[Scalar] Avoid repeated hash lookups (NFC)

Author: kazutakahirata

llvm/lib/Transforms/Scalar/CallSiteSplitting.cpp

@@ -397,9 +397,10 @@ static void splitCallSite(CallBase &CB,
         continue;
       PHINode *NewPN = PHINode::Create(CurrentI->getType(), Preds.size());
       NewPN->setDebugLoc(CurrentI->getDebugLoc());
-      for (auto &Mapping : ValueToValueMaps)
-        NewPN->addIncoming(Mapping[CurrentI],
-                           cast<Instruction>(Mapping[CurrentI])->getParent());
+      for (auto &Mapping : ValueToValueMaps) {
+        Value *V = Mapping[CurrentI];
+        NewPN->addIncoming(V, cast<Instruction>(V)->getParent());
+      }
       NewPN->insertBefore(*TailBB, TailBB->begin());
       CurrentI->replaceAllUsesWith(NewPN);
     }