[CodeGen] Avoid repeated hash lookups (NFC) (#123016)

Author: kazutakahirata

llvm/lib/CodeGen/CodeGenPrepare.cpp

@@ -7690,8 +7690,8 @@ bool CodeGenPrepare::tryToSinkFreeOperands(Instruction *I) {
     // sunk instruction uses, if it is part of a chain that has already been
     // sunk.
     Instruction *OldI = cast<Instruction>(U->getUser());
-    if (NewInstructions.count(OldI))
-      NewInstructions[OldI]->setOperand(U->getOperandNo(), NI);
+    if (auto It = NewInstructions.find(OldI); It != NewInstructions.end())
+      It->second->setOperand(U->getOperandNo(), NI);
     else
       U->set(NI);
     Changed = true;