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

[via llvm-commits]

================
@@ -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();
+      FuncBodySize++;
+    }
+    // The whole function could be inlined and optimized out, use the callsite
+    // head samples instead to estimate the body count.
+    if (FuncBodySize == 0) {
----------------
WenleiHe wrote:

Why do we *only* include inlinees when the function body itself is fully optimized away? This seems inconsistent. 

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