[Headers][X86] VectorExprEvaluator::VisitCallExpr - allow SSE/AVX2/AVX512 pack intrinsics to be used in constexpr

[RKSimon]

Handle the saturated truncation intrinsics inside VectorExprEvaluator::VisitCallExpr and add constexpr test coverage, similar to #152524

_mm_packs_epi16  _mm256_packs_epi16  _mm512_packs_epi16  _mm_packs_pi16
_mm_packs_epi32  _mm256_packs_epi32  _mm512_packs_epi32  _mm_packs_pi32

_mm_packus_epi16 _mm256_packus_epi16 _mm512_packus_epi16 _mm_packs_pu16
_mm_packus_epi32 _mm256_packus_epi32 _mm512_packus_epi32

(plus the AVX512BW mask/maskz variants)

Note that these are slightly more complex than regular elementwise intrinsics as the 2 operands are packed together at the 128-bit level.

[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:

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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)

Handle the saturated truncation intrinsics inside VectorExprEvaluator::VisitCallExpr and add constexpr test coverage, similar to #152524 ``` _mm_packs_epi16 _mm256_packs_epi16 _mm512_packs_epi16 _mm_packs_pi16 _mm_packs_epi32 _mm256_packs_epi32 _mm512_packs_epi32 _mm_packs_pi32

_mm_packus_epi16 _mm256_packus_epi16 _mm512_packus_epi16 _mm_packs_pu16
_mm_packus_epi32 _mm256_packus_epi32 _mm512_packus_epi32

(plus the AVX512BW mask/maskz variants)

Note that these are slightly more complex than regular elementwise intrinsics as the 2 operands are packed together at the 128-bit level.
</details>

[llvmbot]

@llvm/issue-subscribers-backend-x86

Author: Simon Pilgrim (RKSimon)

Handle the saturated truncation intrinsics inside VectorExprEvaluator::VisitCallExpr and add constexpr test coverage, similar to #152524 ``` _mm_packs_epi16 _mm256_packs_epi16 _mm512_packs_epi16 _mm_packs_pi16 _mm_packs_epi32 _mm256_packs_epi32 _mm512_packs_epi32 _mm_packs_pi32

_mm_packus_epi16 _mm256_packus_epi16 _mm512_packus_epi16 _mm_packs_pu16
_mm_packus_epi32 _mm256_packus_epi32 _mm512_packus_epi32

(plus the AVX512BW mask/maskz variants)

Note that these are slightly more complex than regular elementwise intrinsics as the 2 operands are packed together at the 128-bit level.
</details>

[llvmbot]

@llvm/issue-subscribers-clang-frontend

Author: Simon Pilgrim (RKSimon)

Handle the saturated truncation intrinsics inside VectorExprEvaluator::VisitCallExpr and add constexpr test coverage, similar to #152524 ``` _mm_packs_epi16 _mm256_packs_epi16 _mm512_packs_epi16 _mm_packs_pi16 _mm_packs_epi32 _mm256_packs_epi32 _mm512_packs_epi32 _mm_packs_pi32

_mm_packus_epi16 _mm256_packus_epi16 _mm512_packus_epi16 _mm_packs_pu16
_mm_packus_epi32 _mm256_packus_epi32 _mm512_packus_epi32

(plus the AVX512BW mask/maskz variants)

Note that these are slightly more complex than regular elementwise intrinsics as the 2 operands are packed together at the 128-bit level.
</details>

[woruyu]

Hello, I would like to work for it!