[clang] [llvm] Support branch hint (PR #97721)

[Simon Pilgrim via cfe-commits]

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@@ -749,6 +749,11 @@ def TuningUseGLMDivSqrtCosts
     : SubtargetFeature<"use-glm-div-sqrt-costs", "UseGLMDivSqrtCosts", "true",
         "Use Goldmont specific floating point div/sqrt costs">;
 
+// Starting with Redwood Cove architecture, the branch has branch taken hint
+// (i.e., instruction prefix 3EH).
+def TuningBranchHint: SubtargetFeature<"branch-hint", "HasBranchHint", "true",
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RKSimon wrote:

Why have you added this as a Tuning bit and not a Feature bit? Tuning bits are guaranteed to work on all applicable CPUs - they just might not be performant. 

https://github.com/llvm/llvm-project/pull/97721