[flang][hlfir] Fixed assignment/finalization order for user-defined assignments. (#66736)

This patch places the finalization code for the RHS of a user-defined
assignment after the assignment code. The change only affects
standalone RegionAssignOp operations.

Author: vzakhari

flang/lib/Optimizer/HLFIR/Transforms/LowerHLFIROrderedAssignments.cpp

@@ -1112,7 +1112,22 @@ void OrderedAssignmentRewriter::generateSaveEntity(
     assert(inserted.second && "entity must have been emplaced");
     (void)inserted;
   } else {
-    generateCleanupIfAny(oldYield);
+    if (constructStack.empty() &&
+        mlir::isa<hlfir::RegionAssignOp>(region.getParentOp())) {
+      // Here the clean-up code is inserted after the original
+      // RegionAssignOp, so that the assignment code happens
+      // before the cleanup. We do this only for standalone
+      // operations, because the clean-up is handled specially
+      // during lowering of the parent constructs if any
+      // (e.g. see generateNoneElementalCleanupIfAny for
+      // WhereOp).
+      auto insertionPoint = builder.saveInsertionPoint();
+      builder.setInsertionPointAfter(region.getParentOp());
+      generateCleanupIfAny(oldYield);
+      builder.restoreInsertionPoint(insertionPoint);
+    } else {
+      generateCleanupIfAny(oldYield);
+    }
   }
 }