Re-implement explicit default assignment without reverting the memory footprint savings

Author: NickGuy-Arm

llvm/include/llvm/CodeGen/TargetLowering.h

@@ -1651,7 +1651,10 @@ class TargetLoweringBase {
     auto AccI = AccSVT.SimpleTy;
     auto InputI = InputSVT.SimpleTy;
     PartialReduceActionTypes TypePair = std::make_pair(AccI, InputI);
-    return PartialReduceMLAActions.lookup(TypePair);
+    auto It = PartialReduceMLAActions.find(TypePair);
+    if (It != PartialReduceMLAActions.end())
+      return It->second;
+    return Expand;
   }
 
   /// Return true if a PARTIAL_REDUCE_U/SMLA node with the specified types is

llvm/lib/CodeGen/TargetLoweringBase.cpp

@@ -835,9 +835,6 @@ void TargetLoweringBase::initActions() {
     setOperationAction(ISD::GET_FPENV, VT, Expand);
     setOperationAction(ISD::SET_FPENV, VT, Expand);
     setOperationAction(ISD::RESET_FPENV, VT, Expand);
-
-    for (MVT InputVT : MVT::all_valuetypes())
-      setPartialReduceMLAAction(VT, InputVT, Expand);
   }
 
   // Most targets ignore the @llvm.prefetch intrinsic.