Fix fake fusion for convolutions without bias (#3353)

Summary:

Fix `AttributeError` when performing fake fusion on convolution layers without bias by creating a zero-filled bias parameter instead of attempting to access requires_grad on None.

Reviewed By: jerryzh168

Differential Revision: D87356763

Author: balakv504

test/quantization/pt2e/test_quantize_pt2e.py

@@ -157,29 +157,23 @@ def test_chunked_bn_fusion(self):
         n_chunks = 3
         in_channels = 1
         out_channels = 32
-        m = ConvWithSharedWeightInExportedModel(n_chunks, in_channels, out_channels)
-        m.bn.running_var = torch.nn.Parameter(
-            torch.rand(out_channels) * 1e-2, requires_grad=False
-        )
+        for bias in [True, False]:
+            m = ConvWithSharedWeightInExportedModel(n_chunks, in_channels, out_channels, bias=bias)
+            m.bn.running_var = torch.nn.Parameter(
+                torch.rand(out_channels) * 1e-2, requires_grad=False
+            )
 
-        m.eval()
-        example_inputs = (torch.rand(batch_size, n_chunks, 32, 32),)
-        ref_outputs = m(*example_inputs)
-        traced_model = torch.export.export(m, example_inputs, strict=True).module()
-        traced_outputs = traced_model(*example_inputs)
-        prepared_model = prepare_pt2e(traced_model, XNNPACKQuantizer())
-        prepared_outputs = prepared_model(*example_inputs)
-
-        if isinstance(ref_outputs, (tuple, list)):
-            for ref, prepared, traced in zip(
-                ref_outputs, prepared_outputs, traced_outputs
-            ):
-                torch.testing.assert_close(ref, traced)
-                torch.testing.assert_close(traced, prepared)
-        else:
+            m.eval()
+            example_inputs = (torch.rand(batch_size, n_chunks, 32, 32),)
+            ref_outputs = m(*example_inputs)
+            traced_model = torch.export.export(m, example_inputs, strict=True).module()
+            traced_outputs = traced_model(*example_inputs)
+            prepared_model = prepare_pt2e(traced_model, XNNPACKQuantizer())
+            prepared_outputs = prepared_model(*example_inputs)
             torch.testing.assert_close(ref_outputs, traced_outputs)
             torch.testing.assert_close(traced_outputs, prepared_outputs)
 
+
     def test_wo_annotate_conv_output_quantizer(self):
         # TODO: use OP_TO_ANNOTATOR
         class BackendAQuantizer(Quantizer):

torchao/quantization/pt2e/utils.py

@@ -710,10 +710,11 @@ def fold_bn_weights_into_conv_node(
         conv_args.append(None)
 
     if fake_fuse:
-        fused_weight, fused_bias = (
-            torch.nn.Parameter(conv_w, conv_w.requires_grad),
-            torch.nn.Parameter(conv_b, conv_b.requires_grad),
-        )
+        fused_weight = torch.nn.Parameter(conv_w, conv_w.requires_grad)
+        if conv_b is not None:
+            fused_bias = torch.nn.Parameter(conv_b, conv_b.requires_grad)
+        else:
+            fused_bias = torch.nn.Parameter(torch.zeros_like(bn_rm), requires_grad=conv_w.requires_grad)
     else:
         fused_weight, fused_bias = fuse_conv_bn_weights(
             conv_w, conv_b, bn_rm, bn_rv, bn_eps, bn_w, bn_b, transpose=transpose

torchao/testing/model_architectures.py

@@ -82,11 +82,11 @@ def forward(self, x):
 
 class ConvWithSharedWeightInExportedModel(nn.Module):
     def __init__(
-        self, n_chunks, in_channels, out_channels, kernel_size=3, stride=1, padding=1
+        self, n_chunks, in_channels, out_channels, kernel_size=3, stride=1, padding=1, bias=True
     ) -> None:
         super().__init__()
         self.n_chunks = n_chunks
-        self.conv = nn.Conv2d(in_channels, out_channels, kernel_size, stride, padding)
+        self.conv = nn.Conv2d(in_channels, out_channels, kernel_size, stride, padding, bias=bias)
         self.bn = nn.BatchNorm2d(out_channels)
         self.relu = nn.ReLU(inplace=True)