[X86] combinei64TruncSrlConstant - sink EVT::getIntegerVT to ISD::ADD case only. NFC.

Don't bother creating the CleanUpVT variable unless its being used by the getZeroExtendInReg call in the ISD::ADD case

Noticed while triaging #141496

Author: RKSimon

llvm/lib/Target/X86/X86ISelLowering.cpp

@@ -54232,10 +54232,11 @@ static SDValue combinei64TruncSrlConstant(SDValue N, EVT VT, SelectionDAG &DAG,
   APInt NewOpConstVal = OpConst.lshr(SrlConst).trunc(VT.getSizeInBits());
   SDValue NewOpConst = DAG.getConstant(NewOpConstVal, DL, VT);
   SDValue NewOpNode = DAG.getNode(Opcode, DL, VT, Trunc, NewOpConst);
-  EVT CleanUpVT = EVT::getIntegerVT(*DAG.getContext(), 64 - SrlConstVal);
 
-  if (Opcode == ISD::ADD)
+  if (Opcode == ISD::ADD) {
+    EVT CleanUpVT = EVT::getIntegerVT(*DAG.getContext(), 64 - SrlConstVal);
     return DAG.getZeroExtendInReg(NewOpNode, DL, CleanUpVT);
+  }
   return NewOpNode;
 }