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Tell LLVM about read-only captures
`&Freeze` parameters are not only `readonly` within the function, but any captures of the pointer can also only be used for reads. This can now be encoded using the `captures(address, read_provenance)` attribute.
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12 files changed

+36
-20
lines changed

12 files changed

+36
-20
lines changed

‎compiler/rustc_codegen_llvm/src/abi.rs

Lines changed: 6 additions & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -42,12 +42,13 @@ trait ArgAttributesExt {
4242
const ABI_AFFECTING_ATTRIBUTES: [(ArgAttribute, llvm::AttributeKind); 1] =
4343
[(ArgAttribute::InReg, llvm::AttributeKind::InReg)];
4444

45-
const OPTIMIZATION_ATTRIBUTES: [(ArgAttribute, llvm::AttributeKind); 5] = [
45+
const OPTIMIZATION_ATTRIBUTES: [(ArgAttribute, llvm::AttributeKind); 6] = [
4646
(ArgAttribute::NoAlias, llvm::AttributeKind::NoAlias),
4747
(ArgAttribute::NoCapture, llvm::AttributeKind::NoCapture),
4848
(ArgAttribute::NonNull, llvm::AttributeKind::NonNull),
4949
(ArgAttribute::ReadOnly, llvm::AttributeKind::ReadOnly),
5050
(ArgAttribute::NoUndef, llvm::AttributeKind::NoUndef),
51+
(ArgAttribute::CapturesReadOnly, llvm::AttributeKind::CapturesReadOnly),
5152
];
5253

5354
fn get_attrs<'ll>(this: &ArgAttributes, cx: &CodegenCx<'ll, '_>) -> SmallVec<[&'ll Attribute; 8]> {
@@ -83,6 +84,10 @@ fn get_attrs<'ll>(this: &ArgAttributes, cx: &CodegenCx<'ll, '_>) -> SmallVec<[&'
8384
}
8485
for (attr, llattr) in OPTIMIZATION_ATTRIBUTES {
8586
if regular.contains(attr) {
87+
// captures(address, read_provenance) is only available since LLVM 21.
88+
if attr == ArgAttribute::CapturesReadOnly && llvm_util::get_version() < (21, 0, 0) {
89+
continue;
90+
}
8691
attrs.push(llattr.create_attr(cx.llcx));
8792
}
8893
}

‎compiler/rustc_codegen_llvm/src/llvm/ffi.rs

Lines changed: 1 addition & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -250,6 +250,7 @@ pub(crate) enum AttributeKind {
250250
Writable = 42,
251251
DeadOnUnwind = 43,
252252
DeadOnReturn = 44,
253+
CapturesReadOnly = 45,
253254
}
254255

255256
/// LLVMIntPredicate

‎compiler/rustc_llvm/llvm-wrapper/RustWrapper.cpp

Lines changed: 8 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -278,6 +278,7 @@ enum class LLVMRustAttributeKind {
278278
Writable = 42,
279279
DeadOnUnwind = 43,
280280
DeadOnReturn = 44,
281+
CapturesReadOnly = 45,
281282
};
282283

283284
static Attribute::AttrKind fromRust(LLVMRustAttributeKind Kind) {
@@ -376,6 +377,8 @@ static Attribute::AttrKind fromRust(LLVMRustAttributeKind Kind) {
376377
#else
377378
report_fatal_error("DeadOnReturn attribute requires LLVM 21 or later");
378379
#endif
380+
case LLVMRustAttributeKind::CapturesReadOnly:
381+
report_fatal_error("Should be handled separately");
379382
}
380383
report_fatal_error("bad LLVMRustAttributeKind");
381384
}
@@ -430,6 +433,11 @@ LLVMRustCreateAttrNoValue(LLVMContextRef C, LLVMRustAttributeKind RustAttr) {
430433
if (RustAttr == LLVMRustAttributeKind::NoCapture) {
431434
return wrap(Attribute::getWithCaptureInfo(*unwrap(C), CaptureInfo::none()));
432435
}
436+
if (RustAttr == LLVMRustAttributeKind::CapturesReadOnly) {
437+
return wrap(Attribute::getWithCaptureInfo(*unwrap(C),
438+
CaptureInfo(CaptureComponents::Address |
439+
CaptureComponents::ReadProvenance)));
440+
}
433441
#endif
434442
return wrap(Attribute::get(*unwrap(C), fromRust(RustAttr)));
435443
}

‎compiler/rustc_target/src/callconv/mod.rs

Lines changed: 1 addition & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -119,6 +119,7 @@ mod attr_impl {
119119
const ReadOnly = 1 << 4;
120120
const InReg = 1 << 5;
121121
const NoUndef = 1 << 6;
122+
const CapturesReadOnly = 1 << 7;
122123
}
123124
}
124125
rustc_data_structures::external_bitflags_debug! { ArgAttribute }

