[llvm] [SelectionDAG] Improve type legalisation for PARTIAL_REDUCE_MLA (PR #130935)

[Benjamin Maxwell via llvm-commits]

================
@@ -1668,6 +1668,12 @@ class TargetLoweringBase {
     return Action == Legal || Action == Custom;
   }
 
+  /// Return true if a PARTIAL_REDUCE_U/SMLA node with the specified types is
+  /// legal for this target.
+  bool isPartialReduceMLALegal(EVT AccVT, EVT InputVT) const {
+    return getPartialReduceMLAAction(AccVT, InputVT) == Legal;
+  }
+
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MacDue wrote:

This is unused in the current patch. 
```suggestion
```

https://github.com/llvm/llvm-project/pull/130935