Pattern-Matching and Subgraph Transformations¶
In DaCe, the easiest way to locally modify an SDFG is by data-centric transformations. Transformations are a powerful tool to optimize applications in DaCe. You can go from naive code to state-of-the-art performance using only transformations.
All transformations extend the
TransformationBase class. There are three built-in types of transformations in DaCe:
Pattern-matching Transformations (extending
PatternTransformation): Transformations that require a certain subgraph structure to match. Within this abstract class, there are two sub-classes:
A pattern-matching must extend at least one of those two classes.
Subgraph Transformations (extending
SubgraphTransformation): Transformations that can operate on arbitrary subgraphs.
Another form of (implicit) transformation is a Library node expansion (extending
ExpandTransformation). It is a class used for tracking when library nodes are expanded, and creating a library node implementation involves extending this class.
Transformations can have properties and those can be used when applying them: for example, tile sizes in
For more information on how to use and author data-centric transformations, see the Using and Creating Transformations tutorial.
A pattern-matching transformation works on a specific subgraph pattern, and, using the API, can be used to find all
instances of that pattern and apply it anywhere.
Authoring such a transformation requires extending one of the two subclasses mentioned above
MultiStateTransformation), add static
PatternNode fields to the class to
represent the pattern, and implement at least three methods:
expressions: A method that returns a list of graph patterns that match this transformation.
can_be_applied: A method that, given a subgraph candidate, checks for additional conditions whether it can be transformed.
apply: A method that applies the transformation on the given SDFG.
An instance of the transformation class is associated with a specific match, so using the fields in the class relate to a specific subgraph.
For example, the following sample transformation matches an access node connected to a map entry, and changes the map’s label to match the name of that access node:
from dace.sdfg import nodes, SDFG, SDFGState from dace.sdfg.utils import node_path_graph from dace.transformation import transformation as xf class MyTransformation(xf.SingleStateTransformation): # Pattern nodes are defined here and can be used in the class access = xf.PatternNode(nodes.AccessNode) map_node = xf.PatternNode(nodes.MapEntry) @classmethod def expressions(cls): # The pattern to match is ``access -> map_node``. Since this is a # class method, accessing ``cls.access`` gets the pattern node. return [node_path_graph(cls.access, cls.map_node)] # Because this is a Single-State Transformation, the first argument here # is ``state`` def can_be_applied(self, state: SDFGState, expr_index: int, sdfg: SDFG, permissive=False) -> bool: # We can now use ``self.access``, which refers to a specific subgraph # pattern match if self.access.data == 'mydata': return True # We only match patterns in which the access node is accessing 'mydata' return False def apply(self, state: SDFGState, sdfg: SDFG) -> nodes.MapEntry: # Here we apply the transformation, and can return any object. This # is sometimes used when transformations are composed together and # need to pass information to each other. self.map_node.label = 'mymap' return self.map_node
Subgraph transformations can be applied to any subgraph that returns True for the
can_be_applied method. It is used
when arbitrary local regions need to be modified, e.g., in
SubgraphFusion. The implementation is very similar to
pattern-matching transformations, but without the pattern. A simple example with a property would be:
from dace.sdfg import nodes, SDFG from dace.sdfg.utils import node_path_graph from dace.transformation import transformation as xf from dace.sdfg.graph import SubgraphView from dace.properties import make_properties, Property @make_properties class ExampleSubgraphXform(xf.SubgraphTransformation): """ This string describes the transformation and will be shown in the Visual Studio Code plugin. """ # Properties can be defined on Transformation classes as with other objects simplify = Property(desc="Simplify SDFG after applying transformation.", dtype=bool, default=False) def can_be_applied(self, sdfg: SDFG, subgraph: SubgraphView) -> bool: return True def apply(self, sdfg: SDFG) -> None: # First we obtain the subgraph view from the SDFG we matched in subgraph = self.subgraph_view(sdfg) # Then we can work on the graph normally for node in subgraph.nodes(): # Do something complex... pass if self.simplify: sdfg.simplify()