[llvm] [X86] Prefer `lock or` over mfence (PR #106555)

[Simon Pilgrim via llvm-commits]

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@@ -1429,7 +1444,8 @@ def ProcessorFeatures {
                                          TuningFastScalarShiftMasks,
                                          TuningBranchFusion,
                                          TuningSBBDepBreaking,
-                                         TuningInsertVZEROUPPER];
+                                         TuningInsertVZEROUPPER,
+                                         TuningAvoidMFENCE];
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RKSimon wrote:

Please can you add TuningAvoidMFENCE to BtVer2Tuning as well?

https://github.com/llvm/llvm-project/pull/106555