Python Interface for Jiterator
This PR allows user to author a CUDA kernel in python.
```
from torch.cuda.jiterator import create_jit_fn
code_string = "template <typename T> T my_kernel(T x, T y, T alpha) { return -x * y + x - y + alpha; }"
jitted_fn = create_jit_fn(code_string, alpha=0)
a = torch.rand(3, device='cuda')
b = torch.rand(3, device='cuda')
result = jitted_fn(a, b, alpha=1.0)
```
Limitations:
- Only supports elementwise kernel
- 1~8 tensor inputs (empty input, e.g. factory methods, is not supported)
- inputs tensors must live in cuda device
- cpu Scalar is not supported
- kwargs must be pre-declared when calling create_jit_fn
- kwargs must be convertible to at::Scalar, one of float64, int64_t, bool. (complex not support for now)
TODOs:
- [x] consolidate union and c10::variant implementation
- [x] plug into existing op testing framework
- [ ] rename files, place files in the right folder
- [ ] place util functions in the right file
- [x] enforce assumptions in python interface e.g <8 inputs, kwargs types
- [x] Add user-facing documentation
Pull Request resolved: https://github.com/pytorch/pytorch/pull/76394
Approved by: https://github.com/mruberry
