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Transmute from NonNull to pointer when elaborating a box deref (MCP807) #135182

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Jan 7, 2025
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Transmute from NonNull to pointer when elaborating a box deref (MCP807) #135182

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27 changes: 14 additions & 13 deletions compiler/rustc_mir_transform/src/elaborate_box_derefs.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -29,13 +29,8 @@ fn build_ptr_tys<'tcx>(
pub(super) fn build_projection<'tcx>(
unique_ty: Ty<'tcx>,
nonnull_ty: Ty<'tcx>,
ptr_ty: Ty<'tcx>,
) -> [PlaceElem<'tcx>; 3] {
[
PlaceElem::Field(FieldIdx::ZERO, unique_ty),
PlaceElem::Field(FieldIdx::ZERO, nonnull_ty),
PlaceElem::Field(FieldIdx::ZERO, ptr_ty),
]
) -> [PlaceElem<'tcx>; 2] {
[PlaceElem::Field(FieldIdx::ZERO, unique_ty), PlaceElem::Field(FieldIdx::ZERO, nonnull_ty)]
}

struct ElaborateBoxDerefVisitor<'a, 'tcx> {
Expand Down Expand Up @@ -75,10 +70,14 @@ impl<'a, 'tcx> MutVisitor<'tcx> for ElaborateBoxDerefVisitor<'a, 'tcx> {
self.patch.add_assign(
location,
Place::from(ptr_local),
Rvalue::Use(Operand::Copy(
Place::from(place.local)
.project_deeper(&build_projection(unique_ty, nonnull_ty, ptr_ty), tcx),
)),
Rvalue::Cast(
CastKind::Transmute,
Operand::Copy(
Place::from(place.local)
.project_deeper(&build_projection(unique_ty, nonnull_ty), tcx),
),
ptr_ty,
),
);

place.local = ptr_local;
Expand Down Expand Up @@ -133,8 +132,10 @@ impl<'tcx> crate::MirPass<'tcx> for ElaborateBoxDerefs {
let (unique_ty, nonnull_ty, ptr_ty) =
build_ptr_tys(tcx, boxed_ty, unique_did, nonnull_did);

