[IROutliner] Avoid repeated hash lookups (NFC) (#107726)

Author: kazutakahirata

llvm/lib/Transforms/IPO/IROutliner.cpp

@@ -1333,11 +1333,10 @@ findExtractedOutputToOverallOutputMapping(Module &M, OutlinableRegion &Region,
       if (!isa<PointerType>(Group.ArgumentTypes[Jdx]))
         continue;
 
-      if (AggArgsUsed.contains(Jdx))
+      if (!AggArgsUsed.insert(Jdx).second)
         continue;
 
       TypeFound = true;
-      AggArgsUsed.insert(Jdx);
       Region.ExtractedArgToAgg.insert(std::make_pair(OriginalIndex, Jdx));
       Region.AggArgToExtracted.insert(std::make_pair(Jdx, OriginalIndex));
       AggArgIdx = Jdx;