[SelectionDAG] Correctly determine the VECREDUCE_SEQ_FMUL action

[frasercrmck]

Summary

The LegalizeAction for this node should follow the logic for
VECREDUCE_SEQ_FADD and be determined using the vector operand's type.

here isn't an in-tree target that makes use of this, but I think it's safe to
say this is how it should behave, should a target want to customize the action
for this node.

[dmgreen]

Looks correct to me, and I don't see anywhere else where VECREDUCE_SEQ_FMUL is missing compared to VECREDUCE_SEQ_FADD

[frasercrmck]

• rebase to give the buildbots a go

llvm/lib/CodeGen/SelectionDAG/LegalizeDAG.cpp

#endif
   case ISD::VECREDUCE_UMAX:
   case ISD::VECREDUCE_UMIN:
   case ISD::VECREDUCE_FMAX:
   case ISD::VECREDUCE_FMIN:
     Action = TLI.getOperationAction(
         Node->getOpcode(), Node->getOperand(0).getValueType());
     break;
   case ISD::VECREDUCE_SEQ_FADD:
+  case ISD::VECREDUCE_SEQ_FMUL:
     Action = TLI.getOperationAction(
         Node->getOpcode(), Node->getOperand(1).getValueType());
     break;
   default:
     if (Node->getOpcode() >= ISD::BUILTIN_OP_END) {
       Action = TargetLowering::Legal;
     } else {
       Action = TLI.getOperationAction(Node->getOpcode(), Node->getValueType(0));