[llvm-profdata] Drop profile symbol list during merging AutoFDO profiles.

[hoy]

Summary

Adding a switch to drop profile symbol list during merging AutoFDO profiles. This is needed to minimize the impact on default profiles when the profile symbol list is enabled for the source input profiles. The symbol list is quite large and could potentially slow down the compiler.

[wenlei]

llvm/tools/llvm-profdata/llvm-profdata.cpp

1235

Add (only meaningful for -sample) to the description.

[hoy]

Addressing feedbacks.

[davidxl]

lgtm

llvm/test/tools/llvm-profdata/profile-symbol-list.test

 ; RUN: llvm-profdata merge -sample -extbinary -prof-sym-list=%S/Inputs/profile-symbol-list-1.text %S/Inputs/sample-profile.proftext -o %t.1.output
 ; RUN: llvm-profdata merge -sample -extbinary -prof-sym-list=%S/Inputs/profile-symbol-list-2.text %S/Inputs/sample-profile.proftext -o %t.2.output
 ; RUN: llvm-profdata merge -sample -extbinary %t.1.output %t.2.output -o %t.3.output
 ; RUN: llvm-profdata show -sample -show-prof-sym-list %t.3.output > %t.4.output
 ; RUN: diff -b %S/Inputs/profile-symbol-list.expected %t.4.output
+; RUN: llvm-profdata merge -sample -extbinary --drop-profile-symbol-list %t.1.output %t.2.output -o %t.5.output
+; RUN: llvm-profdata show -sample -show-sec-info-only %t.5.output  | FileCheck %s -check-prefix=NOSYMLIST
+
+; NOSYMLIST: ProfileSymbolListSection {{.*}} Size: 0

llvm/tools/llvm-profdata/llvm-profdata.cpp

 }
 
 static void
 mergeSampleProfile(const WeightedFileVector &Inputs, SymbolRemapper *Remapper,
                    StringRef OutputFilename, ProfileFormat OutputFormat,
                    StringRef ProfileSymbolListFile, bool CompressAllSections,
                    bool UseMD5, bool GenPartialProfile, bool GenCSNestedProfile,
                    bool SampleMergeColdContext, bool SampleTrimColdContext,
-                   bool SampleColdContextFrameDepth, FailureMode FailMode) {
+                   bool SampleColdContextFrameDepth, FailureMode FailMode,
+                   bool DropProfileSymbolList) {
   using namespace sampleprof;
   SampleProfileMap ProfileMap;
   SmallVector<std::unique_ptr<sampleprof::SampleProfileReader>, 5> Readers;
   LLVMContext Context;
   sampleprof::ProfileSymbolList WriterList;
   std::optional<bool> ProfileIsProbeBased;
   std::optional<bool> ProfileIsCS;
   for (const auto &Input : Inputs) {
for (SampleProfileMap::iterator I = Profiles.begin(), E = Profiles.end();
       MergeResult(Result, ProfileMap[FContext].merge(Samples, Input.Weight));
       if (Result != sampleprof_error::success) {
         std::error_code EC = make_error_code(Result);
         handleMergeWriterError(errorCodeToError(EC), Input.Filename,
                                FContext.toString());
       }
     }
 
+    if (!DropProfileSymbolList) {
       std::unique_ptr<sampleprof::ProfileSymbolList> ReaderList =
           Reader->getProfileSymbolList();
       if (ReaderList)
         WriterList.merge(*ReaderList);
     }
+  }
 
   if (ProfileIsCS && (SampleMergeColdContext || SampleTrimColdContext)) {
     // Use threshold calculated from profile summary unless specified.
     SampleProfileSummaryBuilder Builder(ProfileSummaryBuilder::DefaultCutoffs);
     auto Summary = Builder.computeSummaryForProfiles(ProfileMap);
     uint64_t SampleProfColdThreshold =
         ProfileSummaryBuilder::getColdCountThreshold(
             (Summary->getDetailedSummary()));
cl::opt<bool> GenCSNestedProfile(
       "gen-cs-nested-profile", cl::Hidden, cl::init(false),
       cl::desc("Generate nested function profiles for CSSPGO"));
   cl::opt<std::string> DebugInfoFilename(
       "debug-info", cl::init(""),
       cl::desc("Use the provided debug info to correlate the raw profile."));
   cl::opt<std::string> ProfiledBinary(
       "profiled-binary", cl::init(""),
       cl::desc("Path to binary from which the profile was collected."));
+  cl::opt<bool> DropProfileSymbolList(
+      "drop-profile-symbol-list", cl::init(false), cl::Hidden,
+      cl::desc("Drop the profile symbol list when merging AutoFDO profiles "
+               "(only meaningful for -sample)"));
 
   cl::ParseCommandLineOptions(argc, argv, "LLVM profile data merger\n");
 
   WeightedFileVector WeightedInputs;
   for (StringRef Filename : InputFilenames)
     addWeightedInput(WeightedInputs, {std::string(Filename), 1});
   for (StringRef WeightedFilename : WeightedInputFilenames)
     addWeightedInput(WeightedInputs, parseWeightedFile(WeightedFilename));
if (!SupplInstrWithSample.empty()) {
     return 0;
   }
 
   if (ProfileKind == instr)
     mergeInstrProfile(WeightedInputs, DebugInfoFilename, Remapper.get(),
                       OutputFilename, OutputFormat, OutputSparse, NumThreads,
                       FailureMode, ProfiledBinary);
   else
-    mergeSampleProfile(WeightedInputs, Remapper.get(), OutputFilename,
-                       OutputFormat, ProfileSymbolListFile, CompressAllSections,
-                       UseMD5, GenPartialProfile, GenCSNestedProfile,
-                       SampleMergeColdContext, SampleTrimColdContext,
-                       SampleColdContextFrameDepth, FailureMode);
+    mergeSampleProfile(
+        WeightedInputs, Remapper.get(), OutputFilename, OutputFormat,
+        ProfileSymbolListFile, CompressAllSections, UseMD5, GenPartialProfile,
+        GenCSNestedProfile, SampleMergeColdContext, SampleTrimColdContext,
+        SampleColdContextFrameDepth, FailureMode, DropProfileSymbolList);
   return 0;
 }
 
 /// Computer the overlap b/w profile BaseFilename and profile TestFilename.
 static void overlapInstrProfile(const std::string &BaseFilename,
                                 const std::string &TestFilename,
                                 const OverlapFuncFilters &FuncFilter,
                                 raw_fd_ostream &OS, bool IsCS) {