Arm backend: Add linear decomposition

backends/arm/_passes/arm_pass_manager.py

@@ -23,6 +23,7 @@
 from executorch.backends.arm._passes.decompose_layernorm_pass import (
     DecomposeLayerNormPass,
 )
+from executorch.backends.arm._passes.decompose_linear_pass import DecomposeLinearPass
 from executorch.backends.arm._passes.decompose_meandim_pass import DecomposeMeanDimPass
 from executorch.backends.arm._passes.decompose_softmaxes_pass import (
     DecomposeSoftmaxesPass,
@@ -74,6 +75,7 @@ def transform_to_backend_pipeline(
         self.add_pass(ConvertSplitToSlicePass())
         self.add_pass(Conv1dUnsqueezePass(exported_program))
         self.add_pass(DecomposeSoftmaxesPass())
+        self.add_pass(DecomposeLinearPass())
         for spec in compile_spec:
             if spec.key == "permute_memory_format":
                 memory_format = spec.value.decode()

backends/arm/_passes/decompose_linear_pass.py

@@ -0,0 +1,112 @@
+# Copyright 2024 Arm Limited and/or its affiliates.
+# All rights reserved.
+#
+# This source code is licensed under the BSD-style license found in the
+# LICENSE file in the root directory of this source tree.
+
+import numpy as np
+from executorch.backends.arm._passes.arm_pass_utils import (
+    create_node,
+    get_first_fake_tensor,
+)
+from executorch.backends.arm.tosa_quant_utils import dq_op, q_op
+from executorch.exir.dialects._ops import ops as exir_ops
+from executorch.exir.pass_base import ExportPass, PassResult
+
+
+class DecomposeLinearPass(ExportPass):
+    """
+    This pass decomposes linear into a Conv2D with the required view operations.
+    linear(x, weights, bias) becomes:
+        x_reshaped       = view(x)
+        weights_reshaped = view(weights)
+        conv2d           = conv2d(x_reshaped, weights_reshaped, bias)
+        output           = view(conv2d)
+    It also inserts q/dq pairs if the linear node was quantized.
+    """
+
+    def call(self, graph_module):
+        for node in graph_module.graph.nodes:
+            if node.op != "call_function":
+                continue
+            if node.target != exir_ops.edge.aten.linear.default:
+                continue
+            args = node.args
+            input = args[0]
+            weights = args[1]
+            bias = args[2] if len(args) > 2 else None
+            output_shape = get_first_fake_tensor(node).shape
+            input_shape = get_first_fake_tensor(input).shape
+            weights_shape = get_first_fake_tensor(weights).shape
+            batches = int(np.prod(input_shape[:-1])) if len(input_shape) > 1 else 1
+            # input has shape (..., Ci)
+            input_reshaped_shape = [batches, input_shape[-1], 1, 1]
+            # weights have shape (Co, Ci)
+            weights_reshaped_shape = [weights_shape[0], weights_shape[1], 1, 1]
+
+            with graph_module.graph.inserting_before(node):
+                quantize = input.op == "call_function" and input.target == dq_op
+                q_params = input.args[1:] if quantize else None
+                # Reshape input to 4D with shape (N, Ci, 1, 1)
+                input_reshaped = create_node(
+                    graph=graph_module.graph,
+                    op_target=exir_ops.edge.aten.view_copy.default,
+                    args=(input, input_reshaped_shape),
+                    kwargs={},
+                    quantize=quantize,
+                    q_params=q_params,
+                )
+
+                quantize = weights.op == "call_function" and weights.target == dq_op
+                q_params = weights.args[1:] if quantize else None
+                # Reshape weights to 4D with shape (Co, Ci, 1, 1)
+                weights_reshaped = create_node(
+                    graph=graph_module.graph,
+                    op_target=exir_ops.edge.aten.view_copy.default,
+                    args=(weights, weights_reshaped_shape),
+                    kwargs={},
+                    quantize=quantize,
+                    q_params=q_params,
+                )
+
+                consumer_node = list(node.users)[0]
+                quantize = (
+                    consumer_node.op == "call_function" and consumer_node.target == q_op
+                )
+                q_params = consumer_node.args[1:] if quantize else None
+                conv = create_node(
+                    graph=graph_module.graph,
+                    op_target=exir_ops.edge.aten.convolution.default,
+                    args=(
+                        input_reshaped,
+                        weights_reshaped,
+                        bias,
+                        [1, 1],  # strides
+                        [0, 0],  # padding
+                        [1, 1],  # dilation
+                        False,  # transposed
+                        [0, 0],  # output padding
+                        1,  # groups
+                    ),
+                    kwargs={},
+                    quantize=quantize,
+                    q_params=q_params,
+                )
+
+            with graph_module.graph.inserting_after(conv):
+                # Reshape output to same rank as original input with shape (..., Co)
+                # No need to insert q/dq pair as Conv2D node above has inserted them if
+                # required.
+                output = create_node(
+                    graph=graph_module.graph,
+                    op_target=exir_ops.edge.aten.view_copy.default,
+                    args=(conv, list(output_shape)),
+                    kwargs={},
+                )
+
+            node.replace_all_uses_with(output)
+            graph_module.graph.erase_node(node)
+            graph_module.graph.eliminate_dead_code()
+        graph_module.recompile()
+        graph_module = super().call(graph_module).graph_module
+        return PassResult(graph_module, True)

