Auto merge of rust-lang#86036 - nikic:disable-mutable-noalias, r=Mark-Simulacrum

[beta] Disable mutable noalias for Rust 1.53

Disable mutable noalias for the upcoming release to give this change more time to bake. I believe that was the consensus, and I wanted to make sure we don't forget :)

r? `@Mark-Simulacrum`

Author: bors

compiler/rustc_codegen_llvm/src/abi.rs

@@ -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;
@@ -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 {

src/test/codegen/function-arguments.rs

@@ -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) {
@@ -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]) {