[llvm][NFC] Use SDValue::getConstantOperandAPInt(i) where possible

The helper function allows examples like
`cast<ConstantSDNode>(Op.getOperand(0))->getAPIntValue();` to be changed
to `Op.getConstantOperandAPInt(0);`.

See #76708 for further context. Although there are far fewer
opportunities for replacement, I used a similar git grep and sed combo
as before, given I already had it to hand:

`git grep -l "cast<ConstantSDNode>\(.*->getOperand\(.*\)\)->getAPIntValue\(\)" | xargs sed -E -i 's/cast<ConstantSDNode>\((.*)->getOperand\((.*)\)\)->getAPIntValue\(\)/\1->getConstantOperandAPInt(\2)/'`
and
`git grep -l
"cast<ConstantSDNode>\(.*\.getOperand\(.*\)\)->getAPIntValue\(\)" |
xargs sed -E -i
's/cast<ConstantSDNode>\((.*)\.getOperand\((.*)\)\)->getAPIntValue\(\)/\1.getConstantOperandAPInt(\2)/'`

Author: asb

llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp

@@ -5470,7 +5470,7 @@ static SDValue FoldBUILD_VECTOR(const SDLoc &DL, EVT VT,
         Ops[i].getOperand(0).getValueType() != VT ||
         (IdentitySrc && Ops[i].getOperand(0) != IdentitySrc) ||
         !isa<ConstantSDNode>(Ops[i].getOperand(1)) ||
-        cast<ConstantSDNode>(Ops[i].getOperand(1))->getAPIntValue() != i) {
+        Ops[i].getConstantOperandAPInt(1) != i) {
       IsIdentity = false;
       break;
     }

llvm/lib/Target/AArch64/AArch64ISelLowering.cpp

@@ -14245,7 +14245,7 @@ SDValue AArch64TargetLowering::LowerVSCALE(SDValue Op,
   assert(VT != MVT::i64 && "Expected illegal VSCALE node");
 
   SDLoc DL(Op);
-  APInt MulImm = cast<ConstantSDNode>(Op.getOperand(0))->getAPIntValue();
+  APInt MulImm = Op.getConstantOperandAPInt(0);
   return DAG.getZExtOrTrunc(DAG.getVScale(DL, MVT::i64, MulImm.sext(64)), DL,
                             VT);
 }
@@ -18341,7 +18341,7 @@ static bool isEssentiallyExtractHighSubvector(SDValue N) {
     return false;
   if (N.getOperand(0).getValueType().isScalableVector())
     return false;
-  return cast<ConstantSDNode>(N.getOperand(1))->getAPIntValue() ==
+  return N.getConstantOperandAPInt(1) ==
          N.getOperand(0).getValueType().getVectorNumElements() / 2;
 }
 

llvm/lib/Target/AMDGPU/AMDGPUISelDAGToDAG.cpp

@@ -724,7 +724,7 @@ bool AMDGPUDAGToDAGISel::isUnneededShiftMask(const SDNode *N,
                                              unsigned ShAmtBits) const {
   assert(N->getOpcode() == ISD::AND);
 
-  const APInt &RHS = cast<ConstantSDNode>(N->getOperand(1))->getAPIntValue();
+  const APInt &RHS = N->getConstantOperandAPInt(1);
   if (RHS.countr_one() >= ShAmtBits)
     return true;
 

llvm/lib/Target/ARM/ARMISelLowering.cpp

@@ -14841,14 +14841,14 @@ static SDValue ParseBFI(SDNode *N, APInt &ToMask, APInt &FromMask) {
   assert(N->getOpcode() == ARMISD::BFI);
 
   SDValue From = N->getOperand(1);
-  ToMask = ~cast<ConstantSDNode>(N->getOperand(2))->getAPIntValue();
+  ToMask = ~N->getConstantOperandAPInt(2);
   FromMask = APInt::getLowBitsSet(ToMask.getBitWidth(), ToMask.popcount());
 
   // If the Base came from a SHR #C, we can deduce that it is really testing bit
   // #C in the base of the SHR.
   if (From->getOpcode() == ISD::SRL &&
       isa<ConstantSDNode>(From->getOperand(1))) {
-    APInt Shift = cast<ConstantSDNode>(From->getOperand(1))->getAPIntValue();
+    APInt Shift = From->getConstantOperandAPInt(1);
     assert(Shift.getLimitedValue() < 32 && "Shift too large!");
     FromMask <<= Shift.getLimitedValue(31);
     From = From->getOperand(0);

llvm/lib/Target/Mips/MipsISelDAGToDAG.cpp

@@ -330,7 +330,7 @@ bool MipsDAGToDAGISel::isUnneededShiftMask(SDNode *N,
                                            unsigned ShAmtBits) const {
   assert(N->getOpcode() == ISD::AND && "Unexpected opcode");
 
-  const APInt &RHS = cast<ConstantSDNode>(N->getOperand(1))->getAPIntValue();
+  const APInt &RHS = N->getConstantOperandAPInt(1);
   if (RHS.countr_one() >= ShAmtBits) {
     LLVM_DEBUG(
         dbgs()

llvm/lib/Target/Mips/MipsSEISelLowering.cpp

@@ -1519,7 +1519,7 @@ static SDValue lowerMSABitClearImm(SDValue Op, SelectionDAG &DAG) {
   SDLoc DL(Op);
   EVT ResTy = Op->getValueType(0);
   APInt BitImm = APInt(ResTy.getScalarSizeInBits(), 1)
-                 << cast<ConstantSDNode>(Op->getOperand(2))->getAPIntValue();
+                 << Op->getConstantOperandAPInt(2);
   SDValue BitMask = DAG.getConstant(~BitImm, DL, ResTy);
 
   return DAG.getNode(ISD::AND, DL, ResTy, Op->getOperand(1), BitMask);

llvm/lib/Target/X86/X86ISelDAGToDAG.cpp

@@ -487,7 +487,7 @@ namespace {
     // from PatFrags in tablegen.
     bool isUnneededShiftMask(SDNode *N, unsigned Width) const {
       assert(N->getOpcode() == ISD::AND && "Unexpected opcode");
-      const APInt &Val = cast<ConstantSDNode>(N->getOperand(1))->getAPIntValue();
+      const APInt &Val = N->getConstantOperandAPInt(1);
 
       if (Val.countr_one() >= Width)
         return true;