Remove constant local variable (#83850)

Remove isThisReturn, which always has the value false.
Replace its uses with false directly.

Author: Martin Wehking

llvm/lib/Target/AMDGPU/SIISelLowering.cpp

@@ -3598,7 +3598,6 @@ SDValue SITargetLowering::LowerCall(CallLoweringInfo &CLI,
   bool &IsTailCall = CLI.IsTailCall;
   bool IsVarArg = CLI.IsVarArg;
   bool IsSibCall = false;
-  bool IsThisReturn = false;
   MachineFunction &MF = DAG.getMachineFunction();
 
   if (Callee.isUndef() || isNullConstant(Callee)) {
@@ -3888,8 +3887,7 @@ SDValue SITargetLowering::LowerCall(CallLoweringInfo &CLI,
   // Handle result values, copying them out of physregs into vregs that we
   // return.
   return LowerCallResult(Chain, InGlue, CallConv, IsVarArg, Ins, DL, DAG,
-                         InVals, IsThisReturn,
-                         IsThisReturn ? OutVals[0] : SDValue());
+                         InVals, /*IsThisReturn=*/false, SDValue());
 }
 
 // This is identical to the default implementation in ExpandDYNAMIC_STACKALLOC,