[llvm] [llvm-profgen] Fix bogus trace check (PR #225569)

[Amir Ayupov via llvm-commits]

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@@ -911,6 +919,19 @@ void HybridPerfReader::parseSample(TraceStream &TraceIt, uint64_t Count) {
       if (IgnoreStackSamples) {
         Sample->CallStack.clear();
       } else {
+        NumTotalHybridSample++;
+        // Drop samples whose callchain and LBR disagree before the
+        // canonicalization below hides the disagreement.
+        uint64_t StackLeaf = Sample->CallStack.front();
+        uint64_t LBRLeaf = Sample->LBRStack[0].Target;
+        if (!isValidTrace(Binary, StackLeaf, LBRLeaf)) {
+          NumBogusTrace++;
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aaupov wrote:

I don't think we need to distinguish hot/cold code if the number of bogus samples is small, as it should be, e.g. <1-2%.

If the profile has high skid pctage, I think it's best to just warn that the profile may not be accurate enough for optimization.

https://github.com/llvm/llvm-project/pull/225569