[TargetLowering] Handle vector types in expandFixedPointMul

In TargetLowering::expandFixedPointMul when expanding fixed point
multiplication, and when using a widened MUL as strategy for the
lowering, there was a bug resulting in assertion failures like this:
   Assertion `VT.isVector() == N1.getValueType().isVector() &&
   "SIGN_EXTEND result type type should be vector iff the operand "
   "type is vector!"' failed.

Problem was that we did not consider that VT could be a vector type
when setting up the WideVT. This patch should fix that bug.

Author: bjope

llvm/lib/CodeGen/SelectionDAG/TargetLowering.cpp

@@ -10782,6 +10782,9 @@ TargetLowering::expandFixedPointMul(SDNode *Node, SelectionDAG &DAG) const {
   unsigned LoHiOp = Signed ? ISD::SMUL_LOHI : ISD::UMUL_LOHI;
   unsigned HiOp = Signed ? ISD::MULHS : ISD::MULHU;
   EVT WideVT = EVT::getIntegerVT(*DAG.getContext(), VTSize * 2);
+  if (VT.isVector())
+    WideVT =
+        EVT::getVectorVT(*DAG.getContext(), WideVT, VT.getVectorElementCount());
   if (isOperationLegalOrCustom(LoHiOp, VT)) {
     SDValue Result = DAG.getNode(LoHiOp, dl, DAG.getVTList(VT, VT), LHS, RHS);
     Lo = Result.getValue(0);

llvm/test/CodeGen/AArch64/smul_fix.ll

@@ -137,3 +137,17 @@ define <4 x i64> @vec3(<4 x i64> %x, <4 x i64> %y) nounwind {
   %tmp = call <4 x i64> @llvm.smul.fix.v4i64(<4 x i64> %x, <4 x i64> %y, i32 32)
   ret <4 x i64> %tmp
 }
+
+define <4 x i16> @widemul(<4 x i16> %x, <4 x i16> %y) nounwind {
+; CHECK-LABEL: widemul:
+; CHECK:       // %bb.0:
+; CHECK-NEXT:    smull v0.4s, v0.4h, v1.4h
+; CHECK-NEXT:    shrn v1.4h, v0.4s, #16
+; CHECK-NEXT:    xtn v2.4h, v0.4s
+; CHECK-NEXT:    add v1.4h, v1.4h, v1.4h
+; CHECK-NEXT:    shl v0.4h, v1.4h, #13
+; CHECK-NEXT:    usra v0.4h, v2.4h, #2
+; CHECK-NEXT:    ret
+  %tmp = call <4 x i16> @llvm.smul.fix.v4i16(<4 x i16> %x, <4 x i16> %y, i32 2)
+  ret <4 x i16> %tmp
+}