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Find and fix an export issue due to dynamic shapes¶
LLMs must be exported with dynamic shapes and it is common that
a static dimension turns into a static ones. The error message from
pytorch tells the user to define TORCH_LOGS="+dynamic"
but it shows a very long list of messages where we need
to find the string range_refined_to_singleton and that
does not really indicates where it comes from. The example
shows how to tweak pytorch to get that information until
it gets better.
A model with an export issue¶
The following model implies the first dimension of x is equal to 1
or equal to the number of element in the list ys.
It is not really dynamic. It looks obvious here but
it is difficult to find deep inside a big model.
import traceback
import torch
from onnx_diagnostic import doc
from onnx_diagnostic.torch_export_patches import torch_export_patches
class ModelWithIssue(torch.nn.Module):
def forward(self, x: torch.Tensor, ys: list[torch.Tensor]):
caty = torch.cat([y.unsqueeze(0) for y in ys], axis=0)
z = x * caty
return z
inputs = (torch.rand(2, 3, 1), [torch.rand(3, 4), torch.rand(3, 4)])
model = ModelWithIssue()
model(*inputs)
tensor([[[0.3113, 0.5510, 0.4920, 0.3743],
[0.2655, 0.0550, 0.0221, 0.1182],
[0.3164, 0.2754, 0.1045, 0.1932]],
[[0.2115, 0.5465, 0.0468, 0.5540],
[0.2177, 0.1544, 0.1444, 0.2867],
[0.4253, 0.2722, 0.4732, 0.5565]]])
Let’s export.
DYN = torch.export.Dim.DYNAMIC
dyn_shapes = ({0: DYN, 1: DYN}, [{0: DYN, 1: DYN}, {0: DYN, 1: DYN}])
try:
ep = torch.export.export(model, inputs, dynamic_shapes=dyn_shapes)
print(ep)
except Exception as e:
print("-- ERROR:")
print(e)
-- ERROR:
Constraints violated (L['x'].size()[0])! For more information, run with TORCH_LOGS="+dynamic".
- You marked L['x'].size()[0] as dynamic but your code specialized it to be a constant (2). If you're using mark_dynamic, either remove it or use maybe_mark_dynamic. If you're using Dim.DYNAMIC, replace it with either Dim.STATIC or Dim.AUTO.
The error above occurred when calling torch.export.export. If you would like to view some more information about this error, and get a list of all other errors that may occur in your export call, you can replace your `export()` call with `draft_export()`.
The error shows:
Constraints violated (L['args'][0][0].size()[0])!
For more information, run with TORCH_LOGS="+dynamic".
- Not all values of RelaxedUnspecConstraint(L['args'][0][0].size()[0])
are valid because L['args'][0][0].size()[0] was inferred to be a constant (2).
Where does it happens? That’s a tricky question we need to answer. The message is raised from torch.fx.experimental.symbolic_shapes.ShapeEnv._set_replacement. One way to find the exact location is to retrieve a stack trace by inserting an assert such as the following:
assert msg != "range_refined_to_singleton", (
f"A dynamic dimension becomes static! "
f"a={a!r}, tgt={tgt!r}, msg={msg!r}, tgt_bound={tgt_bound}"
)
Stop when a dynamic dimension turns static¶
We use torch_export_patches
to replace torch implementation by a new one raising the exception
mentioned in previous section.
with torch_export_patches(stop_if_static=1, verbose=1):
try:
torch.export.export(model, inputs, dynamic_shapes=dyn_shapes)
except (AssertionError, torch._dynamo.exc.TorchRuntimeError) as e:
print("-- It failed as excepted.")
print(f"-- final error is {e}")
print("-- Stack Trace")
print(traceback.format_exc())
# The stack trace is quite long but the first line referring to this example
# is the following one. It points out the line turing a dynamic dimension into
# static.
#
# .. code-block::
#
# File "onnx-diagnostic/_doc/examples/plot_export_locate_issue.py", line 25, in forward
# z = x * caty
[torch_export_patches] replace torch.jit.isinstance, torch._dynamo.mark_static_address
[torch_export_patches] sympy.__version__='1.13.3'
[torch_export_patches] patch sympy
[torch_export_patches] torch.__version__='2.9.0.dev20250723+cu126'
[torch_export_patches] stop_if_static=1
[torch_export_patches] patch pytorch
[torch_export_patches] modifies shape constraints
[torch_export_patches] assert when a dynamic dimension turns static
[torch_export_patches] replaces ShapeEnv._set_replacement
[torch_export_patches] replaces ShapeEnv._log_guard
[torch_export_patches] done patching
-- It failed as excepted.
