pytorch

a348975e - Add opteinsum backend to give users control (#86219)

Add opteinsum backend to give users control (#86219) This achieves the same things as https://github.com/pytorch/pytorch/pull/85908 but using backends instead of kwargs (which breaks torchscript unfortunately). This also does mean we let go of numpy compatibility BUT the wins here are that users can control what opt einsum they wanna do! The backend allows for..well you should just read the docs: ``` .. attribute:: torch.backends.opteinsum.enabled A :class:`bool` that controls whether opt_einsum is enabled (on by default). If so, torch.einsum will use opt_einsum (https://optimized-einsum.readthedocs.io/en/stable/path_finding.html) to calculate an optimal path of contraction for faster performance. .. attribute:: torch.backends.opteinsum.strategy A :class:`str` that specifies which strategies to try when `torch.backends.opteinsum.enabled` is True. By default, torch.einsum will try the "auto" strategy, but the "greedy" and "optimal" strategies are also supported. Note that the "optimal" strategy is factorial on the number of inputs as it tries all possible paths. See more details in opt_einsum's docs (https://optimized-einsum.readthedocs.io/en/stable/path_finding.html). ``` In trying (and failing) to land 85908, I discovered that jit script does NOT actually pull from python's version of einsum (because it cannot support variadic args nor kwargs). Thus I learned that jitted einsum does not subscribe to the new opt_einsum path calculation. Overall, this is fine since jit script is getting deprecated, but where is the best place to document this? ## Test plan: - added tests to CI - locally tested that trying to set the strategy to something invalid will error properly - locally tested that tests will pass even if you don't have opt-einsum - locally tested that setting the strategy when opt-einsum is not there will also error properly Pull Request resolved: https://github.com/pytorch/pytorch/pull/86219 Approved by: https://github.com/soulitzer, https://github.com/malfet