[Headers][X86] Allow SSE2/AVX2/AVX512F/AVX512BW/AVX512DQ integer arithmetic intrinsics to be used in constexpr

[RKSimon]

All of these intrinsics wrap generic implementations which can already be used in constexpr

_mm_add_epi8 _mm_add_epi16 _mm_add_epi32 _mm_add_epi64
_mm_sub_epi8 _mm_sub_epi16 _mm_sub_epi32 _mm_sub_epi64

_mm256_add_epi8 _mm256_add_epi16 _mm256_add_epi32 _mm256_add_epi64
_mm256_sub_epi8 _mm256_sub_epi16 _mm256_sub_epi32 _mm256_sub_epi64

_mm512_add_epi8 _mm512_add_epi16 _mm512_add_epi32 _mm512_add_epi64
_mm512_sub_epi8 _mm512_sub_epi16 _mm512_sub_epi32 _mm512_sub_epi64

(and avx512 mask/maskz variants)

You can use #152296 for reference

[llvmbot]

Hi!

This issue may be a good introductory issue for people new to working on LLVM. If you would like to work on this issue, your first steps are:

1. Check that no other contributor is working on this issue. If someone is assigned to the issue or claimed to be working on it, ping the person. After one week without a response, the assignee may be changed.
2. Leave a comment indicating that you are working on the issue, or just create a pull request after following the steps below. Mention this issue in the description of the pull request.
3. Fix the issue locally.
4. Run the test suite locally. Remember that the subdirectories under test/ create fine-grained testing targets, so you can e.g. use make check-clang-ast to only run Clang's AST tests.
5. Create a Git commit.
6. Run git clang-format HEAD~1 to format your changes.
7. Open a pull request to the upstream repository on GitHub. Detailed instructions can be found in GitHub's documentation. Mention this issue in the description of the pull request.

If you have any further questions about this issue, don't hesitate to ask via a comment in the thread below.

[llvmbot]

@llvm/issue-subscribers-good-first-issue

Author: Simon Pilgrim (RKSimon)

All of these intrinsics wrap generic implementations which can already be used in constexpr ``` _mm_add_epi8 _mm_add_epi16 _mm_add_epi32 _mm_add_epi64 _mm_sub_epi8 _mm_sub_epi16 _mm_sub_epi32 _mm_sub_epi64 _mm_mullo_epi16 _mm_mullo_epi32

_mm256_add_epi8 _mm256_add_epi16 _mm256_add_epi32 _mm256_add_epi64
_mm256_sub_epi8 _mm256_sub_epi16 _mm256_sub_epi32 _mm256_sub_epi64
_mm256_mullo_epi16 _mm256_mullo_epi32

_mm512_add_epi8 _mm512_add_epi16 _mm512_add_epi32 _mm512_add_epi64
_mm512_sub_epi8 _mm512_sub_epi16 _mm512_sub_epi32 _mm512_sub_epi64
_mm512_mullo_epi16 _mm512_mullo_epi32
_mm_mullo_epi64 _mm256_mullo_epi64 _mm512_mullo_epi64

(ignore the AVX512 mask/maskz variants for now)

You can use https://github.com/llvm/llvm-project/pull/152296 for reference
</details>

[llvmbot]

@llvm/issue-subscribers-backend-x86

Author: Simon Pilgrim (RKSimon)

All of these intrinsics wrap generic implementations which can already be used in constexpr ``` _mm_add_epi8 _mm_add_epi16 _mm_add_epi32 _mm_add_epi64 _mm_sub_epi8 _mm_sub_epi16 _mm_sub_epi32 _mm_sub_epi64 _mm_mullo_epi16 _mm_mullo_epi32

_mm256_add_epi8 _mm256_add_epi16 _mm256_add_epi32 _mm256_add_epi64
_mm256_sub_epi8 _mm256_sub_epi16 _mm256_sub_epi32 _mm256_sub_epi64
_mm256_mullo_epi16 _mm256_mullo_epi32

_mm512_add_epi8 _mm512_add_epi16 _mm512_add_epi32 _mm512_add_epi64
_mm512_sub_epi8 _mm512_sub_epi16 _mm512_sub_epi32 _mm512_sub_epi64
_mm512_mullo_epi16 _mm512_mullo_epi32
_mm_mullo_epi64 _mm256_mullo_epi64 _mm512_mullo_epi64

(ignore the AVX512 mask/maskz variants for now)

You can use https://github.com/llvm/llvm-project/pull/152296 for reference
</details>

[keyvchan]

@RKSimon hi, I would like to try out this. Can I be assigned?