Source code for torch.fx.interpreter
from .graph_module import GraphModule
from .graph import Graph
from .node import Argument, Node, Target, map_arg
from .proxy import Proxy
from .symbolic_trace import Tracer
from typing import Any, Dict, Iterator, Optional, Tuple
[docs]class Interpreter:
"""
An Interpreter executes an FX graph Node-by-Node. This pattern
can be useful for many things, including writing code
transformations as well as analysis passes.
Methods in the Interpreter class can be overridden to customize
the behavior of execution. The map of overrideable methods
in terms of call hierarchy::
run()
+-- run_node
+-- placeholder()
+-- get_attr()
+-- call_function()
+-- call_method()
+-- call_module()
+-- output()
Example:
Suppose we want to swap all instances of ``torch.neg`` with
``torch.sigmoid`` and vice versa (including their ``Tensor``
method equivalents). We could subclass Interpreter like so::
class NegSigmSwapInterpreter(Interpreter):
def call_function(self, target : Target,
args : Tuple, kwargs : Dict) -> Any:
if target == torch.sigmoid:
return torch.neg(*args, **kwargs)
return super().call_function(n)
def call_method(self, target : Target,
args : Tuple, kwargs : Dict) -> Any:
if target == 'neg':
call_self, *args_tail = args
return call_self.sigmoid(*args_tail, **kwargs)
return super().call_method(n)
def fn(x):
return torch.sigmoid(x).neg()
gm = torch.fx.symbolic_trace(fn)
input = torch.randn(3, 4)
result = NegSigmSwapInterpreter(gm).run(input)
torch.testing.assert_allclose(result, torch.neg(input).sigmoid())
Args:
module (GraphModule): The module to be executed
"""
def __init__(self, module : GraphModule):
assert isinstance(module, GraphModule)
self.module = module
self.submodules = dict(self.module.named_modules())
self.env : Dict[Node, Any] = {}
[docs] def run(self, *args, initial_env : Optional[Dict[Node, Any]] = None) -> Any:
"""
Run `module` via interpretation and return the result.
Args:
*args: The arguments to the Module to run, in positional order
initial_env (Optional[Dict[Node, Any]]): An optional starting environment for execution.
This is a dict mapping `Node` to any value. This can be used, for example, to
pre-populate results for certain `Nodes` so as to do only partial evaluation within
the interpreter.
Returns:
Any: The value returned from executing the Module
"""
self.env = initial_env if initial_env else {}
# Positional function args are consumed left-to-right by
# `placeholder` nodes. Use an iterator to keep track of
# position and extract those values.
self.args_iter : Iterator[Any] = iter(args)
for node in self.module.graph.nodes:
if node in self.env:
# Short circuit if we have this value. This could
# be used, for example, for partial evaluation
# where the caller has pre-populated `env` with
# values for a subset of the program.
continue
self.env[node] = self.run_node(node)
if node.op == 'output':
output_val = self.env[node]
return output_val
[docs] def run_node(self, n : Node) -> Any:
"""
Run a specific node ``n`` and return the result.
Calls into placeholder, get_attr, call_function,
call_method, call_module, or output depending
on ``node.op``
Args:
n (Node): The Node to execute
Returns:
Any: The result of executing ``n``
"""
args, kwargs = self.fetch_args_kwargs_from_env(n)
assert isinstance(args, tuple)
assert isinstance(kwargs, dict)
return getattr(self, n.op)(n.target, args, kwargs)
# Main Node running APIs
[docs] def placeholder(self, target : 'Target', args : Tuple[Any], kwargs : Dict[str, Any]) -> Any:
"""
Execute a ``placeholder`` node. Note that this is stateful:
``Interpreter`` maintains an internal iterator over
arguments passed to ``run`` and this method returns
next() on that iterator.
Args:
target (Target): The call target for this node. See
`Node <https://pytorch.org/docs/master/fx.html#torch.fx.Node>`__ for
details on semantics
args (Tuple): Tuple of positional args for this invocation
kwargs (Dict): Dict of keyword arguments for this invocation
Returns:
Any: The argument value that was retrieved.
