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Work around llvm 12's memory ordering restrictions. #98385

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Jun 26, 2022
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Work around llvm 12's memory ordering restrictions. #98385

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16 changes: 15 additions & 1 deletion compiler/rustc_codegen_llvm/src/builder.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -1064,11 +1064,25 @@ impl<'a, 'll, 'tcx> BuilderMethods<'a, 'tcx> for Builder<'a, 'll, 'tcx> {
dst: &'ll Value,
cmp: &'ll Value,
src: &'ll Value,
order: rustc_codegen_ssa::common::AtomicOrdering,
mut order: rustc_codegen_ssa::common::AtomicOrdering,
failure_order: rustc_codegen_ssa::common::AtomicOrdering,
weak: bool,
) -> &'ll Value {
let weak = if weak { llvm::True } else { llvm::False };
if llvm_util::get_version() < (13, 0, 0) {
use rustc_codegen_ssa::common::AtomicOrdering::*;
// Older llvm has the pre-C++17 restriction on
// success and failure memory ordering,
// requiring the former to be at least as strong as the latter.
// So, for llvm 12, we upgrade the success ordering to a stronger
// one if necessary.
match (order, failure_order) {
(Relaxed, Acquire) => order = Acquire,
(Release, Acquire) => order = AcquireRelease,
(_, SequentiallyConsistent) => order = SequentiallyConsistent,
_ => {}
}
}
unsafe {
llvm::LLVMRustBuildAtomicCmpXchg(
self.llbuilder,
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