Remove legacy optimizer (#2180)

- Remove legacy optimizer and support proto inputs with the IR based
optimizer.
- Add a new `inline=True` option in `optimize()` to control whether
function inlining is done when optimizing
- Implement identity folding for graph outputs
- Migrate constant folding tests to run on IR models

Fix #2185

---------

Co-authored-by: Ganesan Ramalingam <grama@microsoft.com>

Author: justinchuby

onnxscript/optimizer/__init__.py

@@ -2,37 +2,90 @@
 # Licensed under the MIT License.
 from __future__ import annotations
 
+from typing import TypeVar
+
 __all__ = [
-    "fold_constants",
-    "fold_constants_ir",
-    "remove_unused_nodes",
-    "optimize",
-    "optimize_ir",
     "basic_constant_propagation",
+    "fold_constants_ir",
+    "fold_constants",
     "inline",
+    "optimize_ir",
+    "optimize",
+    "remove_unused_nodes",
 ]
 
 import onnx
 
 import onnxscript.ir.passes.common.inliner
 import onnxscript.ir.passes.common.unused_removal
 import onnxscript.optimizer._constant_folding as constant_folding
-import onnxscript.optimizer._legacy._optimizer as legacy_optimizer
-import onnxscript.optimizer._legacy.constant_folding as legacy_constant_folding
 from onnxscript import ir
+from onnxscript.optimizer._constant_folding import (
+    basic_constant_propagation,
+)
+from onnxscript.optimizer._constant_folding import (
+    fold_constants as fold_constants_ir,
+)
 from onnxscript.optimizer._optimizer import optimize_ir
 
-basic_constant_propagation = constant_folding.basic_constant_propagation
-fold_constants_ir = constant_folding.fold_constants
+_ModelProtoOrIr = TypeVar("_ModelProtoOrIr", onnx.ModelProto, ir.Model)
+
 
+def optimize(
+    model: _ModelProtoOrIr,
+    num_iterations: int = 2,
+    *,
+    onnx_shape_inference: bool = True,
+    stop_if_no_change: bool = True,
+    input_size_limit: int = constant_folding.DEFAULT_CONSTANT_FOLD_INPUT_SIZE_LIMIT,
+    output_size_limit: int = constant_folding.DEFAULT_CONSTANT_FOLD_OUTPUT_SIZE_LIMIT,
+    inline: bool = True,
+) -> _ModelProtoOrIr:
+    """Optimizes a model.
 
-def optimize(model: ir.Model, *args, **kwargs) -> ir.Model:
+    Args:
+        model: The model to be optimized.
+        num_iterations: Number of times the optimization loop is repeated.
+        onnx_shape_inference: Applies node-level shape-inference as part of optimization
+        input_size_limit: Will not apply constant folding to ops with any input of size
+            greater than this. Does not apply to special ops like Shape() and Size().
+        output_size_limit: Will not rewrite any foldable-op into a Constant op if the size
+            of the output tensor is greater than this.
+        stop_if_no_change: Stop the optimization loop if no change is detected in an iteration.
+        inline: If True, inlines all functions in the model.
+
+    Returns:
+        The optimized model. If the input was a ModelProto, the output will also be a
+        ModelProto. If the input was an ir.Model, the output will also be an ir.Model.
+    """
     if isinstance(model, ir.Model):
-        # In that case, this is done inplace.
-        optimize_ir(model, *args, **kwargs)
+        # In this case, optimize is done inplace.
+        # TODO(justinchuby): Maybe make functional
+        optimize_ir(
+            model,
+            num_iterations=num_iterations,
+            onnx_shape_inference=onnx_shape_inference,
+            stop_if_no_change=stop_if_no_change,
+            input_size_limit=input_size_limit,
+            output_size_limit=output_size_limit,
+            inline=inline,
+        )
         return model
     else:
-        return legacy_optimizer.optimize(model, *args, **kwargs)
+        assert isinstance(model, onnx.ModelProto)
+        model_ir = ir.serde.deserialize_model(model)
+        optimize_ir(
+            model_ir,
+            num_iterations=num_iterations,
+            onnx_shape_inference=onnx_shape_inference,
+            stop_if_no_change=stop_if_no_change,
+            input_size_limit=input_size_limit,
+            output_size_limit=output_size_limit,
+            inline=inline,
+        )
+        # Move the model back to the proto
+        new_proto = ir.serde.serialize_model(model_ir)
+        return new_proto
 
 
 def inline(model: ir.Model) -> None:
@@ -43,11 +96,20 @@ def inline(model: ir.Model) -> None:
 