-- final error is patched_ShapeEnv: A dynamic dimension becomes static! a=s77, tgt=2, msg='range_refined_to_singleton', tgt_bound=VR[2, 2]
-- Stack Trace
Traceback (most recent call last):
File "~/github/onnx-diagnostic/_doc/examples/plot_export_locate_issue.py", line 90, in <module>
torch.export.export(model, inputs, dynamic_shapes=dyn_shapes)
File "~/vv/this312/lib/python3.12/site-packages/torch/export/__init__.py", line 304, in export
raise e
File "~/vv/this312/lib/python3.12/site-packages/torch/export/__init__.py", line 271, in export
return _export(
^^^^^^^^
File "~/vv/this312/lib/python3.12/site-packages/torch/export/_trace.py", line 1150, in wrapper
raise e
File "~/vv/this312/lib/python3.12/site-packages/torch/export/_trace.py", line 1116, in wrapper
ep = fn(*args, **kwargs)
^^^^^^^^^^^^^^^^^^^
File "~/vv/this312/lib/python3.12/site-packages/torch/export/exported_program.py", line 124, in wrapper
return fn(*args, **kwargs)
^^^^^^^^^^^^^^^^^^^
File "~/vv/this312/lib/python3.12/site-packages/torch/export/_trace.py", line 2163, in _export
ep = _export_for_training(
^^^^^^^^^^^^^^^^^^^^^
File "~/vv/this312/lib/python3.12/site-packages/torch/export/_trace.py", line 1150, in wrapper
raise e
File "~/vv/this312/lib/python3.12/site-packages/torch/export/_trace.py", line 1116, in wrapper
ep = fn(*args, **kwargs)
^^^^^^^^^^^^^^^^^^^
File "~/vv/this312/lib/python3.12/site-packages/torch/export/exported_program.py", line 124, in wrapper
return fn(*args, **kwargs)
^^^^^^^^^^^^^^^^^^^
File "~/vv/this312/lib/python3.12/site-packages/torch/export/_trace.py", line 2026, in _export_for_training
export_artifact = export_func(
^^^^^^^^^^^^
File "~/vv/this312/lib/python3.12/site-packages/torch/export/_trace.py", line 1968, in _non_strict_export
aten_export_artifact = _to_aten_func( # type: ignore[operator]
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
File "~/vv/this312/lib/python3.12/site-packages/torch/export/_trace.py", line 1762, in _export_to_aten_ir_make_fx
gm, graph_signature = transform(_make_fx_helper)(
^^^^^^^^^^^^^^^^^^^^^^^^^^^
File "~/vv/this312/lib/python3.12/site-packages/torch/export/_trace.py", line 1891, in _aot_export_non_strict
gm, sig = aot_export(wrapped_mod, args, kwargs=kwargs, **flags)
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
File "~/vv/this312/lib/python3.12/site-packages/torch/export/_trace.py", line 1676, in _make_fx_helper
gm = make_fx(
^^^^^^^^
File "~/vv/this312/lib/python3.12/site-packages/torch/fx/experimental/proxy_tensor.py", line 2351, in wrapped
return make_fx_tracer.trace(f, *args)
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
File "~/vv/this312/lib/python3.12/site-packages/torch/fx/experimental/proxy_tensor.py", line 2283, in trace
return self._trace_inner(f, *args)
^^^^^^^^^^^^^^^^^^^^^^^^^^^
File "~/vv/this312/lib/python3.12/site-packages/torch/fx/experimental/proxy_tensor.py", line 2254, in _trace_inner
t = dispatch_trace(
^^^^^^^^^^^^^^^
File "~/vv/this312/lib/python3.12/site-packages/torch/_compile.py", line 53, in inner
return disable_fn(*args, **kwargs)
^^^^^^^^^^^^^^^^^^^^^^^^^^^
File "~/vv/this312/lib/python3.12/site-packages/torch/_dynamo/eval_frame.py", line 1004, in _fn
return fn(*args, **kwargs)
^^^^^^^^^^^^^^^^^^^
File "~/vv/this312/lib/python3.12/site-packages/torch/fx/experimental/proxy_tensor.py", line 1283, in dispatch_trace
graph = tracer.trace(root, concrete_args) # type: ignore[arg-type]
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
File "~/vv/this312/lib/python3.12/site-packages/torch/fx/experimental/proxy_tensor.py", line 1865, in trace
res = super().trace(root, concrete_args)
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
File "~/vv/this312/lib/python3.12/site-packages/torch/_dynamo/eval_frame.py", line 1004, in _fn
return fn(*args, **kwargs)
^^^^^^^^^^^^^^^^^^^
File "~/vv/this312/lib/python3.12/site-packages/torch/fx/_symbolic_trace.py", line 850, in trace
(self.create_arg(fn(*args)),),
^^^^^^^^^
File "~/vv/this312/lib/python3.12/site-packages/torch/fx/experimental/proxy_tensor.py", line 1341, in wrapped
out = f(*tensors) # type:ignore[call-arg]
^^^^^^^^^^^
File "<string>", line 1, in <lambda>
File "~/vv/this312/lib/python3.12/site-packages/torch/export/_trace.py", line 1580, in wrapped_fn
return tuple(flat_fn(*args))
^^^^^^^^^^^^^^
File "~/vv/this312/lib/python3.12/site-packages/torch/_functorch/_aot_autograd/utils.py", line 184, in flat_fn