"""
assert isinstance(target, str)
if target.startswith('*'):
# For a starred parameter e.g. `*args`, retrieve all
# remaining values from the args list.
return list(self.args_iter)
else:
return next(self.args_iter)
[docs] def get_attr(self, target : 'Target', args : Tuple[Any], kwargs : Dict[str, Any]) -> Any:
"""
Execute a ``get_attr`` node. Will retrieve an attribute
value from the ``Module`` hierarchy of ``self.module``.
Args:
target (Target): The call target for this node. See
`Node <https://pytorch.org/docs/master/fx.html#torch.fx.Node>`__ for
details on semantics
args (Tuple): Tuple of positional args for this invocation
kwargs (Dict): Dict of keyword arguments for this invocation
Return:
Any: The value of the attribute that was retrieved
"""
assert isinstance(target, str)
return self.fetch_attr(target)
[docs] def call_function(self, target : 'Target', args : Tuple[Any], kwargs : Dict[str, Any]) -> Any:
"""
Execute a ``call_function`` node and return the result.
Args:
target (Target): The call target for this node. See
`Node <https://pytorch.org/docs/master/fx.html#torch.fx.Node>`__ for
details on semantics
args (Tuple): Tuple of positional args for this invocation
kwargs (Dict): Dict of keyword arguments for this invocation
Return
Any: The value returned by the function invocation
"""
assert not isinstance(target, str)
# Execute the function and return the result
return target(*args, **kwargs)
[docs] def call_method(self, target : 'Target', args : Tuple[Any], kwargs : Dict[str, Any]) -> Any:
"""
Execute a ``call_method`` node and return the result.
Args:
target (Target): The call target for this node. See
`Node <https://pytorch.org/docs/master/fx.html#torch.fx.Node>`__ for
details on semantics
args (Tuple): Tuple of positional args for this invocation
kwargs (Dict): Dict of keyword arguments for this invocation
Return
Any: The value returned by the method invocation
"""
# args[0] is the `self` object for this method call
self_obj, *args_tail = args # type: ignore
# Execute the method and return the result
assert isinstance(target, str)
return getattr(self_obj, target)(*args_tail, **kwargs)
[docs] def call_module(self, target : 'Target', args : Tuple[Any], kwargs : Dict[str, Any]) -> Any:
"""
Execute a ``call_module`` node and return the result.
Args:
target (Target): The call target for this node. See
`Node <https://pytorch.org/docs/master/fx.html#torch.fx.Node>`__ for
details on semantics
args (Tuple): Tuple of positional args for this invocation
kwargs (Dict): Dict of keyword arguments for this invocation
Return
Any: The value returned by the module invocation
"""
# Retrieve executed args and kwargs values from the environment
# Execute the method and return the result
assert isinstance(target, str)
submod = self.fetch_attr(target)
return submod(*args, **kwargs)
[docs] def output(self, target : 'Target', args : Tuple[Any], kwargs : Dict[str, Any]) -> Any:
"""
Execute an ``output`` node. This really just retrieves
the value referenced by the ``output`` node and returns it.
Args:
target (Target): The call target for this node. See
`Node <https://pytorch.org/docs/master/fx.html#torch.fx.Node>`__ for
details on semantics
args (Tuple): Tuple of positional args for this invocation
kwargs (Dict): Dict of keyword arguments for this invocation
Return:
Any: The return value referenced by the output node
"""
return args[0]
# Helper methods
[docs] def fetch_attr(self, target : str):
"""
Fetch an attribute from the ``Module`` hierarchy of ``self.module``.
Args:
target (str): The fully-qualfiied name of the attribute to fetch
Return:
Any: The value of the attribute.
"""
target_atoms = target.split('.')
attr_itr = self.module
for i, atom in enumerate(target_atoms):
if not hasattr(attr_itr, atom):
raise RuntimeError(f"Node referenced nonexistent target {'.'.join(target_atoms[:i])}")
attr_itr = getattr(attr_itr, atom)
return attr_itr
[docs] def fetch_args_kwargs_from_env(self, n : Node) -> Tuple[Tuple, Dict]:
"""
Fetch the concrete values of ``args`` and ``kwargs`` of node ``n``
from the current execution environment.
Args:
n (Node): The node for which ``args`` and ``kwargs`` should be fetched.
