From 903357604d154888320135086e4d862bc71d644a Mon Sep 17 00:00:00 2001 From: Mara Bos Date: Wed, 22 Jun 2022 14:48:49 +0200 Subject: [PATCH] Work around llvm 12's memory ordering restrictions. 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, this upgrades the success ordering to a stronger one if necessary. --- compiler/rustc_codegen_llvm/src/builder.rs | 16 +++++++++++++++- 1 file changed, 15 insertions(+), 1 deletion(-) diff --git a/compiler/rustc_codegen_llvm/src/builder.rs b/compiler/rustc_codegen_llvm/src/builder.rs index c41a41980eb..8c1e865762c 100644 --- a/compiler/rustc_codegen_llvm/src/builder.rs +++ b/compiler/rustc_codegen_llvm/src/builder.rs @@ -1064,11 +1064,25 @@ fn atomic_cmpxchg( 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,