[llvm] [DAGCombiner] Add DAG combine for PARTIAL_REDUCE_MLA when no mul op (PR #131326)

[Sander de Smalen via llvm-commits]

================
@@ -12669,6 +12679,48 @@ SDValue DAGCombiner::visitPARTIAL_REDUCE_MLA(SDNode *N) {
                      RHSExtOp);
 }
 
+// Makes partial.reduce.umla(acc, zext(op1), splat(1)) into
+// partial.reduce.umla(acc, op, splat(trunc(1)))
+// Makes partial.reduce.smla(acc, sext(op1), splat(1)) into
+// partial.reduce.smla(acc, op, splat(trunc(1)))
+SDValue DAGCombiner::foldPartialReduceMLANoMulOp(SDNode *N) {
+  SDLoc DL(N);
+  SDValue Acc = N->getOperand(0);
+  SDValue Op1 = N->getOperand(1);
+  SDValue Op2 = N->getOperand(2);
+
+  APInt ConstantOne;
+  if (!ISD::isConstantSplatVector(Op2.getNode(), ConstantOne) ||
+      !ConstantOne.isOne())
----------------
sdesmalen-arm wrote:

nit:
```suggestion
  APInt C;
  if (!ISD::isConstantSplatVector(Op2.getNode(), C) || !C.isOne())
```

https://github.com/llvm/llvm-project/pull/131326