bjoernager/rust
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Enable mutable noalias by default for LLVM 12

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We don't have any known noalias bugs for LLVM 12 ... yet.
This commit is contained in:
Nikita Popov 2021-03-18 22:50:58 +01:00
parent c3f9403f59
commit 39ed64399e
3 changed files with 14 additions and 16 deletions
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22
compiler/rustc_codegen_llvm/src/abi.rs
View file

@ -1,6 +1,7 @@
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;
@ -51,18 +52,15 @@ pub trait ArgAttributesExt {
}
fn should_use_mutable_noalias(cx: &CodegenCx<'_, '_>) -> bool {
// Previously we would only emit noalias annotations for LLVM >= 6 or in
// panic=abort mode. That was deemed right, as prior versions had many bugs
// in conjunction with unwinding, but later versions didn’t seem to have
// said issues. See issue #31681.
//
// Alas, later on we encountered a case where noalias would generate wrong
// code altogether even with recent versions of LLVM in *safe* code with no
// unwinding involved. See #54462.
//
// For now, do not enable mutable_noalias by default at all, while the
// issue is being figured out.
cx.tcx.sess.opts.debugging_opts.mutable_noalias.unwrap_or(false)
// 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))
}
impl ArgAttributesExt for ArgAttributes {

2
compiler/rustc_session/src/options.rs
View file

@ -998,7 +998,7 @@ options! {DebuggingOptions, DebuggingSetter, basic_debugging_options,
mir_opt_level: Option<usize> = (None, parse_opt_uint, [TRACKED],
"MIR optimization level (0-4; default: 1 in non optimized builds and 2 in optimized builds)"),
mutable_noalias: Option<bool> = (None, parse_opt_bool, [TRACKED],
"emit noalias metadata for mutable references (default: no)"),
"emit noalias metadata for mutable references (default: yes for LLVM >= 12, otherwise no)"),
new_llvm_pass_manager: bool = (false, parse_bool, [TRACKED],
"use new LLVM pass manager (default: no)"),
nll_facts: bool = (false, parse_bool, [UNTRACKED],

6
src/test/codegen/function-arguments.rs
View file

@ -43,13 +43,13 @@ pub fn named_borrow<'r>(_: &'r i32) {
pub fn unsafe_borrow(_: &UnsafeInner) {
}
// CHECK: @mutable_unsafe_borrow(i16* align 2 dereferenceable(2) %_1)
// CHECK: @mutable_unsafe_borrow(i16* noalias 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* align 4 dereferenceable(4) %_1)
// CHECK: @mutable_borrow(i32* noalias 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]* nonnull align 1 %_1.0, [[USIZE]] %_1.1)
// CHECK: @mutable_slice([0 x i8]* noalias nonnull align 1 %_1.0, [[USIZE]] %_1.1)
// FIXME #25759 This should also have `nocapture`
#[no_mangle]
pub fn mutable_slice(_: &mut [u8]) {