Rewrite size/stride/numel TensorVariable handling (#103438)
The main concept behind this refactor is this: if we know that a size/stride/etc is constant, do NOT trace it into the graph, EXCEPT for any preexisting special cases that applied for static shapes. The refactor unfolds like this:
1. Delete the `dynamic_shapes` branches in torch/_dynamo/variables/builder.py which accept int/float/bool outputs. This is over-aggressive and we don't want to allow this (because if the operator returns a constant, we shouldn't have called wrap_fx_proxy in the first place.) This causes a bunch of failures because we are blindly feeding the result of size() call to wrap_fx_proxy when dynamic shapes is enabled.
2. Modify TensorVariable.call_method in torch/_dynamo/variables/tensor.py to avoid sending constant ints to wrap_fx_proxy. After normal specialization (which should be deleted, see https://github.com/pytorch/pytorch/pull/103434) we consult the fake tensor to see if the values in question have free variables or not. If they don't we short circuit tracing into graph. We only trace into graph if the operation in question is truly symbolic. Note that there is a near miss here: it's OK to trace x.size() call entirely into the graph, even if it doesn't have all dynamic shapes, because operator.getitem with int output is special cased in builder.py. This is a preexisting special case and I don't try to get rid of it.
3. It turns out that the change here also breaks torch_np compatibility layer. So I completely rewrite getattr handling in torch/_dynamo/variables/tensor.py to follow the same pattern (only trace into graph if truly dynamic).
There's some minor housekeeping in torch/fx/experimental/symbolic_shapes.py and some test files.
Signed-off-by: Edward Z. Yang <ezyang@meta.com>
Pull Request resolved: https://github.com/pytorch/pytorch/pull/103438
Approved by: https://github.com/larryliu0820
