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Avoid stream sync in softmax #10499

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34e0a21
Use output_size argument in torch.repeat_interleave when index is pro…
spinjo Oct 13, 2025
bb9e9be
Extend test
spinjo Oct 13, 2025
88d9039
[pre-commit.ci] auto fixes from pre-commit.com hooks
pre-commit-ci[bot] Oct 13, 2025
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2 changes: 2 additions & 0 deletions test/utils/test_softmax.py
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Original file line number Diff line number Diff line change
Expand Up @@ -17,11 +17,13 @@ def test_softmax():
out = softmax(src, index)
assert out.tolist() == [0.5, 0.5, 1, 1]
assert softmax(src, ptr=ptr).tolist() == out.tolist()
assert softmax(src, index=index, ptr=ptr).tolist() == out.tolist()

src = src.view(-1, 1)
out = softmax(src, index)
assert out.tolist() == [[0.5], [0.5], [1], [1]]
assert softmax(src, ptr=ptr).tolist() == out.tolist()
assert softmax(src, index=index, ptr=ptr).tolist() == out.tolist()

jit = torch.jit.script(softmax)
assert torch.allclose(jit(src, index), out)
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7 changes: 5 additions & 2 deletions torch_geometric/utils/_softmax.py
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Original file line number Diff line number Diff line change
Expand Up @@ -65,11 +65,14 @@ def softmax(
size = ([1] * dim) + [-1]
count = ptr[1:] - ptr[:-1]
ptr = ptr.view(size)
output_size = index.shape[dim] if index is not None else None
src_max = segment(src.detach(), ptr, reduce='max')
src_max = src_max.repeat_interleave(count, dim=dim)
src_max = src_max.repeat_interleave(count, dim=dim,
output_size=output_size)
out = (src - src_max).exp()
out_sum = segment(out, ptr, reduce='sum') + 1e-16
out_sum = out_sum.repeat_interleave(count, dim=dim)
out_sum = out_sum.repeat_interleave(count, dim=dim,
output_size=output_size)
elif index is not None:
N = maybe_num_nodes(index, num_nodes)
src_max = scatter(src.detach(), index, dim, dim_size=N, reduce='max')
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