[llvm] [X86] Use fence(seq_cst) in IdempotentRMWIntoFencedLoad (PR #126521)

[Phoebe Wang via llvm-commits]

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@@ -31807,21 +31807,10 @@ X86TargetLowering::lowerIdempotentRMWIntoFencedLoad(AtomicRMWInst *AI) const {
   // otherwise, we might be able to be more aggressive on relaxed idempotent
   // rmw. In practice, they do not look useful, so we don't try to be
   // especially clever.
-  if (SSID == SyncScope::SingleThread)
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phoebewang wrote:

Do we have test case to cover this condition?

https://github.com/llvm/llvm-project/pull/126521