<table border="1" cellspacing="0" cellpadding="8">
    <tr>
        <th>Issue</th>
        <td>
            <a href=https://github.com/llvm/llvm-project/issues/154283>154283</a>
        </td>
    </tr>

    <tr>
        <th>Summary</th>
        <td>
            [Headers][X86] VectorExprEvaluator::VisitCallExpr - allow SSE/AVX2/AVX512 pack intrinsics to be used in constexpr
        </td>
    </tr>

    <tr>
      <th>Labels</th>
      <td>
            good first issue,
            backend:X86,
            clang:frontend,
            clang:headers,
            constexpr
      </td>
    </tr>

    <tr>
      <th>Assignees</th>
      <td>
      </td>
    </tr>

    <tr>
      <th>Reporter</th>
      <td>
          RKSimon
      </td>
    </tr>
</table>

<pre>
    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.
</pre>
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