Add at::symint:: namespace for ease of templated functions (#86329)
Our prevailing strategy for symbolic shapes in C++ is to only
write the SymInt version of the code, and pay a slight performance
tax from not knowing if it is symbolic or not. However, there are
some fastpath functions where this tax is unacceptable, and we want
to specialize for the int case. Sometimes, it is easy to template
the function; but when the function involves Tensors, it is not,
because the functions you may want to call are not templated,
e.g., t.view vs t.view_symint
This PR adds an at::symint:: namespace which contains templated
functions for all functions in PyTorch which you can use in this
way. To show this works, I refactored sum_to to stop incorrectly
reinterpret casting and instead use a template. Instead of
t.sizes(), we call at::symint::sizes<T>(t), and so forth.
The template functions are SFINAE'd using a template argument that
is not otherwise used. As such, deduction is impossible. Typically, deduction
is hard anyway, because many of the constructors are ambiguous (this
is why we split foo and foo_symint in the first place). So you must pass
a template argument to these functions.
These functions are codegened into Functions.h so they are subject
to per-operator headers. This matters most for methods, which likely
didn't include the per-operator header, so you will have to add an
include in that case. We never generate method variants for these.
Signed-off-by: Edward Z. Yang <ezyang@fb.com>
Pull Request resolved: https://github.com/pytorch/pytorch/pull/86329
Approved by: https://github.com/bdhirsh, https://github.com/voznesenskym