 def fold_constants(
     model: ir.Model | onnx.ModelProto, *args, **kwargs
-) -> constant_folding.FoldConstantsResult | bool:
+) -> constant_folding.FoldConstantsResult:
+    """Fold constants in a model in place."""
     if isinstance(model, ir.Model):
         return constant_folding.fold_constants(model, *args, **kwargs)
     else:
-        return legacy_constant_folding.fold_constants(model, *args, **kwargs)
+        assert isinstance(model, onnx.ModelProto)
+        model_proto = model
+        model = ir.serde.deserialize_model(model_proto)
+        result = constant_folding.fold_constants(model, *args, **kwargs)
+        # Move the model back to the proto
+        new_proto = ir.serde.serialize_model(model)
+        model_proto.Clear()
+        model_proto.CopyFrom(new_proto)
+        return result
 
 
 def remove_unused_nodes(model: ir.Model | onnx.ModelProto) -> None:

onnxscript/optimizer/_constant_folding.py

@@ -919,7 +919,7 @@ def get_type(value: ir.Value) -> onnx.TypeProto | None:
                     e,
                 )
 
-    def new_constant(self, node: ir.Node, value):
+    def new_constant(self, node: ir.Node, value) -> ir.Node | None:
         irvalue = node.outputs[0]
         if not isinstance(value, np.ndarray):
             # ONNX does not have a way to represent non-tensor constants, eg. a sequence.
@@ -965,7 +965,7 @@ def new_constant(self, node: ir.Node, value):
         node = ir.Node("", "Constant", inputs=[], attributes=attributes, num_outputs=1)
         return node
 
-    def process_node(self, node: ir.Node):
+    def process_node(self, node: ir.Node) -> Replacement | None:
         for i, value in enumerate(node.inputs):
             sym_value = self._state.get_sym_value(value)
             if isinstance(sym_value, ir.Value):
@@ -1046,7 +1046,7 @@ def convert(av):
             )
         return None
 
-    def replace_node(self, node: ir.Node, replacement, root: ir.Graph | ir.Function):
+    def replace_node(self, node: ir.Node, replacement, root: ir.Graph | ir.Function) -> None:
         logger.debug("Replacing node: %s::%s %s", node.domain, node.op_type, node.name)
 
         ir.convenience.replace_nodes_and_values(
@@ -1066,13 +1066,13 @@ def visit_attribute(self, attr: ir.Attr | ir.RefAttr) -> None:
                 for graph in attr.as_graphs():
                     self.visit_graph(graph)
 
-    def visit_node(self, node: ir.Node, root: ir.Graph | ir.Function):
+    def visit_node(self, node: ir.Node, root: ir.Graph | ir.Function) -> None:
         replacement = self.process_node(node)
         if replacement is None:
             # No change. Process attributes.
             for attr in node.attributes.values():
                 self.visit_attribute(attr)
-            return None
+            return
         else:
             self.replace_node(node, replacement, root)
 
@@ -1087,6 +1087,22 @@ def visit_graph(self, graph: ir.Graph) -> None:
         for node in graph:
             self.visit_node(node, graph)
 
+        # Replace outputs if output nodes can be folded. This are typically outputs from
+        # Identity nodes
+        for i, output in enumerate(graph.outputs):
+            if output is None:
+                continue
+            sym_value = self._state.get_sym_value(output)
+            if not isinstance(sym_value, ir.Value):
+                # An output must be a Value
+                continue
+            if not _sym_value_can_replace_graph_output(graph, sym_value, output):
+                continue
+            # Rename sym_value to match the output name
+            sym_value.name = output.name
+            graph.outputs[i] = sym_value
+            self.modified = True
+
         self._state.pop_initializer_inputs()
 
     def visit_function(self, function: ir.Function) -> None:
@@ -1103,6 +1119,24 @@ def call(self, model: ir.Model) -> ir.passes.PassResult:
         return FoldConstantsResult(model, self.modified, self._state.symbolic_value_map)
 
 
+def _sym_value_can_replace_graph_output(
+    graph: ir.Graph, sym_value: ir.Value, output: ir.Value
+) -> bool:
+    if (producer := sym_value.producer()) is None:
+        # If the sym_value has no producer, it is some graph's input
+        # ONNX does not allow a graph input to be a graph output
+        return False
+    if producer.graph is not graph:
+        # The sym_value must be produced by a node in the graph to be an output of this graph
+        return False
+    if sym_value.is_graph_output():
+        # If the sym_value is already an output of a graph, we cannot rename it
+        # to this output name. Otherwise the graph output represented by sym_value
+        # will lose its name.
+        return False
+    return True
+
+
 @dataclasses.dataclass
 class FoldConstantsResult(ir.passes.PassResult):
     symbolic_value_map: dict[ir.Value, SymbolicValue]