Summary:
This PR removes couple of macros throughout TH* as part of the re-factoring effort for ATen. Removing these macros should avoid confusion among developers who are trying to move things from TH* to ATen. This PR is part of the THCNumerics deprecation that I have been working on following up on mruberry's #9318. I am separating these two commits to see if removal of these macros doesn't upset the pytorch public CI, as well as internal builds.

- Commit 1248de7 removes the code paths guarded by `CUDA_HALF_INSTRUCTIONS` macro. Since the macro was removed in commit 2f186df, `ifdef CUDA_HALF_INSTRUCTIONS` would return false and hence the code path that is kept after this change is for the false case of `ifdef CUDA_HALF_INSTRUCTIONS`

- Commit 520c99b removes the code paths guarded by `CUDA_HALF_TENSOR` macro. Since Pytorch now provides support for only CUDA 8.0 and above, `CUDA_HALF_TENSOR` is always true since CUDA 8.0 satisfies `CUDA_HAS_FP16` and hence, the code path that is kept after this change is for the true case of `ifdef CUDA_HALF_TENSOR`.
Pull Request resolved: #10147

Differential Revision: D9345940

Pulled By: soumith

fbshipit-source-id: c9392261dd432d304f1cdaf961760cbd164a59d0

Summary:
This PR removes couple of macros throughout TH* as part of the re-factoring effort for ATen. Removing these macros should avoid confusion among developers who are trying to move things from TH* to ATen. This PR is part of the THCNumerics deprecation that I have been working on following up on mruberry's pytorch/pytorch#9318. I am separating these two commits to see if removal of these macros doesn't upset the pytorch public CI, as well as internal builds.

- Commit pytorch/pytorch@1248de7 removes the code paths guarded by `CUDA_HALF_INSTRUCTIONS` macro. Since the macro was removed in commit pytorch/pytorch@2f186df, `ifdef CUDA_HALF_INSTRUCTIONS` would return false and hence the code path that is kept after this change is for the false case of `ifdef CUDA_HALF_INSTRUCTIONS`

- Commit pytorch/pytorch@520c99b removes the code paths guarded by `CUDA_HALF_TENSOR` macro. Since Pytorch now provides support for only CUDA 8.0 and above, `CUDA_HALF_TENSOR` is always true since CUDA 8.0 satisfies `CUDA_HAS_FP16` and hence, the code path that is kept after this change is for the true case of `ifdef CUDA_HALF_TENSOR`.
Pull Request resolved: pytorch/pytorch#10147

Differential Revision: D9345940

Pulled By: soumith

fbshipit-source-id: c9392261dd432d304f1cdaf961760cbd164a59d0

Summary:
**Summary**: This PR is a followup of mruberry's #9318. It tries to achieve the following:
- Specializing std common math functions for `at::Half` type.
- Create `CUDANumerics.cuh` to contain necessary parts from `THCNumerics.cuh`.
- Update `THCNumerics.cuh` with new usage and comments to  demonstrate the best practice for developers and hence, making way for its deprecation.
- Remove legacy/redundant code path.
- Remove unused CUDA HALF macros (see separate PR #10147)

**Comments**: `CUDANumerics.cuh` contains mathematical functions that are either not in the std namespace or are specialized for compilation with CUDA NVCC or CUDA NVRTC. This header is derived from the legacy `THCNumerics.cuh`. Following are some rationale behind why some functions were kept while others were removed:
- All arithmetic can now be done in ATen using binary cuda kernel  or CUDA tensor pointwise apply (check #8919 and `CUDAApplyUtils`). `at::Half` comparisons rely on implicit conversion to float.
- Functions that are c/c++ standard compliant, have been specialized for user defined types, for instance, the std namespace has been opened up for `at::Half`, that defines math function definitions for `at::Half`. Check `Half-inl.h`
- Some standard compliant functions are specialized here for performance reasons. For instance, `powi` is used for `pow` calculation on integral types. Moreover, `abs`, `isinf`, `isnan` are specialized to save one API call vs when used with std. Although this is subject to change, depending on if we really care about saving one API call.
- Numeric limits such as `max/min` is removed since they call standard defines. Moreover, numeric limits for
`at::Half` is present in `Half-inl.h`. I understood that HIP has some issue with `std::numeric_limits` and this the related github issue I found: ROCm/hip#374. AlexVlx mentions that the issue can be avoided by launching `std::numeric_limits` in `__device__`. Since, we are launching lambdas with device contexts, I don't see an issue why `std::numeric_limits` won't compile on HIP if launched with device context within a kernel, unless I am not aware of the real reason why max/min was there in THCNumerics in the first place. (Haven't ever tried a build with HIP).

