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| 1 | +# Copyright 2025 Arm Limited and/or its affiliates. |
| 2 | +# |
| 3 | +# This source code is licensed under the BSD-style license found in the |
| 4 | +# LICENSE file in the root directory of this source tree. |
| 5 | + |
| 6 | +# pyre-unsafe |
| 7 | + |
| 8 | +import operator |
| 9 | + |
| 10 | +import torch |
| 11 | +from executorch.backends.arm._passes import ArmPass |
| 12 | +from executorch.backends.arm._passes.arm_pass_utils import create_node |
| 13 | +from executorch.exir.dialects._ops import ops as exir_ops |
| 14 | +from executorch.exir.pass_base import PassResult |
| 15 | + |
| 16 | + |
| 17 | +class DecomposeBatchNormNoStatsPass(ArmPass): |
| 18 | + """ |
| 19 | + Decompose BatchNorm2d(track_running_stats=False) (aten._native_batch_norm_legit_no_training) |
| 20 | + into a sequence of elementwise operations: |
| 21 | +
|
| 22 | + # let input = x, rm = running_mean, rv = running_var, eps: float |
| 23 | + rm_view = view(rm, weights_shape) |
| 24 | + rv_view = view(rv, weights_shape) |
| 25 | + centered = sub(x, rm_view) |
| 26 | + eps_full = full(eps_shape, eps) |
| 27 | + var_eps = add(rv_view, eps_full) |
| 28 | + inv_sqrt = rsqrt(var_eps) |
| 29 | + normed = mul(centered, inv_sqrt) |
| 30 | + weighted = mul(normed, w_view) |
| 31 | + biased = add(weighted, b_view) |
| 32 | +
|
| 33 | + Source: https://pytorch.org/docs/stable/generated/torch.nn.BatchNorm2d.html |
| 34 | + """ |
| 35 | + |
| 36 | + def call(self, graph_module: torch.fx.GraphModule) -> PassResult: # noqa: C901 |
| 37 | + bn_ops = ( |
| 38 | + exir_ops.edge.aten._native_batch_norm_legit.no_stats, |
| 39 | + exir_ops.edge.aten._native_batch_norm_legit_no_training.default, |
| 40 | + torch.ops.aten._native_batch_norm_legit_no_training.default, |
| 41 | + torch.ops.aten.batch_norm.default, |
| 42 | + torch.ops.aten.native_batch_norm.default, |
| 43 | + ) |
| 44 | + |
| 45 | + for node in graph_module.graph.nodes: |
| 46 | + if node.op != "call_function" or node.target not in bn_ops: |
| 47 | + continue |
| 48 | + |
| 49 | + if node.target in ( |
| 50 | + torch.ops.aten.batch_norm.default, |
| 51 | + torch.ops.aten.native_batch_norm.default, |
| 52 | + ): |
| 53 | + # signature: (input, weight, bias, mean, var, training, momentum, eps, cudnn_enabled) |
| 54 | + # pos‐arg 5 is training |
| 55 | + training = node.kwargs.get("training", False) |
| 56 | + if len(node.args) > 5: |
| 57 | + training = node.args[5] |
| 58 | + if training: |
| 59 | + # skip training‐mode batchnorm |
| 60 | + continue |
| 61 | + |
| 62 | + # Extract args |
| 63 | + args = node.args |
| 64 | + meta = node.meta |
| 65 | + |
| 66 | + # Default eps |
| 67 | + eps: float = torch.finfo().eps |
| 68 | + # weight and bias may be None |
| 69 | + x = args[0] |
| 70 | + weight = args[1] if len(args) > 1 else None |
| 71 | + bias = args[2] if len(args) > 2 else None |
| 72 | + running_mean = args[3] |
| 73 | + running_var = args[4] |
| 74 | + if len(args) > 6: |
| 75 | + eps = args[6] |
| 76 | + |
| 77 | + # Determine shapes |
| 78 | + val = meta.get("val") |
| 79 | + ref_tensor = val[0] if isinstance(val, tuple) else val |
| 80 | + shape = tuple(ref_tensor.size()) |
| 81 | + dtype = ref_tensor.dtype |
| 82 | + rank = len(shape) |
| 83 | + |
| 84 | + # channel dimension is 1 for BatchNorm2d |
| 85 | + channel_axis = 1 |
| 86 | + weights_shape = [1] * rank |
| 87 | + weights_shape[channel_axis] = shape[channel_axis] |
| 88 | + num_features = shape[channel_axis] |
| 89 | + |
| 90 | + # Ops to use |
| 91 | + sub_op = exir_ops.edge.aten.sub.Tensor |
| 92 | + view_op = exir_ops.edge.aten.view_copy.default |
| 93 | + full_op = exir_ops.edge.aten.full.default |
| 94 | + add_op = exir_ops.edge.aten.add.Tensor |
