Migrate `cos` and `cos_` from TH to ATen (CUDA) (#36653)
Summary:
Benchmark with same build settings on same system.
Closes https://github.com/pytorch/pytorch/issues/24545
gcc : version 7.5.0 (Ubuntu 7.5.0-3ubuntu1~18.04)
CUDA : 10.1
GPU : 1050ti
```python
import timeit
for n, t in [(10_000, 20000),
(100_000, 20000)]:
for dtype in ('torch.half', 'torch.float', 'torch.double'):
print(f'torch.cos(a) a.numel() == {n} for {t} times {dtype}')
print(timeit.timeit(f'torch.cos(a); torch.cuda.synchronize()',
setup=f'import torch; a=torch.arange({n}, dtype={dtype}, device="cuda")',
number=t))
```
Before:
```
torch.cos(a) a.numel() == 10000 for 20000 times torch.half
0.2797315450006863
torch.cos(a) a.numel() == 10000 for 20000 times torch.float
0.283109110998339
torch.cos(a) a.numel() == 10000 for 20000 times torch.double
0.3648525129974587
torch.cos(a) a.numel() == 100000 for 20000 times torch.half
0.34239949499897193
torch.cos(a) a.numel() == 100000 for 20000 times torch.float
0.33680364199972246
torch.cos(a) a.numel() == 100000 for 20000 times torch.double
1.0512770260102116
```
After:
```
torch.cos(a) a.numel() == 10000 for 20000 times torch.half
0.285825898999974
torch.cos(a) a.numel() == 10000 for 20000 times torch.float
0.2781305120001889
torch.cos(a) a.numel() == 10000 for 20000 times torch.double
0.34188826099989456
torch.cos(a) a.numel() == 100000 for 20000 times torch.half
0.29040409300023384
torch.cos(a) a.numel() == 100000 for 20000 times torch.float
0.28678944200009937
torch.cos(a) a.numel() == 100000 for 20000 times torch.double
1.065477349000048
```
Pull Request resolved: https://github.com/pytorch/pytorch/pull/36653
Differential Revision: D21164675
Pulled By: VitalyFedyunin
fbshipit-source-id: 5dd5d3af47c2a5527e1f4ab7669c2ed9a2293cee
