[c10/cuda] Reorganize device_count() and robustly surface ASAN warnings (#42249)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/42249
Main change is to bring Caffe2's superior error messages for cuda initialization into c10 and use them in all code paths.
Basic logic:
| Case | Call to device_count() | init_cuda, e.g. allocating tensor |
| -- | -- | -- |
| all good | non-zero | just works |
| no gpus | 0, no warning | throw exception with good message |
| driver issues | 0, produce warning | throw exception with good message |
| out of memory with ASAN | 0, produce warning| throw exception with ASAN message |
Previously, the error thrown from init_cuda was very generic and the ASAN warning (if any) was buried in the logs.
Other clean up changes:
* cache device_count() always in a static variable
* move all asan macros in c10
Test Plan:
Hard to unittest because of build modes. Verified manually that the behavior from the table above holds by running the following script in different modes (ASAN/no-ASAN, CUDA_VISIBLE_DEVICES=):
```
print('before import')
import torch
print('after import')
print('devices: ', torch.cuda.device_count())
x = torch.tensor([1,2,3])
print('tensor creation')
x = x.cuda()
print('moved to cuda')
```
Reviewed By: ngimel
Differential Revision: D22824329
fbshipit-source-id: 5314007313a3897fc955b02f8b21b661ae35fdf5
