercion(ClosureFnPointer(Safe), AsCast));
+ _13 = const ZeroSized: {closure@$DIR/gvn.rs:617:19: 617:21};
+ _12 = const ZeroSized: {closure@$DIR/gvn.rs:617:19: 617:21} as fn() (PointerCoercion(ClosureFnPointer(Safe), AsCast));
+ _13 = const ZeroSized: {closure@$DIR/gvn.rs:616:19: 616:21};
+ _12 = const ZeroSized: {closure@$DIR/gvn.rs:616:19: 616:21} as fn() (PointerCoercion(ClosureFnPointer(Safe), AsCast));
StorageDead(_13);
StorageLive(_14);
StorageLive(_15);
Expand Down
5 changes: 2 additions & 3 deletions tests/mir-opt/gvn.rs
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Expand Up @@ -499,11 +499,10 @@ fn dereferences(t: &mut u32, u: &impl Copy, s: &S<u32>) {
unsafe { opaque(*z) };
unsafe { opaque(*z) };

// Do not reuse dereferences of `&Freeze`.
// CHECK: [[ref:_.*]] = &(*_1);
// CHECK: [[st7:_.*]] = copy (*[[ref]]);
// CHECK: [[st7:_.*]] = copy (*_1);
// CHECK: opaque::<u32>(move [[st7]])
// CHECK: [[st8:_.*]] = copy (*[[ref]]);
// CHECK: [[st8:_.*]] = copy (*_1);
// CHECK: opaque::<u32>(move [[st8]])
let z = &*t;
opaque(*z);
Expand Down
48 changes: 48 additions & 0 deletions tests/mir-opt/gvn_copy_aggregate.deref_nonssa.GVN.diff
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@@ -0,0 +1,48 @@
- // MIR for `deref_nonssa` before GVN
+ // MIR for `deref_nonssa` after GVN

fn deref_nonssa() -> Single {
let mut _0: Single;
let mut _1: Single;
let mut _4: Single;
let mut _5: u8;
scope 1 {
debug a => _1;
let _2: &Single;
scope 2 {
debug b => _2;
let _3: u8;
scope 3 {
debug c => _3;
}
}
}

bb0: {
StorageLive(_1);
- _1 = Single(const 0_u8);
+ _1 = const Single(0_u8);
StorageLive(_2);
_2 = &_1;
- StorageLive(_3);
+ nop;
_3 = copy ((*_2).0: u8);
StorageLive(_4);
- _4 = Single(const 1_u8);
- _1 = move _4;
+ _4 = const Single(1_u8);
+ _1 = const Single(1_u8);
StorageDead(_4);
StorageLive(_5);
_5 = copy _3;
- _0 = Single(move _5);
+ _0 = Single(copy _3);
StorageDead(_5);
- StorageDead(_3);
+ nop;
StorageDead(_2);
StorageDead(_1);
return;
}
}

16 changes: 16 additions & 0 deletions tests/mir-opt/gvn_copy_aggregate.rs
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Expand Up @@ -259,3 +259,19 @@ fn remove_storage_dead_from_index(f: fn() -> usize, v: [SameType; 5]) -> SameTyp
}
}
}

pub struct Single(u8);

// EMIT_MIR gvn_copy_aggregate.deref_nonssa.GVN.diff
fn deref_nonssa() -> Single {
// CHECK-LABEL: fn deref_nonssa(
// CHECK: debug c => [[C:_.*]];
// CHECK-NOT: _0 = copy (*_{{.*}});
// CHECK: _0 = Single(copy [[C]]);
let mut a = Single(0);
let b = &a;
let c = (*b).0;
a = Single(1);
// GVN shouldn't replace `Single(c)` with `*b`.
Single(c)
}
18 changes: 18 additions & 0 deletions tests/mir-opt/gvn_overlapping.copy_overlapping.GVN.diff
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@@ -0,0 +1,18 @@
- // MIR for `copy_overlapping` before GVN
+ // MIR for `copy_overlapping` after GVN

fn copy_overlapping() -> () {
let mut _0: ();
let mut _1: Adt;
let mut _2: u32;
let mut _3: &Adt;

bb0: {
((_1 as variant#1).0: u32) = const 0_u32;
_3 = &_1;
_2 = copy (((*_3) as variant#1).0: u32);
_1 = Adt::Some(copy _2);
return;
}
}

3 changes: 2 additions & 1 deletion tests/mir-opt/gvn_overlapping.overlapping.GVN.diff
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Original file line number Diff line number Diff line change
Expand Up @@ -10,7 +10,8 @@
bb0: {
_2 = &raw mut _1;
_4 = &(*_2);
_3 = copy (((*_4) as variant#1).0: u32);
- _3 = copy (((*_4) as variant#1).0: u32);
+ _3 = copy (((*_2) as variant#1).0: u32);
(*_2) = Adt::Some(copy _3);
return;
}
Expand Down
22 changes: 21 additions & 1 deletion tests/mir-opt/gvn_overlapping.rs
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Expand Up @@ -32,7 +32,7 @@ fn stable_projection(_1: (Adt,)) {
// CHECK-LABEL: fn stable_projection(
// CHECK: let mut _2: *mut Adt;
// CHECK: let mut _4: &Adt;
// CHECK: (_1.0: Adt) = copy (*_4);
// CHECK: (_1.0: Adt) = copy (*_2);
mir! {
let _2: *mut Adt;
let _3: u32;
Expand Down Expand Up @@ -64,6 +64,26 @@ fn fields(_1: (Adt, Adt)) {
}
}

// EMIT_MIR gvn_overlapping.copy_overlapping.GVN.diff
#[custom_mir(dialect = "runtime")]
fn copy_overlapping() {
// CHECK-LABEL: fn copy_overlapping(
// CHECK-NOT: _1 = copy (*_{{.*}});
// CHECK: _1 = Adt::Some(copy _2);
mir! {
let _1;
let _2;
let _3;
{
place!(Field(Variant(_1, 1), 0)) = 0u32;
_3 = &_1;
_2 = Field(Variant(*_3, 1), 0);
_1 = Adt::Some(_2);
Return()
}
}
}

fn main() {
overlapping(Adt::Some(0));
}
Expand Down
5 changes: 3 additions & 2 deletions tests/mir-opt/gvn_overlapping.stable_projection.GVN.diff
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Original file line number Diff line number Diff line change
Expand Up @@ -10,9 +10,10 @@
bb0: {
_2 = &raw mut (_1.0: Adt);
_4 = &(*_2);
_3 = copy (((*_4) as variant#1).0: u32);
- _3 = copy (((*_4) as variant#1).0: u32);
- (_1.0: Adt) = Adt::Some(copy _3);
+ (_1.0: Adt) = copy (*_4);
+ _3 = copy (((*_2) as variant#1).0: u32);
+ (_1.0: Adt) = copy (*_2);
return;
}
}
Expand Down
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