[NFC][Sample PGO] Avoid non-const accessor for CallsiteSamples

[wenlei]

Summary

Exposing a non-const accessor for clearing CallsiteSamples during flattening is a big of an overkill. Replace the non-const accessor with removeAllCallsiteSamples.

[wlei]

Good catch!

[marksantaniello]

llvm/include/llvm/ProfileData/SampleProf.h

806

Consider "the swap trick" to guarantee that we free the memory?

CallsiteSamplesMap EmptyCallsiteSamples;
std::swap(CallsiteSamples, EmptyCallsiteSamples);

[wenlei]

llvm/include/llvm/ProfileData/SampleProf.h

806

It's a std::map, so clear should be sufficient.

llvm/include/llvm/ProfileData/SampleProf.h

if (I != BodySamples.end()) {
       Count = I->second.removeCalledTarget(FName);
       Count = I->second.removeSamples(Count);
       if (!I->second.getSamples())
         BodySamples.erase(I);
     }
     return Count;
   }
 
+  // Remove all call site samples for inlinees. This is needed when flattening
+  // a nested profile.
+  void removeAllCallsiteSamples() {
+    CallsiteSamples.clear();
+  }
+
   // Accumulate all call target samples to update the body samples.
   void updateCallsiteSamples() {
     for (auto &I : BodySamples) {
       uint64_t TargetSamples = I.second.getCallTargetSum();
       // It's possible that the body sample count can be greater than the call
       // target sum. E.g, if some call targets are external targets, they won't
       // be considered valid call targets, but the body sample count which is
       // from lbr ranges can actually include them.
public:
   /// Return all the samples collected in the body of the function.
   const BodySampleMap &getBodySamples() const { return BodySamples; }
 
   /// Return all the callsite samples collected in the body of the function.
   const CallsiteSampleMap &getCallsiteSamples() const {
     return CallsiteSamples;
   }
 
-  CallsiteSampleMap &getCallsiteSamples() { return CallsiteSamples; }
-
   /// Return the maximum of sample counts in a function body. When SkipCallSite
   /// is false, which is the default, the return count includes samples in the
   /// inlined functions. When SkipCallSite is true, the return count only
   /// considers the body samples.
   uint64_t getMaxCountInside(bool SkipCallSite = false) const {
     uint64_t MaxCount = 0;
     for (const auto &L : getBodySamples())
       MaxCount = std::max(MaxCount, L.second.getSamples());
private:
   static void flattenNestedProfile(SampleProfileMap &OutputProfiles,
                                    const FunctionSamples &FS) {
     // To retain the context, checksum, attributes of the original profile, make
     // a copy of it if no profile is found.
     SampleContext &Context = FS.getContext();
     auto Ret = OutputProfiles.try_emplace(Context, FS);
     FunctionSamples &Profile = Ret.first->second;
     if (Ret.second) {
-      // When it's the copy of the old profile, just clear all the inlinees'
-      // samples.
-      Profile.getCallsiteSamples().clear();
+      // Clear nested inlinees' samples for the flattened copy. These inlinees
+      // will have their own top-level entries after flattening.
+      Profile.removeAllCallsiteSamples();
       // We recompute TotalSamples later, so here set to zero.
       Profile.setTotalSamples(0);
     } else {
       for (const auto &[LineLocation, SampleRecord] : FS.getBodySamples()) {
         Profile.addSampleRecord(LineLocation, SampleRecord);
       }
     }