At high current implementation of constrains functions (constrain_as_**) will raise exception for the following code snippets:
```
def f(x):
a = x.item()
constrain_as_size(a, 4, 7)
return torch.empty((a, 4))
inp = torch.tensor([5])
ep = torch._export.export(f, (inp,))
```
The reason is because current constrain logic is:
1) Purely python so it won't survive AOT export (the full node is gone after AOT export since AOT export only maintains aten level op).
2) Utilize side effect to add range constraints for traced symbol's shape env ([code](9591e52880/torch/fx/experimental/symbolic_shapes.py (L370-L372))).
3) If runtime assertion is turned on (by default). [`_AddRuntimeAssertionsForConstraintsPass`](9591e52880/torch/_export/passes/add_runtime_assertions_for_constraints_pass.py (L98-L100)) will try to append assertion node based on range constrains extracted from shape env of symbol during another interpretation round.
4). However, since 1), in the round of AOT export, range constraints logic won't run for symbols generated during this round. And later there is no range constrains information available for assertion round and caused issue.
5) As a result of above, it will failure at `torch.empty((a, 4))` (there is no constrains for `a` that it must be positive).
The fix here is just to implement range constrain logic as a native aten op (CPU implementation as no-op) to make it be able to survive AOT export.
**NOTE:**
[Logic](2d745b95d7/torch/fx/experimental/symbolic_shapes.py (L350-L365C15)) within [`constrain_range`](2d745b95d7/torch/fx/experimental/symbolic_shapes.py (LL313C74-L313C74)) is split out as `constrain_range_int` to capture case when non `SymInt` is passed in and reused in the new `_constrain_range`. The reason is when non `SymInt` is provided:
* If it directly calls `sym_constrain_range`, the C++ version will be called which will be no-op.
* So in this case it calls `constrain_range_int` instead to be able to capture issue like user provides a input whose tensor's shape could be out of range during exporting, like the following for above code example:
```
...
inp = torch.tensor([10])
ep = torch._export.export(f, (inp,)) # immediately raise error
```
Differential Revision: [D46734204](https://our.internmc.facebook.com/intern/diff/D46734204)
Pull Request resolved: https://github.com/pytorch/pytorch/pull/103346
Approved by: https://github.com/tugsbayasgalan
Wrapper for users to insert constraints into model code.
The constraints will not be maintained in the graph after tracing through make_fx so retracing with dynamo/make_fx will not work. This will be supported after torch._assert supported is implemented. Then we can convert the constrain_range calls to torch._asserts.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/98433
Approved by: https://github.com/avikchaudhuri, https://github.com/tugsbayasgalan
Wrapper for users to insert constraints into model code.
The constraints will not be maintained in the graph after tracing through make_fx so retracing with dynamo/make_fx will not work. This will be supported after torch._assert supported is implemented. Then we can convert the constrain_range calls to torch._asserts.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/98433
Approved by: https://github.com/avikchaudhuri, https://github.com/tugsbayasgalan
