Avoid pointless canonicalize when using Dwarf names

[marksantaniello]

Summary

CPU profile indicated memcmp was hot due to the two rfind calls in
getCanonicalFnName. If UseSymbolTable is false, we can avoid the cost entirely.

For CSSPGO profiles I've measured ~5% speedup with this change.

Profile similarity before/after matches 100%.

[wenlei]

lgtm, thanks for the fix.

llvm/tools/llvm-profgen/ProfiledBinary.h

 
 using AddressRange = std::pair<uint64_t, uint64_t>;
 
 class ProfiledBinary {
   // Absolute path of the executable binary.
   std::string Path;
   // Path of the debug info binary.
   std::string DebugBinaryPath;
-  // Path of symbolizer path which should be pointed to binary with debug info.
-  StringRef SymbolizerPath;
   // The target triple.
   Triple TheTriple;
+  // Path of symbolizer path which should be pointed to binary with debug info.
+  StringRef SymbolizerPath;
+  // Options used to configure the symbolizer
+  symbolize::LLVMSymbolizer::Options SymbolizerOpts;
   // The runtime base address that the first executable segment is loaded at.
   uint64_t BaseAddress = 0;
   // The runtime base address that the first loadabe segment is loaded at.
   uint64_t FirstLoadableAddress = 0;
   // The preferred load address of each executable segment.
   std::vector<uint64_t> PreferredTextSegmentAddresses;
   // The file offset of each executable segment.
   std::vector<uint64_t> TextSegmentOffsets;
class ProfiledBinary {
   void decodePseudoProbe(const ELFObjectFileBase *Obj);
 
   void
   checkUseFSDiscriminator(const ELFObjectFileBase *Obj,
                           std::map<SectionRef, SectionSymbolsTy> &AllSymbols);
 
   // Set up disassembler and related components.
   void setUpDisassembler(const ELFObjectFileBase *Obj);
-  void setupSymbolizer();
+  symbolize::LLVMSymbolizer::Options getSymbolizerOpts() const;
 
   // Load debug info of subprograms from DWARF section.
   void loadSymbolsFromDWARF(ObjectFile &Obj);
 
   // Load debug info from DWARF unit.
   void loadSymbolsFromDWARFUnit(DWARFUnit &CompilationUnit);
 
   // Create elf symbol to its start address mapping.
void inferMissingFrames(const SmallVectorImpl<uint64_t> &Context,
                           SmallVectorImpl<uint64_t> &NewContext);
 
   // Load the symbols from debug table and populate into symbol list.
   void populateSymbolListFromDWARF(ProfileSymbolList &SymbolList);
 
   SampleContextFrameVector
   getFrameLocationStack(uint64_t Address, bool UseProbeDiscriminator = false) {
     InstructionPointer IP(this, Address);
-    return symbolize(IP, true, UseProbeDiscriminator);
+    return symbolize(IP, SymbolizerOpts.UseSymbolTable, UseProbeDiscriminator);
   }
 
   const SampleContextFrameVector &
   getCachedFrameLocationStack(uint64_t Address,
                               bool UseProbeDiscriminator = false) {
     auto I = AddressToLocStackMap.emplace(Address, SampleContextFrameVector());
     if (I.second) {
       I.first->second = getFrameLocationStack(Address, UseProbeDiscriminator);

llvm/tools/llvm-profgen/ProfiledBinary.cpp

for (const auto &ChildNode : ProbeNode.getChildren()) {
     trackInlineesOptimizedAway(ProbeDecoder, *ChildNode.second.get(),
                                ProbeContext);
   }
 
   ProbeContext.pop_back();
 }
 
 ProfiledBinary::ProfiledBinary(const StringRef ExeBinPath,
                                const StringRef DebugBinPath)
-    : Path(ExeBinPath), DebugBinaryPath(DebugBinPath), ProEpilogTracker(this),
+    : Path(ExeBinPath), DebugBinaryPath(DebugBinPath),
+      SymbolizerOpts(getSymbolizerOpts()), ProEpilogTracker(this),
+      Symbolizer(std::make_unique<symbolize::LLVMSymbolizer>(SymbolizerOpts)),
       TrackFuncContextSize(EnableCSPreInliner && UseContextCostForPreInliner) {
   // Point to executable binary if debug info binary is not specified.
   SymbolizerPath = DebugBinPath.empty() ? ExeBinPath : DebugBinPath;
-  setupSymbolizer();
   if (InferMissingFrames)
     MissingContextInferrer = std::make_unique<MissingFrameInferrer>(this);
   load();
 }
 
 ProfiledBinary::~ProfiledBinary() {}
 
 void ProfiledBinary::warnNoFuncEntry() {

 }
 
 void ProfiledBinary::populateSymbolListFromDWARF(
     ProfileSymbolList &SymbolList) {
   for (auto &I : StartAddrToFuncRangeMap)
     SymbolList.add(I.second.getFuncName());
 }
 
-void ProfiledBinary::setupSymbolizer() {
+symbolize::LLVMSymbolizer::Options ProfiledBinary::getSymbolizerOpts() const {
   symbolize::LLVMSymbolizer::Options SymbolizerOpts;
   SymbolizerOpts.PrintFunctions =
       DILineInfoSpecifier::FunctionNameKind::LinkageName;
   SymbolizerOpts.Demangle = false;
   SymbolizerOpts.DefaultArch = TheTriple.getArchName().str();
   SymbolizerOpts.UseSymbolTable = false;
   SymbolizerOpts.RelativeAddresses = false;
   SymbolizerOpts.DWPName = DWPPath;
-  Symbolizer = std::make_unique<symbolize::LLVMSymbolizer>(SymbolizerOpts);
+  return SymbolizerOpts;
 }
 
 SampleContextFrameVector ProfiledBinary::symbolize(const InstructionPointer &IP,
                                                    bool UseCanonicalFnName,
                                                    bool UseProbeDiscriminator) {
   assert(this == IP.Binary &&
          "Binary should only symbolize its own instruction");
   auto Addr = object::SectionedAddress{IP.Address,