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Tell LLVM about read-only captures

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`&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.
This commit is contained in:
Nikita Popov
2025-08-11 17:18:23 +02:00
parent 8365fcb2b8
commit d71ed8d19b
10 changed files with 48 additions and 14 deletions
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7
compiler/rustc_codegen_llvm/src/abi.rs
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@@ -42,12 +42,13 @@ trait ArgAttributesExt {
const ABI_AFFECTING_ATTRIBUTES: [(ArgAttribute, llvm::AttributeKind); 1] =
[(ArgAttribute::InReg, llvm::AttributeKind::InReg)];
const OPTIMIZATION_ATTRIBUTES: [(ArgAttribute, llvm::AttributeKind); 5] = [
const OPTIMIZATION_ATTRIBUTES: [(ArgAttribute, llvm::AttributeKind); 6] = [
(ArgAttribute::NoAlias, llvm::AttributeKind::NoAlias),
(ArgAttribute::NoCapture, llvm::AttributeKind::NoCapture),
(ArgAttribute::NonNull, llvm::AttributeKind::NonNull),
(ArgAttribute::ReadOnly, llvm::AttributeKind::ReadOnly),
(ArgAttribute::NoUndef, llvm::AttributeKind::NoUndef),
(ArgAttribute::CapturesReadOnly, llvm::AttributeKind::CapturesReadOnly),
];
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<[&'
}
for (attr, llattr) in OPTIMIZATION_ATTRIBUTES {
if regular.contains(attr) {
// captures(address, read_provenance) is only available since LLVM 21.
if attr == ArgAttribute::CapturesReadOnly && llvm_util::get_version() < (21, 0, 0) {
continue;
}
attrs.push(llattr.create_attr(cx.llcx));
}
}