Return:
Tuple[Tuple, Dict]: ``args`` and ``kwargs`` with concrete values for ``n``.
"""
args = self.map_nodes_to_values(n.args, n)
assert isinstance(args, tuple)
kwargs = self.map_nodes_to_values(n.kwargs, n)
assert isinstance(kwargs, dict)
return args, kwargs
[docs] def map_nodes_to_values(self, args : Argument, n : Node) -> Argument:
"""
Recursively descend through ``args`` and look up the concrete value
for each ``Node`` in the current execution environment.
Args:
args (Argument): Data structure within which to look up concrete values
n (Node): Node to which ``args`` belongs. This is only used for error reporting.
"""
def load_arg(n_arg : Node) -> Any:
if n_arg not in self.env:
raise RuntimeError(f'Node {n} referenced nonexistent value {n_arg}! Run Graph.lint() '
f'to diagnose such issues')
return self.env[n_arg]
return map_arg(args, load_arg)
[docs]class Transformer(Interpreter):
"""
``Transformer`` is a special type of interpreter that produces a
new ``Module``. It exposes a ``transform()`` method that returns
the transformed ``Module``. ``Transformer`` does not require
arguments to run, as ``Interpreter`` does. ``Transformer`` works
entirely symbolically.
Example:
Suppose we want to swap all instances of ``torch.neg`` with
``torch.sigmoid`` and vice versa (including their ``Tensor``
method equivalents). We could subclass ``Transformer`` like so::
class NegSigmSwapXformer(Transformer):
def call_function(self, target : 'Target', args : Tuple[Any], kwargs : Dict[str, Any]) -> Any:
if target == torch.sigmoid:
return torch.neg(*args, **kwargs)
return super().call_function(n)
def call_method(self, target : 'Target', args : Tuple[Any], kwargs : Dict[str, Any]) -> Any:
if target == 'neg':
call_self, *args_tail = args
return call_self.sigmoid(*args_tail, **kwargs)
return super().call_method(n)
def fn(x):
return torch.sigmoid(x).neg()
gm = torch.fx.symbolic_trace(fn)
transformed : torch.nn.Module = NegSigmSwapXformer(gm).transform()
input = torch.randn(3, 4)
torch.testing.assert_allclose(transformed(input), torch.neg(input).sigmoid())
Args:
module (GraphModule): The ``Module`` to be transformed.
"""
def __init__(self, module):
super().__init__(module)
self.new_graph = Graph()
class TransformerTracer(Tracer):
def __init__(self, graph: Graph):
super().__init__()
self.graph = graph
def is_leaf_module(self, _, __) -> bool:
return True
self.tracer = TransformerTracer(self.new_graph)
self.tracer.root = module
[docs] def placeholder(self, target : 'Target', args : Tuple[Any], kwargs : Dict[str, Any]) -> Proxy:
"""
Execute a ``placeholder`` node. In ``Transformer``, this is
overridden to insert a new ``placeholder`` into the output
graph.
Args:
target (Target): The call target for this node. See
`Node <https://pytorch.org/docs/master/fx.html#torch.fx.Node>`__ for
details on semantics
args (Tuple): Tuple of positional args for this invocation
kwargs (Dict): Dict of keyword arguments for this invocation
"""
assert isinstance(target, str)
return Proxy(self.new_graph.placeholder(target), self.tracer)
[docs] def get_attr(self, target : 'Target', args : Tuple[Any], kwargs : Dict[str, Any]) -> Proxy:
"""
Execute a ``get_attr`` node. In ``Transformer``, this is
overridden to insert a new ``get_attr`` node into the output
graph.
Args:
target (Target): The call target for this node. See
`Node <https://pytorch.org/docs/master/fx.html#torch.fx.Node>`__ for
details on semantics
args (Tuple): Tuple of positional args for this invocation
kwargs (Dict): Dict of keyword arguments for this invocation
"""
assert isinstance(target, str)
return Proxy(self.new_graph.get_attr(target), self.tracer)
[docs] def transform(self) -> GraphModule:
"""
Transform ``self.module`` and return the transformed
``GraphModule``.
"""
result = super().run()
if result is not None:
assert isinstance(result, Proxy)
self.new_graph.output(result.node)
return GraphModule(self.module, self.new_graph)
