(towards #3124) Make the loop variable as child of Loop instead of an attribute

src/psyclone/domain/gocean/transformations/gocean_const_loop_bounds_trans.py

@@ -253,7 +253,7 @@ def apply(self, node, options=None):
                 start_expr = "1"
             psyir = fortran_reader.psyir_from_expression(
                     start_expr, node.symbol_table)
-            loop.children[0].replace_with(psyir)
+            loop.start_expr.replace_with(psyir)
 
             # Set the upper bound
             stop_expr = bounds["stop"].format(start='2', stop=stop)
@@ -262,4 +262,4 @@ def apply(self, node, options=None):
                 stop_expr = "1"
             psyir = fortran_reader.psyir_from_expression(
                     stop_expr, node.symbol_table)
-            loop.children[1].replace_with(psyir)
+            loop.stop_expr.replace_with(psyir)

src/psyclone/domain/lfric/lfric_loop.py

@@ -41,7 +41,7 @@
     '''
 
 from psyclone.configuration import Config
-from psyclone.core import AccessType
+from psyclone.core import AccessType, VariablesAccessMap, Signature
 from psyclone.domain.common.psylayer import PSyLoop
 from psyclone.domain.lfric import LFRicConstants
 from psyclone.domain.lfric.lfric_kern import LFRicKern
@@ -116,6 +116,8 @@ def __init__(self, loop_type="", **kwargs):
             self.variable = ischedule.symbol_table.find_or_create_tag(
                 tag, root_name=suggested_name, symbol_type=DataSymbol,
                 datatype=LFRicTypes("LFRicIntegerScalarDataType")())
+        else:
+            self.variable = DataSymbol("null", ScalarType.integer_type())
 
         # The loop bounds names are given by the number of previous LFRic loops
         # already present in the Schedule. Since this are inserted in order it
@@ -185,11 +187,11 @@ def lower_to_language_level(self):
                 child.lower_to_language_level()
 
             # Finally create the new lowered Loop and replace the domain one
-            loop = Loop.create(self._variable, start, stop, step, [])
+            loop = Loop.create(self.variable, start, stop, step, [])
             loop.preceding_comment = self.preceding_comment
             loop.loop_body._symbol_table = \
                 self.loop_body.symbol_table.shallow_copy()
-            loop.children[3] = self.loop_body.copy()
+            loop.children[4] = self.loop_body.copy()
             self.replace_with(loop)
             lowered_node = loop
         else:
@@ -1104,6 +1106,32 @@ def independent_iterations(self,
         raise InternalError(f"independent_iterations: loop of type "
                             f"'{self.loop_type}' is not supported.")
 
+    def reference_accesses(self) -> VariablesAccessMap:
+        '''
+        :returns: a map of all the symbol accessed inside this node, the
+            keys are Signatures (unique identifiers to a symbol and its
+            structure accessors) and the values are AccessSequence
+            (a sequence of AccessTypes).
+
+        '''
+        var_accesses = VariablesAccessMap()
+
+        if self.variable.name != "null":
+            var_accesses.add_access(Signature(self.variable.name),
+                                    AccessType.WRITE, self)
+            # This re
+            var_accesses.add_access(Signature(self.variable.name),
+                                    AccessType.READ, self)
+            var_accesses.update(self.start_expr.reference_accesses())
+            var_accesses.update(self.stop_expr.reference_accesses())
+            var_accesses.update(self.step_expr.reference_accesses())
+
+        # LFRic loops ignore the loop variable reference and loop bounds
+        # because it has placeholders until the DSL loop is lowered.
+        for child in self.loop_body.children:
+            var_accesses.update(child.reference_accesses())
+        return var_accesses
+
 
 # ---------- Documentation utils -------------------------------------------- #
 # The list of module members that we wish AutoAPI to generate

src/psyclone/domain/lfric/lfric_loop_bounds.py

@@ -78,7 +78,7 @@ def initialise(self, cursor: int) -> int:
             assignment = Assignment.create(
                     lhs=Reference(lbound),
                     rhs=loop.lower_bound_psyir())
-            loop.children[0] = Reference(lbound)
+            loop.start_expr = Reference(lbound)
             self._invoke.schedule.addchild(assignment, cursor)
             cursor += 1
             if first:
@@ -99,10 +99,10 @@ def initialise(self, cursor: int) -> int:
                         rhs=loop.upper_bound_psyir()
                     ), cursor)
                 cursor += 1
-                loop.children[1] = Reference(ubound)
+                loop.stop_expr = Reference(ubound)
             else:
                 # If it needs a color look-up, it has to be in-place
-                loop.children[1] = loop.upper_bound_psyir()
+                loop.stop_expr = loop.upper_bound_psyir()
 
         return cursor
 

src/psyclone/psyad/adjoint_visitor.py

@@ -361,7 +361,7 @@ def loop_node(self, node):
         new_node.step_expr = negate_expr(new_node.step_expr.copy())
 
         # Determine the adjoint of the loop body
-        new_node.children[3] = self._visit(node.children[3])
+        new_node.children[4] = self._visit(node.loop_body)
         return new_node
 
     def ifblock_node(self, node):

src/psyclone/psyir/nodes/directive.py

@@ -101,12 +101,17 @@ def create_data_movement_deep_copy_refs(self):
         for sig in var_info.all_signatures:
             vinfo = var_info[sig]
             node = vinfo[0].node
-            sym = table.lookup(sig.var_name)
+
+            sym = table.lookup(sig.var_name, otherwise=None)
 
             if not vinfo.has_data_access():
                 # Ignore references that don't correspond to data accesses.
                 continue
 
+            if not sym:
+                # Ignore signatures without a corresponding symbol
+                continue
+
             if isinstance(sym.datatype, ScalarType):
                 # We ignore scalars as these are typically copied by value.
                 continue

src/psyclone/psyir/nodes/dynamic_omp_task_directive.py

@@ -1830,7 +1830,7 @@ def _evaluate_loop(
         # Finished handling the loop bounds now
 
         # Recurse to the children
-        for child_node in node.children[3].children:
+        for child_node in node.loop_body.children:
             self._evaluate_node(
                 child_node,
                 clause_lists