[llvm] [SelectionDAG] Add PARTIAL_REDUCE_U/SMLA ISD Nodes (PR #125207)

[Sander de Smalen via llvm-commits]

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@@ -12188,3 +12189,51 @@ SDValue TargetLowering::scalarizeExtractedVectorLoad(EVT ResultVT,
 
   return Load;
 }
+
+SDValue TargetLowering::expandPartialReduceMLA(SDLoc DL, SDValue Acc,
+                                               SDValue Input1, SDValue Input2,
+                                               SelectionDAG &DAG) const {
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sdesmalen-arm wrote:

Could you change this so that `expandPartialReduceMLA` only takes a `Node *` and a `DAG`? That's what the other lowering functions seem to do.

That does mean rejigging the code in SelectionDAGBuilder a little bit to return a newly created node, and there is a function in `performIntrinsicCombine` as well that would need updating to take a `PARTIAL_REDUCE_UMLA` node.

https://github.com/llvm/llvm-project/pull/125207