[RISCV] Disable combineToVCPOP for illegal scalable vector types.

This transform creates target specific instructions which must have
legal types. We were checking this for fixed vectors, but not scalable
vectors. This caused a crash with <vscale x 1 x i1> which isn't legal
for Zve32x.

Author: topperc

llvm/lib/Target/RISCV/RISCVISelLowering.cpp

@@ -18798,6 +18798,10 @@ static SDValue combineToVCPOP(SDNode *N, SelectionDAG &DAG,
   if (!SrcMVT.isVector() || SrcMVT.getVectorElementType() != MVT::i1)
     return SDValue();
 
+  const TargetLowering &TLI = DAG.getTargetLoweringInfo();
+  if (!TLI.isTypeLegal(SrcMVT))
+    return SDValue();
+
   // Check that destination type is large enough to hold result without
   // overflow.
   if (Opc == ISD::VECREDUCE_ADD) {
@@ -18814,9 +18818,6 @@ static SDValue combineToVCPOP(SDNode *N, SelectionDAG &DAG,
 
   MVT ContainerVT = SrcMVT;
   if (SrcMVT.isFixedLengthVector()) {
-    if (!useRVVForFixedLengthVectorVT(SrcMVT, Subtarget))
-      return SDValue();
-
     ContainerVT = getContainerForFixedLengthVector(DAG, SrcMVT, Subtarget);
     Src = convertToScalableVector(ContainerVT, Src, DAG, Subtarget);
   }