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

[via llvm-commits]

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@@ -1032,6 +1035,78 @@ void CSProfileGenerator::convertToProfileMap() {
   IsProfileValidOnTrie = false;
 }
 
+void CSProfileGenerator::calculateAndShowDensity(
+    SampleContextTracker &CTracker) {
+  double Density = calculateDensity(CTracker);
+  showDensitySuggestion(Density, ProfileDensityHotFuncCutOff);
+}
+
+// Calculate Profile-density:
+// Sort the list of function-density in descending order and iterate them once
+// their accumulated total samples exceeds the percentage_threshold of total
+// profile samples, the profile-density is the last(minimum) function-density of
+// the processed functions, which means all the functions significant to perf
+// are on good density if the profile-density is good, or in other words, if the
+// profile-density is bad, the accumulated samples for all the bad density
+// profile exceeds the (100% - percentage_threshold).
+// The percentage_threshold(--profile-density-hot-func-cutoff) is configurable
+// depending on how much regression the system want to tolerate.
+double CSProfileGenerator::calculateDensity(SampleContextTracker &CTracker) {
+  double ProfileDensity = 0.0;
+
+  uint64_t TotalProfileSamples = 0;
+  // A list of the function profile density and total samples.
+  std::vector<std::pair<double, uint64_t>> DensityList;
+  for (const auto *Node : CTracker) {
+    const auto *FSamples = Node->getFunctionSamples();
+    if (!FSamples)
+      continue;
+
+    uint64_t TotalBodySamples = 0;
+    uint64_t FuncBodySize = 0;
+    for (const auto &I : FSamples->getBodySamples()) {
+      TotalBodySamples += I.second.getSamples();
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WenleiHe wrote:

I guess the question is why do we want to exclude inlinees? we can count total samples including inlinees, and also size including inliness. Otherwise we don't cover such inlinees in density metrics -- what if inlinee has a low density problem? 

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