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

[Paul Walker via llvm-commits]

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@@ -1571,6 +1581,11 @@ AArch64TargetLowering::AArch64TargetLowering(const TargetMachine &TM,
       setOperationAction(ISD::MSTORE, VT, Custom);
     }
 
+    for (MVT VT : MVT::scalable_vector_valuetypes()) {
+      setOperationAction(ISD::PARTIAL_REDUCE_UMLA, VT, Expand);
+      setOperationAction(ISD::PARTIAL_REDUCE_SMLA, VT, Expand);
+    }
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paulwalker-arm wrote:

Given this new node is effectively opt-in I suggest adding an entry to `TargetLoweringBase::initActions()` so the operation is marked as expand for all value types.  Then in your follow-on patches you can selectively make some of them legal.

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