Here are some reference PRs that was handy in refactoring TH into ATen:
- #6786
- #5475
- #9401
- #8689
- #8919
Pull Request resolved: #10301

Differential Revision: D9204758

Pulled By: soumith

fbshipit-source-id: 09f489c1656458c02367b6cd31c3eeeca5acdc8a

Summary:
**Summary**: This PR is a followup of mruberry's pytorch/pytorch#9318. It tries to achieve the following:
- Specializing std common math functions for `at::Half` type.
- Create `CUDANumerics.cuh` to contain necessary parts from `THCNumerics.cuh`.
- Update `THCNumerics.cuh` with new usage and comments to  demonstrate the best practice for developers and hence, making way for its deprecation.
- Remove legacy/redundant code path.
- Remove unused CUDA HALF macros (see separate PR pytorch/pytorch#10147)

**Comments**: `CUDANumerics.cuh` contains mathematical functions that are either not in the std namespace or are specialized for compilation with CUDA NVCC or CUDA NVRTC. This header is derived from the legacy `THCNumerics.cuh`. Following are some rationale behind why some functions were kept while others were removed:
- All arithmetic can now be done in ATen using binary cuda kernel  or CUDA tensor pointwise apply (check pytorch/pytorch#8919 and `CUDAApplyUtils`). `at::Half` comparisons rely on implicit conversion to float.
- Functions that are c/c++ standard compliant, have been specialized for user defined types, for instance, the std namespace has been opened up for `at::Half`, that defines math function definitions for `at::Half`. Check `Half-inl.h`
- Some standard compliant functions are specialized here for performance reasons. For instance, `powi` is used for `pow` calculation on integral types. Moreover, `abs`, `isinf`, `isnan` are specialized to save one API call vs when used with std. Although this is subject to change, depending on if we really care about saving one API call.
- Numeric limits such as `max/min` is removed since they call standard defines. Moreover, numeric limits for
`at::Half` is present in `Half-inl.h`. I understood that HIP has some issue with `std::numeric_limits` and this the related github issue I found: ROCm/hip#374. AlexVlx mentions that the issue can be avoided by launching `std::numeric_limits` in `__device__`. Since, we are launching lambdas with device contexts, I don't see an issue why `std::numeric_limits` won't compile on HIP if launched with device context within a kernel, unless I am not aware of the real reason why max/min was there in THCNumerics in the first place. (Haven't ever tried a build with HIP).

Here are some reference PRs that was handy in refactoring TH into ATen:
- pytorch/pytorch#6786
- pytorch/pytorch#5475
- pytorch/pytorch#9401
- pytorch/pytorch#8689
- pytorch/pytorch#8919
Pull Request resolved: pytorch/pytorch#10301

Differential Revision: D9204758

Pulled By: soumith

fbshipit-source-id: 09f489c1656458c02367b6cd31c3eeeca5acdc8a

…rch#10301)

Summary:
**Summary**: This PR is a followup of mruberry's pytorch#9318. It tries to achieve the following:
- Specializing std common math functions for `at::Half` type.
- Create `CUDANumerics.cuh` to contain necessary parts from `THCNumerics.cuh`.
- Update `THCNumerics.cuh` with new usage and comments to  demonstrate the best practice for developers and hence, making way for its deprecation.
- Remove legacy/redundant code path.
- Remove unused CUDA HALF macros (see separate PR pytorch#10147)

**Comments**: `CUDANumerics.cuh` contains mathematical functions that are either not in the std namespace or are specialized for compilation with CUDA NVCC or CUDA NVRTC. This header is derived from the legacy `THCNumerics.cuh`. Following are some rationale behind why some functions were kept while others were removed:
- All arithmetic can now be done in ATen using binary cuda kernel  or CUDA tensor pointwise apply (check pytorch#8919 and `CUDAApplyUtils`). `at::Half` comparisons rely on implicit conversion to float.
- Functions that are c/c++ standard compliant, have been specialized for user defined types, for instance, the std namespace has been opened up for `at::Half`, that defines math function definitions for `at::Half`. Check `Half-inl.h`
- Some standard compliant functions are specialized here for performance reasons. For instance, `powi` is used for `pow` calculation on integral types. Moreover, `abs`, `isinf`, `isnan` are specialized to save one API call vs when used with std. Although this is subject to change, depending on if we really care about saving one API call.
- Numeric limits such as `max/min` is removed since they call standard defines. Moreover, numeric limits for
`at::Half` is present in `Half-inl.h`. I understood that HIP has some issue with `std::numeric_limits` and this the related github issue I found: ROCm/hip#374. AlexVlx mentions that the issue can be avoided by launching `std::numeric_limits` in `__device__`. Since, we are launching lambdas with device contexts, I don't see an issue why `std::numeric_limits` won't compile on HIP if launched with device context within a kernel, unless I am not aware of the real reason why max/min was there in THCNumerics in the first place. (Haven't ever tried a build with HIP).

Here are some reference PRs that was handy in refactoring TH into ATen:
- pytorch#6786
- pytorch#5475
- pytorch#9401
- pytorch#8689
- pytorch#8919
Pull Request resolved: pytorch#10301

Differential Revision: D9204758

Pulled By: soumith

fbshipit-source-id: 09f489c1656458c02367b6cd31c3eeeca5acdc8a