[InstCombine] Avoid repeated hash lookups (NFC) (#124243)

Author: kazutakahirata

llvm/lib/Transforms/InstCombine/InstCombineVectorOps.cpp

@@ -3060,14 +3060,10 @@ Instruction *InstCombinerImpl::visitShuffleVectorInst(ShuffleVectorInst &SVI) {
       unsigned SrcElemsPerTgtElem = TgtElemBitWidth / SrcElemBitWidth;
       assert(SrcElemsPerTgtElem);
       BegIdx /= SrcElemsPerTgtElem;
-      bool BCAlreadyExists = NewBCs.contains(CastSrcTy);
-      auto *NewBC =
-          BCAlreadyExists
-              ? NewBCs[CastSrcTy]
-              : Builder.CreateBitCast(V, CastSrcTy, SVI.getName() + ".bc");
-      if (!BCAlreadyExists)
-        NewBCs[CastSrcTy] = NewBC;
-      auto *Ext = Builder.CreateExtractElement(NewBC, BegIdx,
+      auto [It, Inserted] = NewBCs.try_emplace(CastSrcTy);
+      if (Inserted)
+        It->second = Builder.CreateBitCast(V, CastSrcTy, SVI.getName() + ".bc");
+      auto *Ext = Builder.CreateExtractElement(It->second, BegIdx,
                                                SVI.getName() + ".extract");
       // The shufflevector isn't being replaced: the bitcast that used it
       // is. InstCombine will visit the newly-created instructions.