| 95 | + rsqrt_op = exir_ops.edge.aten.rsqrt.default |
| 96 | + mul_op = exir_ops.edge.aten.mul.Tensor |
| 97 | + |
| 98 | + # Begin decomposition |
| 99 | + with graph_module.graph.inserting_before(node): |
| 100 | + # reshape running stats |
| 101 | + rm_view = create_node( |
| 102 | + graph_module.graph, |
| 103 | + view_op, |
| 104 | + args=(running_mean, weights_shape), |
| 105 | + from_node=node, |
| 106 | + ) |
| 107 | + rv_view = create_node( |
| 108 | + graph_module.graph, |
| 109 | + view_op, |
| 110 | + args=(running_var, weights_shape), |
| 111 | + from_node=node, |
| 112 | + ) |
| 113 | + # center input |
| 114 | + centered = create_node( |
| 115 | + graph_module.graph, |
| 116 | + sub_op, |
| 117 | + args=(x, rm_view), |
| 118 | + from_node=node, |
| 119 | + ) |
| 120 | + # epsilon tensor |
| 121 | + eps_shape = [1] * rank |
| 122 | + eps_full = create_node( |
| 123 | + graph_module.graph, |
| 124 | + full_op, |
| 125 | + args=(eps_shape, eps), |
| 126 | + kwargs={"dtype": dtype}, |
| 127 | + from_node=node, |
| 128 | + ) |
| 129 | + # var + eps |
| 130 | + var_eps = create_node( |
| 131 | + graph_module.graph, |
| 132 | + add_op, |
| 133 | + args=(rv_view, eps_full), |
| 134 | + from_node=node, |
| 135 | + ) |
| 136 | + # inverse sqrt |
| 137 | + inv_sqrt = create_node( |
| 138 | + graph_module.graph, |
| 139 | + rsqrt_op, |
| 140 | + args=(var_eps,), |
| 141 | + from_node=node, |
| 142 | + ) |
| 143 | + # normalized |
| 144 | + normed = create_node( |
| 145 | + graph_module.graph, |
| 146 | + mul_op, |
| 147 | + args=(centered, inv_sqrt), |
| 148 | + from_node=node, |
| 149 | + ) |
| 150 | + |
| 151 | + # weight |
| 152 | + if weight is None: |
| 153 | + one = create_node( |
| 154 | + graph_module.graph, |
| 155 | + full_op, |
| 156 | + args=([num_features], 1), |
| 157 | + kwargs={"dtype": dtype}, |
| 158 | + from_node=node, |
| 159 | + ) |
| 160 | + w_view = create_node( |
| 161 | + graph_module.graph, |
| 162 | + view_op, |
| 163 | + args=(one, weights_shape), |
| 164 | + from_node=node, |
| 165 | + ) |
| 166 | + else: |
| 167 | + w_view = create_node( |
| 168 | + graph_module.graph, |
| 169 | + view_op, |
| 170 | + args=(weight, weights_shape), |
| 171 | + from_node=node, |
| 172 | + ) |
| 173 | + weighted = create_node( |
| 174 | + graph_module.graph, |
| 175 | + mul_op, |
| 176 | + args=(normed, w_view), |
| 177 | + from_node=node, |
| 178 | + ) |
| 179 | + |
| 180 | + # bias |
| 181 | + if bias is None: |
| 182 | + zero = create_node( |
| 183 | + graph_module.graph, |
| 184 | + full_op, |
| 185 | + args=([num_features], 0), |
| 186 | + kwargs={"dtype": dtype}, |
| 187 | + from_node=node, |
| 188 | + ) |
| 189 | + b_view = create_node( |
| 190 | + graph_module.graph, |
| 191 | + view_op, |
| 192 | + args=(zero, weights_shape), |
| 193 | + from_node=node, |
| 194 | + ) |
| 195 | + else: |
| 196 | + b_view = create_node( |
| 197 | + graph_module.graph, |
| 198 | + view_op, |
| 199 | + args=(bias, weights_shape), |
| 200 | + from_node=node, |
| 201 | + ) |
| 202 | + final_out = create_node( |
| 203 | + graph_module.graph, |
| 204 | + add_op, |
| 205 | + args=(weighted, b_view), |
| 206 | + from_node=node, |
| 207 | + ) |
| 208 | + |
| 209 | + users = [u for u in node.users if u is not node] |
| 210 | + node.replace_all_uses_with(final_out) |
| 211 | + for u in users: |
| 212 | + if u.target == operator.getitem: |
| 213 | + u.replace_all_uses_with(final_out) |
| 214 | + graph_module.graph.erase_node(node) |
| 215 | + graph_module.graph.eliminate_dead_code() |
| 216 | + |
| 217 | + graph_module.recompile() |
| 218 | + new_gm = super().call(graph_module).graph_module |
| 219 | + return PassResult(new_gm, True) |
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