[llvm] [AArch64][SVE] Add dot product lowering for PARTIAL_REDUCE_MLA node (PR #130933)

[Sander de Smalen via llvm-commits]

================
@@ -1639,6 +1639,26 @@ class TargetLoweringBase {
            getCondCodeAction(CC, VT) == Custom;
   }
 
+  /// Return how a PARTIAL_REDUCE_U/SMLA node with Acc type AccVT and Input type
+  /// InputVT should be treated. Either it's legal, needs to be promoted to a
+  /// larger size, needs to be expanded to some other code sequence, or the
+  /// target has a custom expander for it.
+  LegalizeAction getPartialReduceMLAAction(EVT AccVT, EVT InputVT) const {
+    PartialReduceActionTypes TypePair = {AccVT.getSimpleVT().SimpleTy,
+                                         InputVT.getSimpleVT().SimpleTy};
+    auto It = PartialReduceMLAActions.find(TypePair);
+    if (It != PartialReduceMLAActions.end())
+      return It->second;
+    return Expand;
----------------
sdesmalen-arm wrote:

minor nit: this can be further simplified to:
```suggestion
    auto It = PartialReduceMLAActions.find(
        {AccVT.getSimpleVT().SimpleTy, InputVT.getSimpleVT().SimpleTy});
    return It == PartialReduceMLAActions.end() ? Expand : It->second;
```

https://github.com/llvm/llvm-project/pull/130933