[SR] Eliminate extra permute ops before `aten::sum` (#74481)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/74481
This diff fixes an interesting performance issue related to `permute_copy`.
We see this pattern frequently:
```
y = torch.permute(x, (0, 2, 1))
z = torch.sum(y, dim=-1)
```
With copy variants off, we get a strided output from `permute`, and we hit this (faster) kernel in `sum`: https://github.com/pytorch/pytorch/blob/master/aten/src/ATen/native/cpu/SumKernel.cpp#L589
But with copy variants on, we get a contiguous output from `permute_copy`, which causes us to hit the slower reduction:
https://github.com/pytorch/pytorch/blob/master/aten/src/ATen/native/cpu/SumKernel.cpp#L597
But the permute is actually unnecessary, we can just statically turn the graph into this to ensure that the fast kernel is hit with copy variants on:
```
z = torch.sum(x, dim=1)
```
ghstack-source-id: 152003888
Reviewed By: navahgar
Differential Revision: D34992319
fbshipit-source-id: 0baf493708ee2180c899814a954d220d88ba1d4f
(cherry picked from commit 797b6beb26325c56012e406e14fe211c0b5d744d)
