[llvm-branch-commits] [llvm][IR] Extend BranchWeightMetadata to track provenance of weights (PR #86609)

[Matthias Braun via llvm-branch-commits]

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@@ -106,6 +104,30 @@ bool hasValidBranchWeightMD(const Instruction &I) {
   return getValidBranchWeightMDNode(I);
 }
 
+bool hasExpectedProvenance(const Instruction &I) {
+  auto *ProfileData = I.getMetadata(LLVMContext::MD_prof);
+  return hasExpectedProvenance(ProfileData);
+}
+
+bool hasExpectedProvenance(const MDNode *ProfileData) {
+  if (!isBranchWeightMD(ProfileData))
+    return false;
+
+  auto *ProfDataName = dyn_cast<MDString>(ProfileData->getOperand(1));
+  if (!ProfDataName)
+    return false;
+  return ProfDataName->getString().equals("expected");
+}
+
+unsigned getBranchWeightOffset(const Instruction &I) {
+  auto *ProfileData = I.getMetadata(LLVMContext::MD_prof);
+  return getBranchWeightOffset(ProfileData);
+}
+
+unsigned getBranchWeightOffset(const MDNode *ProfileData) {
+  return hasExpectedProvenance(ProfileData) ? 2 : 1;
+}
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MatzeB wrote:

What about a `hasBranchWeightProvenance()` API instead that just checks whether there is a string? That way you would get the same effect today but can skip the string comparison (and maybe get better behavior if there is a string that isn't actually "expected")

https://github.com/llvm/llvm-project/pull/86609