‎compiler/rustc_ty_utils/src/abi.rs

Lines changed: 1 addition & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -355,6 +355,7 @@ fn adjust_for_rust_scalar<'tcx>(
355355

356356
if matches!(kind, PointerKind::SharedRef { frozen: true }) && !is_return {
357357
attrs.set(ArgAttribute::ReadOnly);
358+
attrs.set(ArgAttribute::CapturesReadOnly);
358359
}
359360
}
360361
}

‎tests/codegen-llvm/function-arguments.rs

Lines changed: 10 additions & 10 deletions
Original file line numberDiff line numberDiff line change
@@ -80,7 +80,7 @@ pub fn option_nonzero_int(x: Option<NonZero<u64>>) -> Option<NonZero<u64>> {
8080
x
8181
}
8282

83-
// CHECK: @readonly_borrow(ptr noalias noundef readonly align 4 dereferenceable(4) %_1)
83+
// CHECK: @readonly_borrow(ptr noalias noundef readonly align 4{{( captures\(address, read_provenance\))}} dereferenceable(4) %_1)
8484
// FIXME #25759 This should also have `nocapture`
8585
#[no_mangle]
8686
pub fn readonly_borrow(_: &i32) {}
@@ -91,12 +91,12 @@ pub fn readonly_borrow_ret() -> &'static i32 {
9191
loop {}
9292
}
9393

94-
// CHECK: @static_borrow(ptr noalias noundef readonly align 4 dereferenceable(4) %_1)
94+
// CHECK: @static_borrow(ptr noalias noundef readonly align 4{{( captures\(address, read_provenance\))}} dereferenceable(4) %_1)
9595
// static borrow may be captured
9696
#[no_mangle]
9797
pub fn static_borrow(_: &'static i32) {}
9898

99-
// CHECK: @named_borrow(ptr noalias noundef readonly align 4 dereferenceable(4) %_1)
99+
// CHECK: @named_borrow(ptr noalias noundef readonly align 4{{( captures\(address, read_provenance\))}} dereferenceable(4) %_1)
100100
// borrow with named lifetime may be captured
101101
#[no_mangle]
102102
pub fn named_borrow<'r>(_: &'r i32) {}
@@ -129,7 +129,7 @@ pub fn mutable_borrow_ret() -> &'static mut i32 {
129129
// <https://github.com/rust-lang/unsafe-code-guidelines/issues/381>.
130130
pub fn mutable_notunpin_borrow(_: &mut NotUnpin) {}
131131

132-
// CHECK: @notunpin_borrow(ptr noalias noundef readonly align 4 dereferenceable(4) %_1)
132+
// CHECK: @notunpin_borrow(ptr noalias noundef readonly align 4{{( captures\(address, read_provenance\))}} dereferenceable(4) %_1)
133133
// But `&NotUnpin` behaves perfectly normal.
134134
#[no_mangle]
135135
pub fn notunpin_borrow(_: &NotUnpin) {}
@@ -138,12 +138,12 @@ pub fn notunpin_borrow(_: &NotUnpin) {}
138138
#[no_mangle]
139139
pub fn indirect_struct(_: S) {}
140140

141-
// CHECK: @borrowed_struct(ptr noalias noundef readonly align 4 dereferenceable(32) %_1)
141+
// CHECK: @borrowed_struct(ptr noalias noundef readonly align 4{{( captures\(address, read_provenance\))}} dereferenceable(32) %_1)
142142
// FIXME #25759 This should also have `nocapture`
143143
#[no_mangle]
144144
pub fn borrowed_struct(_: &S) {}
145145

146-
// CHECK: @option_borrow(ptr noalias noundef readonly align 4 dereferenceable_or_null(4) %_x)
146+
// CHECK: @option_borrow(ptr noalias noundef readonly align 4{{( captures\(address, read_provenance\))}} dereferenceable_or_null(4) %_x)
147147
#[no_mangle]
148148
pub fn option_borrow(_x: Option<&i32>) {}
149149

