def is_loop_invariant(self, node, loop_node):
node_dependency_set = self.get_node_dependencies(node)
# print "is loop invariant node:", node
# for x in node_dependency_set:
# print " dep:", x
# find dependencies within the loop node but outside the node we're checking
node_dependency_set_except_node_tree = node_dependency_set - set(flatten_tree(node))
dependencies_within_loop = set(flatten_tree(loop_node)).intersection(
node_dependency_set_except_node_tree)
depends_on_loop_variants = bool(loop_node.loop_variant_set.intersection(
node_dependency_set))
# TODO: Disabling warnings for now. They are useless witout
# filenames. Also need to make sure all these cases are valid.
# if not depends_on_loop_variants and dependencies_within_loop:
# # we can't assume this is invariant because it depends on other
# # nodes inside the loop. eventually we should hoist out both the
# # node and its dependencies.
# dependency_nodes = '\n'.join(' %s' % node.parent for node in dependencies_within_loop)
# logging.warning("Cannot hoist possible loop invariant: %s.", node)
# logging.warning("Please move following dependencies out of the loop:\n%s",
# dependency_nodes)
return not depends_on_loop_variants and not dependencies_within_loop
def get_node_dependencies(self, node):
node_dependency_set = set(flatten_tree(node))
parent_block = self.get_parent_block(node)
for n in list(node_dependency_set):
# when this is an identifier, you need to check all of the potential
# the dependencies for that symbol, which means doing some crawling
if isinstance(n, IdentifierNode):
identifier = n
parent_block_to_check = parent_block
while parent_block_to_check:
for block_node in parent_block_to_check.child_nodes:
if isinstance(block_node, AssignNode):
if block_node.left == identifier:
node_dependency_set.update(
self.get_node_dependencies(block_node.right))
parent_block_to_check = None
break
elif isinstance(block_node, IfNode):
# if you encounter a conditional in your chain, you depend on any
# dependencies of the condition itself
# FIXME: calling get_node_dependencies(block_node.test_expression)
# causes an infinite loop, but that is probably the correct way
# forward to address the dependency chain
node_dependency_set.update(
flatten_tree(block_node.test_expression))
else:
parent_block_to_check = self.get_parent_block(
parent_block_to_check)
#elif isinstance(n, (GetUDNNode, FilterNode)):
# node_dependency_set.update(
# self.get_node_dependencies(node.expression))
#print "get_node_dependencies", node
#print " deps:", node_dependency_set
return node_dependency_set
def _get_identifiers_from_expression(node): """Find the IdentifierNodes present in an expression. This function searches through the nodes of an expression and returns a set of the IdentiferNodes that are present. This function doesn't traverse ast.GetAttrNode or any LiteralNodes such as ListLiteral or DictLiteral nodes. """ return set([n for n in walker.flatten_tree(node) if isinstance(n, ast.IdentifierNode)])
