Removing null operations in the PSyIR frontend?

[arporter]

The pre-processed code of NEMO often ends up with expressions like limit + 0, presumably because of the tiling or some such. It will make comparing loop bounds simpler (in the future) if we simplified these expressions. This might feed in to #3310 too as the shortcut that @hiker has found for that problem won't work if we have a + 0 expression.

I'm therefore proposing that we tweak the fparser2 frontend slightly to spot this situation. We can update the handler for binary_operation like so:

--- a/src/psyclone/psyir/frontend/fparser2.py
+++ b/src/psyclone/psyir/frontend/fparser2.py
@@ -4943,6 +4943,14 @@ class Fparser2Reader():
        binary_op = BinaryOperation(operator, parent=parent)
         self.process_nodes(parent=binary_op, nodes=[arg_nodes[0]])
         self.process_nodes(parent=binary_op, nodes=[arg_nodes[1]])
+        if operator in [BinaryOperation.Operator.ADD,
+                        BinaryOperation.Operator.SUB]:
+            arg1 = binary_op.operands[1]
+            if isinstance(arg1, Literal) and arg1.value == "0":
+                arg0 = binary_op.operands[0].detach()
+                del binary_op
+                return arg0
+            
         return binary_op

Apart from the fact that the binary-operation handler can now return something that isn't a BinaryOperation, are there any other drawbacks @LonelyCat124 and @sergisiso?

[hiker]

Yes, that change would indeed help (assuming that we then have indeed a Reference instead of a BinaryOp). Might it be worth to also check for 0+limit? Some people have (imho) an odd order of operands :)