[CSSPGO] Fix redundant reading of profile metadata (#129609)

Fix a build speed regression due to repeated reading of profile
metadata. Before the function `readFuncMetadata(ProfileHasAttribute,
Profiles)` reads the metadata for all the functions(`Profiles`),
however, it's actually used for on-demand loading, it can be called for
multiple times, which leads to redundant reading that causes the build
speed regression. Now fix it to read the metadata only for the new
loaded functions(functions in the `FuncsToUse`).

Author: wlei-llvm

llvm/include/llvm/ProfileData/SampleProfReader.h

@@ -777,7 +777,7 @@ class SampleProfileReaderExtBinaryBase : public SampleProfileReaderBinary {
   std::error_code readSecHdrTable();
 
   std::error_code readFuncMetadata(bool ProfileHasAttribute,
-                                   SampleProfileMap &Profiles);
+                                   DenseSet<FunctionSamples *> &Profiles);
   std::error_code readFuncMetadata(bool ProfileHasAttribute);
   std::error_code readFuncMetadata(bool ProfileHasAttribute,
                                    FunctionSamples *FProfile);

llvm/lib/ProfileData/SampleProfReader.cpp

@@ -826,13 +826,23 @@ bool SampleProfileReaderExtBinaryBase::useFuncOffsetList() const {
 std::error_code
 SampleProfileReaderExtBinaryBase::read(const DenseSet<StringRef> &FuncsToUse,
                                        SampleProfileMap &Profiles) {
+  if (FuncsToUse.empty())
+    return sampleprof_error::success;
+
   Data = ProfileSecRange.first;
   End = ProfileSecRange.second;
   if (std::error_code EC = readFuncProfiles(FuncsToUse, Profiles))
     return EC;
   End = Data;
+  DenseSet<FunctionSamples *> ProfilesToReadMetadata;
+  for (auto FName : FuncsToUse) {
+    auto I = Profiles.find(FName);
+    if (I != Profiles.end())
+      ProfilesToReadMetadata.insert(&I->second);
+  }
 
-  if (std::error_code EC = readFuncMetadata(ProfileHasAttribute, Profiles))
+  if (std::error_code EC =
+          readFuncMetadata(ProfileHasAttribute, ProfilesToReadMetadata))
     return EC;
   return sampleprof_error::success;
 }
@@ -1300,14 +1310,12 @@ SampleProfileReaderExtBinaryBase::readFuncMetadata(bool ProfileHasAttribute,
   return sampleprof_error::success;
 }
 
-std::error_code
-SampleProfileReaderExtBinaryBase::readFuncMetadata(bool ProfileHasAttribute,
-                                                   SampleProfileMap &Profiles) {
+std::error_code SampleProfileReaderExtBinaryBase::readFuncMetadata(
+    bool ProfileHasAttribute, DenseSet<FunctionSamples *> &Profiles) {
   if (FuncMetadataIndex.empty())
     return sampleprof_error::success;
 
-  for (auto &I : Profiles) {
-    FunctionSamples *FProfile = &I.second;
+  for (auto *FProfile : Profiles) {
     auto R = FuncMetadataIndex.find(FProfile->getContext().getHashCode());
     if (R == FuncMetadataIndex.end())
       continue;