backends/arm/arm_partitioner.py

@@ -8,7 +8,7 @@
 import logging
 import operator
 import os
-from typing import cast, final, List
+from typing import Callable, cast, final, List, Optional, Tuple
 
 import torch
 from executorch.backends.arm.arm_backend import ArmBackend  # usort: skip
@@ -39,7 +39,6 @@ class TOSASupportedOperators(OperatorSupportBase):
     def is_node_supported(self, submodules, node: torch.fx.Node) -> bool:
         supported = node.op == "call_function" and node.target in [
             exir_ops.edge.aten.add.Tensor,
-            exir_ops.edge.aten.addmm.default,
             exir_ops.edge.aten.expand_copy.default,
             exir_ops.edge.aten.cat.default,
             exir_ops.edge.aten.bmm.default,
@@ -49,6 +48,7 @@ def is_node_supported(self, submodules, node: torch.fx.Node) -> bool:
             exir_ops.edge.aten.div.Tensor,
             exir_ops.edge.aten.exp.default,
             exir_ops.edge.aten.log.default,
+            exir_ops.edge.aten.linear.default,
             exir_ops.edge.aten.split_with_sizes_copy.default,
             exir_ops.edge.aten.full.default,
             exir_ops.edge.aten.mul.Tensor,
@@ -137,3 +137,12 @@ def partition(self, exported_program: ExportedProgram) -> PartitionResult:
         return PartitionResult(
             tagged_exported_program=exported_program, partition_tags=partition_tags
         )
+
+    def ops_to_not_decompose(
+        self,
+        ep: ExportedProgram,
+    ) -> Tuple[List[torch._ops.OpOverload], Optional[Callable[[torch.fx.Node], bool]]]:
+        ops_to_not_decompose = [
+            torch.ops.aten.linear.default,
+        ]
+        return (ops_to_not_decompose, None)

backends/arm/operators/__init__.py

@@ -8,7 +8,6 @@
 from . import (  # noqa
     node_visitor,
     op_add,
-    op_addmm,
     op_avg_pool2d,
     op_batch_norm,
     op_bmm,

backends/arm/operators/op_add.py

@@ -62,10 +62,8 @@ def define_node(
                 input_nodes, tosa_graph
             )
 
-            # Preapre sub output tensor
-            broadcasted_shape = tutils.broadcast_shapes(
-                rescaled_inputs[0].shape, rescaled_inputs[0].shape
-            )
+            # Prepare add output tensor
+            broadcasted_shape = tutils.tosa_shape(output.shape, output.dim_order)
             add_output = tosa_graph.addIntermediate(broadcasted_shape, ts.DType.INT32)
         else:
             add_output = output

backends/arm/operators/op_permute.py

@@ -14,7 +14,6 @@
     register_node_visitor,
 )
 from executorch.backends.arm.tosa_mapping import TosaArg
-from executorch.backends.arm.tosa_utils import is_permute_node_before_addmm
 from serializer.tosa_serializer import TosaOp
 
 
@@ -81,13 +80,6 @@ def define_node(
         output: TosaArg,
         is_quant_node: bool,
     ) -> None:
-        if is_permute_node_before_addmm(node):
-            ## Simply add an identityOp
-            tosa_graph.addOperator(
-                TosaOp.Op().IDENTITY, [inputs[0].name], [output.name]
-            )
-            return
-
         # The permutation vector describes a permutation P in default Pytorch dim_order.
         # For rank 4, the default dim_order NCHW.
         # E.g. (2,3,0,1) -> permute (n,c,h,w) to (w,c,n,h)