[llvm] [llvm-profgen] Improve sample profile density (PR #92144)

[via llvm-commits]

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@@ -768,9 +747,88 @@ void ProfileGenerator::populateBoundarySamplesForAllFunctions(
   }
 }
 
+// Note that ideally the size should be the number of function instruction.
+// However, for probe-based profile, we don't have the accurate instruction
+// count for each probe, instead, the probe sample is the samples count for the
+// block, which is equivelant to total_instruction_samples/num_of_instruction in
+// one block. Hence, we use the number of probe as a proxy for the function's
+// size.
+void ProfileGeneratorBase::calculateBodySamplesAndSize(
+    const FunctionSamples &FSamples, uint64_t &TotalBodySamples,
+    uint64_t &FuncBodySize) {
+  FuncBodySize +=
+      FSamples.getBodySamples().size() + FSamples.getCallsiteSamples().size();
+
+  for (const auto &I : FSamples.getBodySamples())
+    TotalBodySamples += I.second.getSamples();
+
+  // The whole function could be inlined and optimized out, use the callsite
+  // head samples instead to estimate the body count.
+  for (const auto &CallsiteSamples : FSamples.getCallsiteSamples())
+    for (const auto &Callee : CallsiteSamples.second) {
+      // This is used for caluculating the binary-level density, so the
+      // inlinees' samples and size should be included in the calculation.
+      calculateBodySamplesAndSize(Callee.second, TotalBodySamples,
+                                  FuncBodySize);
+      TotalBodySamples += Callee.second.getHeadSamplesEstimate();
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WenleiHe wrote:

Is this needed? It seems to duplicate the inlinee's body samples. Can we remove?

https://github.com/llvm/llvm-project/pull/92144