tree_out = fn(*args, **kwargs)
^^^^^^^^^^^^^^^^^^^
File "~/vv/this312/lib/python3.12/site-packages/torch/_functorch/_aot_autograd/graph_capture_wrappers.py", line 1138, in functional_call
out = mod(*args[params_len:], **kwargs)
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
File "~/vv/this312/lib/python3.12/site-packages/torch/fx/_symbolic_trace.py", line 825, in module_call_wrapper
return self.call_module(mod, forward, args, kwargs)
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
File "~/vv/this312/lib/python3.12/site-packages/torch/fx/experimental/proxy_tensor.py", line 1935, in call_module
return Tracer.call_module(self, m, forward, args, kwargs)
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
File "~/vv/this312/lib/python3.12/site-packages/torch/fx/_symbolic_trace.py", line 542, in call_module
ret_val = forward(*args, **kwargs)
^^^^^^^^^^^^^^^^^^^^^^^^
File "~/vv/this312/lib/python3.12/site-packages/torch/fx/_symbolic_trace.py", line 818, in forward
return _orig_module_call(mod, *args, **kwargs)
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
File "~/vv/this312/lib/python3.12/site-packages/torch/nn/modules/module.py", line 1773, in _wrapped_call_impl
return self._call_impl(*args, **kwargs)
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
File "~/vv/this312/lib/python3.12/site-packages/torch/nn/modules/module.py", line 1784, in _call_impl
return forward_call(*args, **kwargs)
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
File "~/vv/this312/lib/python3.12/site-packages/torch/export/_trace.py", line 1875, in forward
tree_out = mod(*args, **kwargs)
^^^^^^^^^^^^^^^^^^^^
File "~/vv/this312/lib/python3.12/site-packages/torch/fx/_symbolic_trace.py", line 825, in module_call_wrapper
return self.call_module(mod, forward, args, kwargs)
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
File "~/vv/this312/lib/python3.12/site-packages/torch/fx/experimental/proxy_tensor.py", line 1935, in call_module
return Tracer.call_module(self, m, forward, args, kwargs)
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
File "~/vv/this312/lib/python3.12/site-packages/torch/fx/_symbolic_trace.py", line 542, in call_module
ret_val = forward(*args, **kwargs)
^^^^^^^^^^^^^^^^^^^^^^^^
File "~/vv/this312/lib/python3.12/site-packages/torch/fx/_symbolic_trace.py", line 818, in forward
return _orig_module_call(mod, *args, **kwargs)
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
File "~/vv/this312/lib/python3.12/site-packages/torch/nn/modules/module.py", line 1773, in _wrapped_call_impl
return self._call_impl(*args, **kwargs)
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
File "~/vv/this312/lib/python3.12/site-packages/torch/nn/modules/module.py", line 1784, in _call_impl
return forward_call(*args, **kwargs)
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
File "~/github/onnx-diagnostic/_doc/examples/plot_export_locate_issue.py", line 35, in forward
z = x * caty
~~^~~~~~
File "~/vv/this312/lib/python3.12/site-packages/torch/fx/experimental/proxy_tensor.py", line 1389, in __torch_function__
return func(*args, **kwargs)
^^^^^^^^^^^^^^^^^^^^^
File "~/vv/this312/lib/python3.12/site-packages/torch/fx/experimental/proxy_tensor.py", line 1436, in __torch_function__
return func(*args, **kwargs)
^^^^^^^^^^^^^^^^^^^^^
File "~/vv/this312/lib/python3.12/site-packages/torch/_export/non_strict_utils.py", line 1066, in __torch_function__
return func(*args, **kwargs)
^^^^^^^^^^^^^^^^^^^^^
File "~/vv/this312/lib/python3.12/site-packages/torch/_ops.py", line 961, in handler
return torch._library.utils.handle_dispatch_mode(
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
File "~/vv/this312/lib/python3.12/site-packages/torch/_library/utils.py", line 296, in handle_dispatch_mode
return curr_mode.__torch_dispatch__(op_overload, overload_types, args, kwargs)
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
File "~/vv/this312/lib/python3.12/site-packages/torch/utils/_stats.py", line 28, in wrapper
return fn(*args, **kwargs)
^^^^^^^^^^^^^^^^^^^
File "~/vv/this312/lib/python3.12/site-packages/torch/fx/experimental/proxy_tensor.py", line 1491, in __torch_dispatch__
return proxy_call(self, func, self.pre_dispatch, args, kwargs)
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
File "~/vv/this312/lib/python3.12/site-packages/torch/fx/experimental/proxy_tensor.py", line 974, in proxy_call
