[Scalar] Avoid repeated hash lookups (NFC) (#112486)

Author: kazutakahirata

llvm/lib/Transforms/Scalar/Float2Int.cpp

@@ -398,9 +398,9 @@ bool Float2IntPass::validateAndTransform(const DataLayout &DL) {
 }
 
 Value *Float2IntPass::convert(Instruction *I, Type *ToTy) {
-  if (ConvertedInsts.contains(I))
+  if (auto It = ConvertedInsts.find(I); It != ConvertedInsts.end())
     // Already converted this instruction.
-    return ConvertedInsts[I];
+    return It->second;
 
   SmallVector<Value*,4> NewOperands;
   for (Value *V : I->operands()) {