Always create ShapeEnv, always apply unspec logic (#103302)
Originally, my goal for this PR was to remove the `dynamic_shapes` tests in torch/_dynamo/variables/builder.py. However, one thing lead to another, and it turns out that it was easiest to do all of the following in one go:
* Unconditionally allocate a ShapeEnv, no matter if dynamic_shapes is enabled or not (torch/_dynamo/output_graph.py). There is a small adjustment to export torch/_dynamo/eval_frame.py to account for the fact that a ShapeEnv always exists, even if you're not doing symbolic export.
* Remove dynamic_shapes test from unspec logic (torch/_dynamo/variables/builder.py), the original goal
* Specialize strides and storage offset if all sizes are dynamic (torch/fx/experimental/symbolic_shapes.py). This is required to deal with unconditional ShapeEnv: if a ShapeEnv exist, fake tensor-ification may choose to allocate symbols. The idea is that with `automatic_dynamic_shapes == False`, Dynamo should never request dynamic sizes, but this invariant was not upheld for nontrivial strides/offset.
The rest are just auxiliary fixups from the above:
* Workaround bug in FakeTensorProp where sometimes it doesn't return a FakeTensor (torch/fx/passes/fake_tensor_prop.py), see https://github.com/pytorch/pytorch/pull/103395 for follow up
* Make ShapeProp correctly handle int inputs (torch/fx/passes/shape_prop.py)
* Disable indexing strength reduction if `assume_static_by_default` is False (torch/_inductor/codegen/triton.py)
* Fix hf_T5_generate to NOT toggle `assume_static_by_default` if dynamic shapes is not enabled (benchmarks/dynamo/common.py); technically this is not necessary anymore but it's in for safety.
Signed-off-by: Edward Z. Yang <ezyang@meta.com>
Pull Request resolved: https://github.com/pytorch/pytorch/pull/103302
Approved by: https://github.com/voznesenskym
