various TensorIterator speed improvements (#58810)
Summary:
1) remove pushing back to strides vector for 1D tensors, those strides are never used in the loop anyway
2) avoid calling get_data_ptrs unless necessary
3) don't call into assert_no_partial_overlap if tensorImpls are the same (assert_no_partial_overlap has this comparison too, but after a couple of nested function calls)
4) is_non_overlapping_and_dense instead of is_contiguous in memory overlap (which, for some reason, is faster than is_contiguous, though I hoped after is_contiguous is non-virtualized, it should be the same).
Altogether, brings instruction count down from ~110K to 102735 for the following binary inplace benchmark:
```
In [2]: timer = Timer("m1.add_(b);", setup="at::Tensor m1=torch::empty({1}); at::Tensor b = torch::empty({1});", language="c++", timer=timeit.default_timer)
...: stats=timer.collect_callgrind(number=30, repeats=3)
...: print(stats[1].as_standardized().stats(inclusive=False))
```
similar improvements for unary inplace.
Upd: returned stride packing for now, counts is now 104295, so packing is worth ~ 52 instructions, we should think about how to remove it safely.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/58810
Reviewed By: bhosmer
Differential Revision: D28664514
Pulled By: ngimel
fbshipit-source-id: 2e03cf90b37a411d9994a7607402645f1d8f3c93
Author
Natalia Gimelshein
