[X86] Replace (void) with [[maybe_unused]] for some variables unused (or only used in asserts). NFC.

Author: RKSimon

llvm/lib/Target/X86/X86ISelLowering.cpp

@@ -4183,8 +4183,7 @@ static SDValue splitVectorIntUnary(SDValue Op, SelectionDAG &DAG,
                                    const SDLoc &dl) {
   // Make sure we only try to split 256/512-bit types to avoid creating
   // narrow vectors.
-  EVT VT = Op.getValueType();
-  (void)VT;
+  [[maybe_unused]] EVT VT = Op.getValueType();
   assert((Op.getOperand(0).getValueType().is256BitVector() ||
           Op.getOperand(0).getValueType().is512BitVector()) &&
          (VT.is256BitVector() || VT.is512BitVector()) && "Unsupported VT!");
@@ -4199,8 +4198,7 @@ static SDValue splitVectorIntUnary(SDValue Op, SelectionDAG &DAG,
 static SDValue splitVectorIntBinary(SDValue Op, SelectionDAG &DAG,
                                     const SDLoc &dl) {
   // Assert that all the types match.
-  EVT VT = Op.getValueType();
-  (void)VT;
+  [[maybe_unused]] EVT VT = Op.getValueType();
   assert(Op.getOperand(0).getValueType() == VT &&
          Op.getOperand(1).getValueType() == VT && "Unexpected VTs!");
   assert((VT.is256BitVector() || VT.is512BitVector()) && "Unsupported VT!");
@@ -23411,8 +23409,7 @@ static SDValue LowerVSETCC(SDValue Op, const X86Subtarget &Subtarget,
 
   assert(!IsStrict && "Strict SETCC only handles FP operands.");
 
-  MVT VTOp0 = Op0.getSimpleValueType();
-  (void)VTOp0;
+  [[maybe_unused]] MVT VTOp0 = Op0.getSimpleValueType();
   assert(VTOp0 == Op1.getSimpleValueType() &&
          "Expected operands with same type!");
   assert(VT.getVectorNumElements() == VTOp0.getVectorNumElements() &&