@@ -185,7 +185,7 @@ pub fn _box(x: Box<i32>) -> Box<i32> {
185185
// With a custom allocator, it should *not* have `noalias`. (See
186186
// <https://github.com/rust-lang/miri/issues/3341> for why.) The second argument is the allocator,
187187
// which is a reference here that still carries `noalias` as usual.
188-
// CHECK: @_box_custom(ptr noundef nonnull align 4 %x.0, ptr noalias noundef nonnull readonly align 1 %x.1)
188+
// CHECK: @_box_custom(ptr noundef nonnull align 4 %x.0, ptr noalias noundef nonnull readonly align 1{{( captures\(address, read_provenance\))}} %x.1)
189189
#[no_mangle]
190190
pub fn _box_custom(x: Box<i32, &std::alloc::Global>) {
191191
drop(x)
@@ -208,7 +208,7 @@ pub fn struct_return() -> S {
208208
#[no_mangle]
209209
pub fn helper(_: usize) {}
210210

211-
// CHECK: @slice(ptr noalias noundef nonnull readonly align 1 %_1.0, [[USIZE]] noundef %_1.1)
211+
// CHECK: @slice(ptr noalias noundef nonnull readonly align 1{{( captures\(address, read_provenance\))}} %_1.0, [[USIZE]] noundef %_1.1)
212212
// FIXME #25759 This should also have `nocapture`
213213
#[no_mangle]
214214
pub fn slice(_: &[u8]) {}
@@ -227,7 +227,7 @@ pub fn unsafe_slice(_: &[UnsafeInner]) {}
227227
#[no_mangle]
228228
pub fn raw_slice(_: *const [u8]) {}
229229

230-
// CHECK: @str(ptr noalias noundef nonnull readonly align 1 %_1.0, [[USIZE]] noundef %_1.1)
230+
// CHECK: @str(ptr noalias noundef nonnull readonly align 1{{( captures\(address, read_provenance\))}} %_1.0, [[USIZE]] noundef %_1.1)
231231
// FIXME #25759 This should also have `nocapture`
232232
#[no_mangle]
233233
pub fn str(_: &[u8]) {}
@@ -259,7 +259,7 @@ pub fn trait_option(x: Option<Box<dyn Drop + Unpin>>) -> Option<Box<dyn Drop + U
259259
x
260260
}
261261

262-
// CHECK: { ptr, [[USIZE]] } @return_slice(ptr noalias noundef nonnull readonly align 2 %x.0, [[USIZE]] noundef %x.1)
262+
// CHECK: { ptr, [[USIZE]] } @return_slice(ptr noalias noundef nonnull readonly align 2{{( captures\(address, read_provenance\))}} %x.0, [[USIZE]] noundef %x.1)
263263
#[no_mangle]
264264
pub fn return_slice(x: &[u16]) -> &[u16] {
265265
x

‎tests/codegen-llvm/range-attribute.rs

Lines changed: 1 addition & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -67,7 +67,7 @@ pub fn enum2_value(x: Enum2) -> Enum2 {
6767
x
6868
}
6969

70-
// CHECK: noundef [[USIZE]] @takes_slice(ptr noalias noundef nonnull readonly align 4 %x.0, [[USIZE]] noundef %x.1)
70+
// CHECK: noundef [[USIZE]] @takes_slice(ptr {{.*}} %x.0, [[USIZE]] noundef %x.1)
7171
#[no_mangle]
7272
pub fn takes_slice(x: &[i32]) -> usize {
7373
x.len()

‎tests/ui/abi/debug.generic.stderr

Lines changed: 1 addition & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -939,7 +939,7 @@ error: fn_abi_of(assoc_test) = FnAbi {
939939
},
940940
mode: Direct(
941941
ArgAttributes {
942-
regular: NoAlias | NonNull | ReadOnly | NoUndef,
942+
regular: NoAlias | NonNull | ReadOnly | NoUndef | CapturesReadOnly,
943943
arg_ext: None,
944944
pointee_size: Size(2 bytes),
945945
pointee_align: Some(

‎tests/ui/abi/debug.riscv64.stderr

Lines changed: 1 addition & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -939,7 +939,7 @@ error: fn_abi_of(assoc_test) = FnAbi {
939939
},
940940
mode: Direct(
941941
ArgAttributes {
942-
regular: NoAlias | NonNull | ReadOnly | NoUndef,
942+
regular: NoAlias | NonNull | ReadOnly | NoUndef | CapturesReadOnly,
943943
arg_ext: None,
944944
pointee_size: Size(2 bytes),
945945
pointee_align: Some(

‎tests/ui/codegen/equal-pointers-unequal/as-cast/segfault.rs

Lines changed: 2 additions & 2 deletions
Original file line numberDiff line numberDiff line change
@@ -1,7 +1,7 @@
1-
//@ known-bug: #107975
21
//@ compile-flags: -Copt-level=2
3-
//@ run-pass
2+
//@ run-fail
43
//@ ignore-backends: gcc
4+
//@ min-llvm-version: 21
55

66
// https://github.com/rust-lang/rust/issues/107975#issuecomment-1431758601
77

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