new_projections
.extend_from_slice(&build_projection(unique_ty, nonnull_ty, ptr_ty));
new_projections.extend_from_slice(&build_projection(unique_ty, nonnull_ty));
// While we can't project into `NonNull<_>` in a basic block
// due to MCP#807, this is debug info where it's fine.
new_projections.push(PlaceElem::Field(FieldIdx::ZERO, ptr_ty));
new_projections.push(PlaceElem::Deref);
} else if let Some(new_projections) = new_projections.as_mut() {
// Keep building up our projections list once we've started it.
Expand Down
2 changes: 1 addition & 1 deletion tests/mir-opt/box_expr.rs
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Expand Up @@ -7,7 +7,7 @@
fn main() {
// CHECK-LABEL: fn main(
// CHECK: [[box:_.*]] = ShallowInitBox(
// CHECK: [[ptr:_.*]] = copy ((([[box]].0: std::ptr::Unique<S>).0: std::ptr::NonNull<S>).0: *const S);
// CHECK: [[ptr:_.*]] = copy (([[box]].0: std::ptr::Unique<S>).0: std::ptr::NonNull<S>) as *const S (Transmute);
// CHECK: (*[[ptr]]) = S::new() -> [return: [[ret:bb.*]], unwind: [[unwind:bb.*]]];
// CHECK: [[ret]]: {
// CHECK: [[box2:_.*]] = move [[box]];
Expand Down
4 changes: 2 additions & 2 deletions tests/mir-opt/const_prop/boxes.main.GVN.panic-abort.diff
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Expand Up @@ -32,11 +32,11 @@
bb1: {
StorageLive(_7);
_7 = ShallowInitBox(move _6, i32);
_8 = copy (((_7.0: std::ptr::Unique<i32>).0: std::ptr::NonNull<i32>).0: *const i32);
_8 = copy ((_7.0: std::ptr::Unique<i32>).0: std::ptr::NonNull<i32>) as *const i32 (Transmute);
(*_8) = const 42_i32;
_3 = move _7;
StorageDead(_7);
_9 = copy (((_3.0: std::ptr::Unique<i32>).0: std::ptr::NonNull<i32>).0: *const i32);
_9 = copy ((_3.0: std::ptr::Unique<i32>).0: std::ptr::NonNull<i32>) as *const i32 (Transmute);
_2 = copy (*_9);
- _1 = Add(move _2, const 0_i32);
- StorageDead(_2);
Expand Down
4 changes: 2 additions & 2 deletions tests/mir-opt/const_prop/boxes.main.GVN.panic-unwind.diff
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Expand Up @@ -32,11 +32,11 @@
bb1: {
StorageLive(_7);
_7 = ShallowInitBox(move _6, i32);
_8 = copy (((_7.0: std::ptr::Unique<i32>).0: std::ptr::NonNull<i32>).0: *const i32);
_8 = copy ((_7.0: std::ptr::Unique<i32>).0: std::ptr::NonNull<i32>) as *const i32 (Transmute);
(*_8) = const 42_i32;
_3 = move _7;
StorageDead(_7);
_9 = copy (((_3.0: std::ptr::Unique<i32>).0: std::ptr::NonNull<i32>).0: *const i32);
_9 = copy ((_3.0: std::ptr::Unique<i32>).0: std::ptr::NonNull<i32>) as *const i32 (Transmute);
_2 = copy (*_9);
- _1 = Add(move _2, const 0_i32);
- StorageDead(_2);
Expand Down
4 changes: 2 additions & 2 deletions tests/mir-opt/const_prop/transmute.unreachable_box.GVN.32bit.diff
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Expand Up @@ -12,9 +12,9 @@
bb0: {
StorageLive(_1);
- _1 = const 1_usize as std::boxed::Box<Never> (Transmute);
- _2 = copy (((_1.0: std::ptr::Unique<Never>).0: std::ptr::NonNull<Never>).0: *const Never);
- _2 = copy ((_1.0: std::ptr::Unique<Never>).0: std::ptr::NonNull<Never>) as *const Never (Transmute);
+ _1 = const Box::<Never>(Unique::<Never> {{ pointer: NonNull::<Never> {{ pointer: {0x1 as *const Never} }}, _marker: PhantomData::<Never> }}, std::alloc::Global);
+ _2 = const {0x1 as *const Never};
+ _2 = const std::ptr::NonNull::<Never> {{ pointer: {0x1 as *const Never} }} as *const Never (Transmute);
unreachable;
}
}
Expand Down
4 changes: 2 additions & 2 deletions tests/mir-opt/const_prop/transmute.unreachable_box.GVN.64bit.diff
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Expand Up @@ -12,9 +12,9 @@
bb0: {
StorageLive(_1);
- _1 = const 1_usize as std::boxed::Box<Never> (Transmute);
- _2 = copy (((_1.0: std::ptr::Unique<Never>).0: std::ptr::NonNull<Never>).0: *const Never);
- _2 = copy ((_1.0: std::ptr::Unique<Never>).0: std::ptr::NonNull<Never>) as *const Never (Transmute);
+ _1 = const Box::<Never>(Unique::<Never> {{ pointer: NonNull::<Never> {{ pointer: {0x1 as *const Never} }}, _marker: PhantomData::<Never> }}, std::alloc::Global);
+ _2 = const {0x1 as *const Never};
+ _2 = const std::ptr::NonNull::<Never> {{ pointer: {0x1 as *const Never} }} as *const Never (Transmute);
unreachable;
}
}
Expand Down
2 changes: 1 addition & 1 deletion tests/mir-opt/dataflow-const-prop/transmute.unreachable_box.DataflowConstProp.32bit.diff
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Expand Up @@ -13,7 +13,7 @@
StorageLive(_1);
- _1 = const 1_usize as std::boxed::Box<Never> (Transmute);
+ _1 = const Box::<Never>(Unique::<Never> {{ pointer: NonNull::<Never> {{ pointer: {0x1 as *const Never} }}, _marker: PhantomData::<Never> }}, std::alloc::Global);
_2 = copy (((_1.0: std::ptr::Unique<Never>).0: std::ptr::NonNull<Never>).0: *const Never);
_2 = copy ((_1.0: std::ptr::Unique<Never>).0: std::ptr::NonNull<Never>) as *const Never (Transmute);
unreachable;
}
}
Expand Down
2 changes: 1 addition & 1 deletion tests/mir-opt/dataflow-const-prop/transmute.unreachable_box.DataflowConstProp.64bit.diff
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Expand Up @@ -13,7 +13,7 @@
StorageLive(_1);
- _1 = const 1_usize as std::boxed::Box<Never> (Transmute);
+ _1 = const Box::<Never>(Unique::<Never> {{ pointer: NonNull::<Never> {{ pointer: {0x1 as *const Never} }}, _marker: PhantomData::<Never> }}, std::alloc::Global);
_2 = copy (((_1.0: std::ptr::Unique<Never>).0: std::ptr::NonNull<Never>).0: *const Never);
_2 = copy ((_1.0: std::ptr::Unique<Never>).0: std::ptr::NonNull<Never>) as *const Never (Transmute);
unreachable;
}
}
Expand Down
2 changes: 1 addition & 1 deletion tests/mir-opt/lower_intrinsics.transmute_to_box_uninhabited.LowerIntrinsics.panic-abort.diff
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Expand Up @@ -17,7 +17,7 @@
}

