[llvm] [SystemZ] Add custom handling of legal vectors with reduce-add. (PR #88495)

[Ulrich Weigand via llvm-commits]

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@@ -9505,3 +9514,39 @@ SDValue SystemZTargetLowering::lowerGET_ROUNDING(SDValue Op,
 
   return DAG.getMergeValues({RetVal, Chain}, dl);
 }
+
+SDValue SystemZTargetLowering::lowerVECREDUCE_ADD(SDValue Op,
+                                                  SelectionDAG &DAG) const {
+  EVT VT = Op.getValueType();
+  Op = Op.getOperand(0);
+  EVT OpVT = Op.getValueType();
+
+  assert(OpVT.isVector() && "Operand type for VECREDUCE_ADD is not a vector.");
+
+  SDLoc DL(Op);
+
+  // load a 0 vector for the third operand of VSUM.
+  SDValue Zero = DAG.getSplatBuildVector(OpVT, DL, DAG.getConstant(0, DL, VT));
+
+  // execute VSUM.
+  switch (OpVT.getScalarSizeInBits()) {
+  case 8:
+  case 16:
+    Op = DAG.getNode(SystemZISD::VSUM, DL, MVT::v4i32, Op,
+                     DAG.getBitcast(OpVT, Zero));
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uweigand wrote:

Doesn't Zero already have the correct type here, so we don't need the bitcast?

https://github.com/llvm/llvm-project/pull/88495