Auto merge of #98521 - JohnTitor:rollup-tl9sblx, r=JohnTitor

Rollup of 8 pull requests

Successful merges:

 - #98371 (Fix printing `impl trait` under binders)
 - #98385 (Work around llvm 12's memory ordering restrictions.)
 - #98474 (x.py: Support systems with only `python3` not `python`)
 - #98488 (Bump RLS to latest master on rust-lang/rls)
 - #98491 (Fix backtrace UI test when panic=abort is used)
 - #98502 (Fix source sidebar hover in ayu theme)
 - #98509 (diagnostics: consider parameter count when suggesting smart pointers)
 - #98513 (Fix LLVM rebuild with download-ci-llvm.)

Failed merges:

r? `@ghost`
`@rustbot` modify labels: rollup

1 files changed, 15 insertions, 1 deletions

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 @@ 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,