Implements cpu_kernel_multiple_outputs and torch.frexp (#51097)
Summary:
Close https://github.com/pytorch/pytorch/issues/51108
Related https://github.com/pytorch/pytorch/issues/38349
This PR implements the `cpu_kernel_multiple_outputs` to support returning multiple values in a CPU kernel.
```c++
auto iter = at::TensorIteratorConfig()
.add_output(out1)
.add_output(out2)
.add_input(in1)
.add_input(in2)
.build();
at::native::cpu_kernel_multiple_outputs(iter,
[=](float a, float b) -> std::tuple<float, float> {
float add = a + b;
float mul = a * b;
return std::tuple<float, float>(add, mul);
}
);
```
The `out1` will equal to `torch.add(in1, in2)`, while the result of `out2` will be `torch.mul(in1, in2)`.
It helps developers implement new torch functions that return two tensors more conveniently, such as NumPy-like functions [divmod](https://numpy.org/doc/1.18/reference/generated/numpy.divmod.html?highlight=divmod#numpy.divmod) and [frexp](https://numpy.org/doc/stable/reference/generated/numpy.frexp.html#numpy.frexp).
This PR adds `torch.frexp` function to exercise the new functionality provided by `cpu_kernel_multiple_outputs`.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/51097
Reviewed By: albanD
Differential Revision: D26982619
Pulled By: heitorschueroff
fbshipit-source-id: cb61c7f2c79873ab72ab5a61cbdb9203531ad469