out = func(*args, **kwargs)
^^^^^^^^^^^^^^^^^^^^^
File "~/vv/this312/lib/python3.12/site-packages/torch/_ops.py", line 840, in __call__
return self._op(*args, **kwargs)
^^^^^^^^^^^^^^^^^^^^^^^^^
File "~/vv/this312/lib/python3.12/site-packages/torch/utils/_stats.py", line 28, in wrapper
return fn(*args, **kwargs)
^^^^^^^^^^^^^^^^^^^
File "~/vv/this312/lib/python3.12/site-packages/torch/_subclasses/fake_tensor.py", line 1352, in __torch_dispatch__
return self.dispatch(func, types, args, kwargs)
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
File "~/vv/this312/lib/python3.12/site-packages/torch/_subclasses/fake_tensor.py", line 2068, in dispatch
return self._cached_dispatch_impl(func, types, args, kwargs)
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
File "~/vv/this312/lib/python3.12/site-packages/torch/_subclasses/fake_tensor.py", line 1487, in _cached_dispatch_impl
output = self._dispatch_impl(func, types, args, kwargs)
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
File "~/vv/this312/lib/python3.12/site-packages/torch/_subclasses/fake_tensor.py", line 2587, in _dispatch_impl
return maybe_propagate_real_tensors(fast_impl(self, *args, **kwargs))
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
File "~/vv/this312/lib/python3.12/site-packages/torch/_subclasses/fake_impls.py", line 962, in fast_binary_impl
final_shape = infer_size(final_shape, shape)
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
File "~/github/onnx-diagnostic/onnx_diagnostic/torch_export_patches/patches/patch_torch.py", line 119, in patched_infer_size
b3 = guard_size_oblivious(sizeA == sizeB)
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
File "~/vv/this312/lib/python3.12/site-packages/torch/fx/experimental/symbolic_shapes.py", line 476, in guard_size_oblivious
return expr.node.guard_size_oblivious("", 0)
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
File "~/vv/this312/lib/python3.12/site-packages/torch/fx/experimental/sym_node.py", line 596, in guard_size_oblivious
r = self.evaluate(size_oblivious=True)
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
File "~/vv/this312/lib/python3.12/site-packages/torch/fx/experimental/sym_node.py", line 512, in evaluate
return self.shape_env.evaluate_sym_node(self, size_oblivious)
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
File "~/vv/this312/lib/python3.12/site-packages/torch/fx/experimental/symbolic_shapes.py", line 7237, in evaluate_sym_node
return self.evaluate_expr(
^^^^^^^^^^^^^^^^^^^
File "~/vv/this312/lib/python3.12/site-packages/torch/fx/experimental/symbolic_shapes.py", line 7337, in evaluate_expr
return self._inner_evaluate_expr(
^^^^^^^^^^^^^^^^^^^^^^^^^^
File "~/vv/this312/lib/python3.12/site-packages/torch/fx/experimental/recording.py", line 272, in wrapper
return retlog(fn(*args, **kwargs))
^^^^^^^^^^^^^^^^^^^
File "~/vv/this312/lib/python3.12/site-packages/torch/fx/experimental/symbolic_shapes.py", line 7360, in _inner_evaluate_expr
return self._evaluate_expr(
^^^^^^^^^^^^^^^^^^^^
File "~/vv/this312/lib/python3.12/site-packages/torch/fx/experimental/symbolic_shapes.py", line 7629, in _evaluate_expr
self._maybe_guard_rel(g)
File "~/vv/this312/lib/python3.12/site-packages/torch/fx/experimental/symbolic_shapes.py", line 6882, in _maybe_guard_rel
self._refine_ranges(expr)
File "~/vv/this312/lib/python3.12/site-packages/torch/fx/experimental/symbolic_shapes.py", line 7833, in _refine_ranges
self._set_replacement(
File "~/github/onnx-diagnostic/onnx_diagnostic/torch_export_patches/patches/patch_torch.py", line 343, in _set_replacement
assert msg != "range_refined_to_singleton", (
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
AssertionError: patched_ShapeEnv: A dynamic dimension becomes static! a=s77, tgt=2, msg='range_refined_to_singleton', tgt_bound=VR[2, 2]
[torch_export_patches] remove patches
[torch_export_patches] restored sympy functions
[torch_export_patches] restored pytorch functions
[torch_export_patches] restored ShapeEnv._set_replacement
[torch_export_patches] restored ShapeEnv._log_guard
[torch_export_patches] restored shape constraints
doc.plot_legend(
"dynamic dimension\nwas inferred\nto be a constant", "torch.export.export", "tomato"
)
Total running time of the script: (0 minutes 0.635 seconds)
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