[NFC][RISCV] Move calculations of SDNode policy operand idx to a separate function

[asi-sc]

Summary

Since there is no guaranteed correspondence of SDNode and MI operands, we need
getters simular to RISCVII::get*OpNum for SDNodes.

More uses of getVecPolicyOpIdx will be added in D130895.

[craig.topper]

LGTM

[arcbbb]

LGTM

[asi-sc]

@arcbbb, could you please submit the patch on my behalf? Author: Anton Sidorenko <[e-mail]>
Thanks.

llvm/lib/Target/RISCV/RISCVISelDAGToDAG.cpp

 #define GET_RISCVVLETable_IMPL
 #define GET_RISCVVSETable_IMPL
 #define GET_RISCVVLXTable_IMPL
 #define GET_RISCVVSXTable_IMPL
 #define GET_RISCVMaskedPseudosTable_IMPL
 #include "RISCVGenSearchableTables.inc"
 } // namespace llvm::RISCV
 
+static unsigned getLastNonGlueOrChainOpIdx(const SDNode *Node) {
+  assert(Node->getNumOperands() > 0 && "Node with no operands");
+  unsigned LastOpIdx = Node->getNumOperands() - 1;
+  if (Node->getOperand(LastOpIdx).getValueType() == MVT::Glue)
+    --LastOpIdx;
+  if (Node->getOperand(LastOpIdx).getValueType() == MVT::Other)
+    --LastOpIdx;
+  return LastOpIdx;
+}
+
+static unsigned getVecPolicyOpIdx(const SDNode *Node, const MCInstrDesc &MCID) {
+  assert(RISCVII::hasVecPolicyOp(MCID.TSFlags));
+  (void)MCID;
+  return getLastNonGlueOrChainOpIdx(Node);
+}
+
 void RISCVDAGToDAGISel::PreprocessISelDAG() {
   SelectionDAG::allnodes_iterator Position = CurDAG->allnodes_end();
 
   bool MadeChange = false;
   while (Position != CurDAG->allnodes_begin()) {
     SDNode *N = &*--Position;
     if (N->use_empty())
       continue;
bool RISCVDAGToDAGISel::doPeepholeMaskedRVV(SDNode *N) {
 
   // Retrieve the tail policy operand index, if any.
   Optional<unsigned> TailPolicyOpIdx;
   const RISCVInstrInfo &TII = *Subtarget->getInstrInfo();
   const MCInstrDesc &MaskedMCID = TII.get(N->getMachineOpcode());
 
   bool IsTA = true;
   if (RISCVII::hasVecPolicyOp(MaskedMCID.TSFlags)) {
-    // The last operand of the pseudo is the policy op, but we might have a
-    // Glue operand last. We might also have a chain.
-    TailPolicyOpIdx = N->getNumOperands() - 1;
-    if (N->getOperand(*TailPolicyOpIdx).getValueType() == MVT::Glue)
-      (*TailPolicyOpIdx)--;
-    if (N->getOperand(*TailPolicyOpIdx).getValueType() == MVT::Other)
-      (*TailPolicyOpIdx)--;
-
+    TailPolicyOpIdx = getVecPolicyOpIdx(N, MaskedMCID);
     if (!(N->getConstantOperandVal(*TailPolicyOpIdx) &
           RISCVII::TAIL_AGNOSTIC)) {
       // Keep the true-masked instruction when there is no unmasked TU
       // instruction
       if (I->UnmaskedTUPseudo == I->MaskedPseudo && !N->getOperand(0).isUndef())
         return false;
       // We can't use TA if the tie-operand is not IMPLICIT_DEF
       if (!N->getOperand(0).isUndef())