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cleanup: handle -Zmutable-noalias like -Zbox-noalias

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This commit is contained in:
Erik Desjardins 2023-01-04 19:24:42 -05:00
parent c7572670a1
commit d165a6d708
4 changed files with 31 additions and 28 deletions
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19
compiler/rustc_ty_utils/src/abi.rs
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@ -256,6 +256,11 @@ fn adjust_for_rust_scalar<'tcx>(
// See https://github.com/rust-lang/unsafe-code-guidelines/issues/326
let noalias_for_box = cx.tcx.sess.opts.unstable_opts.box_noalias.unwrap_or(true);
// LLVM prior to version 12 had known miscompiles in the presence of noalias attributes
// (see #54878), so it was conditionally disabled, but we don't support earlier
// versions at all anymore. We still support turning it off using -Zmutable-noalias.
let noalias_mut_ref = cx.tcx.sess.opts.unstable_opts.mutable_noalias.unwrap_or(true);
// `&mut` pointer parameters never alias other parameters,
// or mutable global data
//
@ -263,15 +268,9 @@ fn adjust_for_rust_scalar<'tcx>(
// and can be marked as both `readonly` and `noalias`, as
// LLVM's definition of `noalias` is based solely on memory
// dependencies rather than pointer equality
//
// Due to past miscompiles in LLVM, we apply a separate NoAliasMutRef attribute
// for UniqueBorrowed arguments, so that the codegen backend can decide whether
// or not to actually emit the attribute. It can also be controlled with the
// `-Zmutable-noalias` debugging option.
let no_alias = match kind {
PointerKind::SharedMutable
| PointerKind::UniqueBorrowed
| PointerKind::UniqueBorrowedPinned => false,
PointerKind::SharedMutable | PointerKind::UniqueBorrowedPinned => false,
PointerKind::UniqueBorrowed => noalias_mut_ref,
PointerKind::UniqueOwned => noalias_for_box,
PointerKind::Frozen => true,
};
@ -284,10 +283,6 @@ fn adjust_for_rust_scalar<'tcx>(
if kind == PointerKind::Frozen && !is_return {
attrs.set(ArgAttribute::ReadOnly);
}
if kind == PointerKind::UniqueBorrowed && !is_return {
attrs.set(ArgAttribute::NoAliasMutRef);
}
}
}
}