[llvm-dwarfdump] Fix slowdown in dwarfdump statistics.

[rdhindsa]

Summary

Fixed slowdown that happened after https://reviews.llvm.org/D96045,

While running dwarfdump --statistics, it spends more than 50% of the time in collectZeroCovInlinedVars function.

In function collectStatsForObjectFile, variable InlinedFnsToBeProcessed is being created outside the for loop. The inline functions to be processed are appended and processed multiple times. Hence, moving the creation of that variable into the for loop which fixes the slowdown.

[dblaikie]

If there are cases where this causes the wrong/different answer (@rdhindsa you mentioned in some targets with this patch the statistics changed?) perhaps this patch could include a test demonstrating that bug/fix?

[rdhindsa]

This change is causing a difference in 2 dwarfdump statistics for a large binary with fission=yes.

I have commented on the original patch and will let the author of the patch look at it, since I am not very familiar with it.

llvm/tools/llvm-dwarfdump/Statistics.cpp

 /// compilers is.
 bool dwarfdump::collectStatsForObjectFile(ObjectFile &Obj, DWARFContext &DICtx,
                                           const Twine &Filename,
                                           raw_ostream &OS) {
   StringRef FormatName = Obj.getFileFormatName();
   GlobalStats GlobalStats;
   LocationStats LocStats;
   InlinedVarsTyMap GlobalInlinedFnInfo;
-  InlinedFnInstacesTy InlinedFnsToBeProcessed;
   StringMap<PerFunctionStats> Statistics;
   for (const auto &CU : static_cast<DWARFContext *>(&DICtx)->compile_units()) {
     if (DWARFDie CUDie = CU->getNonSkeletonUnitDIE(false)) {
+      InlinedFnInstacesTy InlinedFnsToBeProcessed;
       collectStatsRecursive(CUDie, "/", "g", 0, 0, Statistics, GlobalStats,
                             LocStats, GlobalInlinedFnInfo,
                             InlinedFnsToBeProcessed);
 
       collectZeroCovInlinedVars(CUDie.getDwarfUnit(), GlobalStats, LocStats,
                                 GlobalInlinedFnInfo, InlinedFnsToBeProcessed);
     }
   }