bb1: {
_2 = copy (((_1.0: std::ptr::Unique<Never>).0: std::ptr::NonNull<Never>).0: *const Never);
_2 = copy ((_1.0: std::ptr::Unique<Never>).0: std::ptr::NonNull<Never>) as *const Never (Transmute);
PlaceMention((*_2));
unreachable;
}
Expand Down
2 changes: 1 addition & 1 deletion ...s/mir-opt/lower_intrinsics.transmute_to_box_uninhabited.LowerIntrinsics.panic-unwind.diff
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Expand Up @@ -17,7 +17,7 @@
}

bb1: {
_2 = copy (((_1.0: std::ptr::Unique<Never>).0: std::ptr::NonNull<Never>).0: *const Never);
_2 = copy ((_1.0: std::ptr::Unique<Never>).0: std::ptr::NonNull<Never>) as *const Never (Transmute);
PlaceMention((*_2));
unreachable;
}
Expand Down
2 changes: 1 addition & 1 deletion tests/mir-opt/retag.box_to_raw_mut.SimplifyCfg-pre-optimizations.after.panic-abort.mir
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Expand Up @@ -9,7 +9,7 @@ fn box_to_raw_mut(_1: &mut Box<i32>) -> *mut i32 {
bb0: {
Retag([fn entry] _1);
_2 = deref_copy (*_1);
_3 = copy (((_2.0: std::ptr::Unique<i32>).0: std::ptr::NonNull<i32>).0: *const i32);
_3 = copy ((_2.0: std::ptr::Unique<i32>).0: std::ptr::NonNull<i32>) as *const i32 (Transmute);
_0 = &raw mut (*_3);
Retag([raw] _0);
return;
Expand Down
2 changes: 1 addition & 1 deletion tests/mir-opt/retag.box_to_raw_mut.SimplifyCfg-pre-optimizations.after.panic-unwind.mir
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Expand Up @@ -9,7 +9,7 @@ fn box_to_raw_mut(_1: &mut Box<i32>) -> *mut i32 {
bb0: {
Retag([fn entry] _1);
_2 = deref_copy (*_1);
_3 = copy (((_2.0: std::ptr::Unique<i32>).0: std::ptr::NonNull<i32>).0: *const i32);
_3 = copy ((_2.0: std::ptr::Unique<i32>).0: std::ptr::NonNull<i32>) as *const i32 (Transmute);
_0 = &raw mut (*_3);
Retag([raw] _0);
return;
Expand Down
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