[CSSPGO] Fix a typo in SampleContextTracker

[hoy]

Summary

Fixing a typo in SampleContextTracker to use debug name when debug linkage name is no present. This should only affect C programs.

Saw 0.6% perf win on Cinder which is mostly C code.

[wenlei]

Good catch, thanks for the fix!

[wmi]

Good catch.

llvm/lib/Transforms/IPO/SampleContextTracker.cpp

ContextTrieNode *SampleContextTracker::getContextFor(const DILocation *DIL) {
 
   // Use C++ linkage name if possible.
   const DILocation *PrevDIL = DIL;
   for (DIL = DIL->getInlinedAt(); DIL; DIL = DIL->getInlinedAt()) {
     StringRef Name = PrevDIL->getScope()->getSubprogram()->getLinkageName();
     if (Name.empty())
       Name = PrevDIL->getScope()->getSubprogram()->getName();
     S.push_back(
-        std::make_pair(FunctionSamples::getCallSiteIdentifier(DIL),
-                       PrevDIL->getScope()->getSubprogram()->getLinkageName()));
+        std::make_pair(FunctionSamples::getCallSiteIdentifier(DIL), Name));
     PrevDIL = DIL;
   }
 
   // Push root node, note that root node like main may only
   // a name, but not linkage name.
   StringRef RootName = PrevDIL->getScope()->getSubprogram()->getLinkageName();
   if (RootName.empty())
     RootName = PrevDIL->getScope()->getSubprogram()->getName();