fixed the issue in definition use chains when we find empty scopes

src/psyclone/psyir/tools/definition_use_chains.py

@@ -250,16 +250,20 @@ def find_forward_accesses(self):
                         .abs_position
                         + 1
                     )
-                    # We make a copy of the reference to have a detached
-                    # node to avoid handling the special cases based on
-                    # the parents of the reference.
-                    chain = DefinitionUseChain(
-                        self._reference.copy(),
-                        body,
-                        start_point=ancestor.abs_position,
-                        stop_point=sub_stop_point,
-                    )
-                    chains.insert(0, chain)
+                    # If we have a basic block with no children then skip it,
+                    # e.g. for an if block with no code before the else
+                    # statement, as is found in NEMO4.
+                    if(len(body) > 0):
+                        # We make a copy of the reference to have a detached
+                        # node to avoid handling the special cases based on
+                        # the parents of the reference.
+                        chain = DefinitionUseChain(
+                            self._reference.copy(),
+                            body,
+                            start_point=ancestor.abs_position,
+                            stop_point=sub_stop_point,
+                        )
+                        chains.insert(0, chain)
                     # If its a while loop, create a basic block for the while
                     # condition.
                     if isinstance(ancestor, WhileLoop):
@@ -300,6 +304,11 @@ def find_forward_accesses(self):
             # Now add all the other standardly handled basic_blocks to the
             # list of chains.
             for block in basic_blocks:
+                # If we have a basic block with no children then skip it,
+                # e.g. for an if block with no code before the else
+                # statement, as is found in NEMO4.
+                if(len(block) == 0):
+                    continue
                 chain = DefinitionUseChain(
                     self._reference,
                     block,
@@ -835,6 +844,11 @@ def find_backward_accesses(self):
             # Now add all the other standardly handled basic_blocks to the
             # list of chains.
             for block in basic_blocks:
+                # If we have a basic block with no children then skip it,
+                # e.g. for an if block with no code before the else
+                # statement, as is found in NEMO4.
+                if(len(block) == 0):
+                    continue
                 chain = DefinitionUseChain(
                     self._reference,
                     block,
@@ -874,14 +888,18 @@ def find_backward_accesses(self):
                         ).abs_position
                     else:
                         sub_start_point = self._reference.abs_position
-                    chain = DefinitionUseChain(
-                        self._reference.copy(),
-                        body,
-                        start_point=sub_start_point,
-                        stop_point=sub_stop_point,
-                    )
-                    chains.append(chain)
-                    control_flow_nodes.append(ancestor)
+                    # If we have a basic block with no children then skip it,
+                    # e.g. for an if block with no code before the else
+                    # statement, as is found in NEMO4.
+                    if(len(body) > 0):
+                        chain = DefinitionUseChain(
+                            self._reference.copy(),
+                            body,
+                            start_point=sub_start_point,
+                            stop_point=sub_stop_point,
+                        )
+                        chains.append(chain)
+                        control_flow_nodes.append(ancestor)
                     # If its a while loop, create a basic block for the while
                     # condition.
                     if isinstance(ancestor, WhileLoop):

src/psyclone/tests/psyir/tools/definition_use_chains_backward_dependence_test.py

@@ -687,3 +687,33 @@ def test_definition_use_chains_backward_accesses_nonassign_reference_in_loop(
     assert reaches[0] is routine.children[1].loop_body.children[1].children[1]
     assert reaches[1] is routine.children[1].loop_body.children[0].lhs
     assert reaches[2] is routine.children[0].lhs
+
+def test_definition_use_chains_backward_accesses_empty_schedules(
+    fortran_reader,
+):
+    '''Coverage to handle the case where we have empty schedules inside
+    various type of code.'''
+    code = """
+    subroutine x()
+    integer :: a, i
+    a = 1
+    do i = 1, 100
+    end do
+    if(.TRUE.) then
+    else
+    endif
+    do while(.FALSE.)
+    end do
+    a = a + a
+    end subroutine x
+    """
+    psyir = fortran_reader.psyir_from_source(code)
+    routine = psyir.walk(Routine)[0]
+    chains = DefinitionUseChain(
+            routine.children[4].lhs
+    )
+    reaches = chains.find_backward_accesses()
+    assert len(reaches) == 3
+    assert reaches[0] is routine.children[4].rhs.children[1]
+    assert reaches[1] is routine.children[4].rhs.children[0]
+    assert reaches[2] is routine.children[0].lhs

src/psyclone/tests/psyir/tools/definition_use_chains_forward_dependence_test.py

@@ -937,3 +937,33 @@ def test_definition_use_chains_forward_accesses_multiple_routines(
     )
     reaches = chains.find_forward_accesses()
     assert len(reaches) == 0
+
+def test_definition_use_chains_forward_accesses_empty_schedules(
+    fortran_reader,
+):
+    '''Coverage to handle the case where we have empty schedules inside
+    various type of code.'''
+    code = """
+    subroutine x()
+    integer :: a, i
+    a = 1
+    do i = 1, 100
+    end do
+    if(.TRUE.) then
+    else
+    endif
+    do while(.FALSE.)
+    end do
+    a = a + a
+    end subroutine x
+    """
+    psyir = fortran_reader.psyir_from_source(code)
+    routine = psyir.walk(Routine)[0]
+    chains = DefinitionUseChain(
+            routine.children[0].lhs
+    )
+    reaches = chains.find_forward_accesses()
+    assert len(reaches) == 3
+    assert reaches[0] is routine.children[4].rhs.children[0]
+    assert reaches[1] is routine.children[4].rhs.children[1]
+    assert reaches[2] is routine.children[4].lhs