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

[Simon Pilgrim via llvm-commits]

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@@ -882,7 +886,8 @@ def ProcessorFeatures {
   list<SubtargetFeature> NHMTuning = [TuningMacroFusion,
                                       TuningSlowDivide64,
                                       TuningInsertVZEROUPPER,
-                                      TuningNoDomainDelayMov];
+                                      TuningNoDomainDelayMov,
+                                      TuningAvoidMFENCE];
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RKSimon wrote:

Probably add TuningAvoidMFENCE to tuning for x86-64-v2 and later?

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