[nvFuser] Working towards reductions, codegen improvements (#40864)
Summary:
Have basic reduction fusion working, and have improved code generator to approach performance of eager mode reductions. Coming soon will be pointwise-reduction fusions in a way that should prevent the possibility of hitting regressions. Also working on performant softmax kernels in the code generator which may be our next fusion target.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/40864
Reviewed By: ngimel
Differential Revision: D22392877
Pulled By: soumith
fbshipit-source-id: 457448a807d628b1035f6d90bc0abe8a87bf8447
