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[beta] Disable mutable noalias for Rust 1.53 #86036

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Jun 9, 2021
Merged

[beta] Disable mutable noalias for Rust 1.53 #86036

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13 changes: 3 additions & 10 deletions compiler/rustc_codegen_llvm/src/abi.rs
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Original file line number Diff line number Diff line change
@@ -1,7 +1,6 @@
use crate::builder::Builder;
use crate::context::CodegenCx;
use crate::llvm::{self, AttributePlace};
use crate::llvm_util;
use crate::type_::Type;
use crate::type_of::LayoutLlvmExt;
use crate::value::Value;
Expand Down Expand Up @@ -52,15 +51,9 @@ pub trait ArgAttributesExt {
}

fn should_use_mutable_noalias(cx: &CodegenCx<'_, '_>) -> bool {
// LLVM prior to version 12 has known miscompiles in the presence of
// noalias attributes (see #54878). Only enable mutable noalias by
// default for versions we believe to be safe.
cx.tcx
.sess
.opts
.debugging_opts
.mutable_noalias
.unwrap_or_else(|| llvm_util::get_version() >= (12, 0, 0))
// While #84958 has been fixed, mutable noalias is not enabled by default
// in Rust 1.53 out of an abundance of caution.
cx.tcx.sess.opts.debugging_opts.mutable_noalias.unwrap_or(false)
}

impl ArgAttributesExt for ArgAttributes {
Expand Down
6 changes: 3 additions & 3 deletions src/test/codegen/function-arguments.rs
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Expand Up @@ -43,13 +43,13 @@ pub fn named_borrow<'r>(_: &'r i32) {
pub fn unsafe_borrow(_: &UnsafeInner) {
}

// CHECK: @mutable_unsafe_borrow(i16* noalias align 2 dereferenceable(2) %_1)
// CHECK: @mutable_unsafe_borrow(i16* align 2 dereferenceable(2) %_1)
// ... unless this is a mutable borrow, those never alias
#[no_mangle]
pub fn mutable_unsafe_borrow(_: &mut UnsafeInner) {
}

// CHECK: @mutable_borrow(i32* noalias align 4 dereferenceable(4) %_1)
// CHECK: @mutable_borrow(i32* align 4 dereferenceable(4) %_1)
// FIXME #25759 This should also have `nocapture`
#[no_mangle]
pub fn mutable_borrow(_: &mut i32) {
Expand Down Expand Up @@ -94,7 +94,7 @@ pub fn helper(_: usize) {
pub fn slice(_: &[u8]) {
}

// CHECK: @mutable_slice([0 x i8]* noalias nonnull align 1 %_1.0, [[USIZE]] %_1.1)
// CHECK: @mutable_slice([0 x i8]* nonnull align 1 %_1.0, [[USIZE]] %_1.1)
// FIXME #25759 This should also have `nocapture`
#[no_mangle]
pub fn mutable_slice(_: &mut [u8]) {
Expand Down