[Headers][X86] Allow SLLDQ/SRLDQ byte shift intrinsics to be used in constexpr

[RKSimon]

The SLLDQ/SRLDQ byte shift intrinsics can be used in constant expression

_mm_slli_si128 _mm256_slli_si256
_mm_srli_si128 _mm256_srli_si256

These will require handling inside VectorExprEvaluator::VisitCallExpr / InterpretBuiltin

NOTE: Ensure you handle out of bounds correctly

[kimyounhoex1]

Hi, I'd like to take this issue as my first LLVM contribution.

Thanks!

[NagrajMG]

I’ll handle the SLLDQ/SRLDQ intrinsic support implementation.

[RKSimon]

@NagrajMG More constexpr issues coming soon if there's nothing else in the list you want to do.

[kimyounhoex1]

@RKSimon @NagrajMG Thanks for assigning me this issue!
I’ll start looking into the code and update here with my progress.

[RKSimon]

Thanks - feel free to make a public branch / draft PR to show progress and if you're after any early feedback.

[llvmbot]

@llvm/issue-subscribers-backend-x86

Author: Simon Pilgrim (RKSimon)

The SLLDQ/SRLDQ byte shift intrinsics can be used in constant expression ``` _mm_slli_si128 _mm256_slli_si256 _mm_srli_si128 _mm256_srli_si256 ``` These will require handling inside VectorExprEvaluator::VisitCallExpr / InterpretBuiltin

NOTE: Ensure you handle out of bounds correctly

[llvmbot]

@llvm/issue-subscribers-clang-frontend

Author: Simon Pilgrim (RKSimon)

The SLLDQ/SRLDQ byte shift intrinsics can be used in constant expression ``` _mm_slli_si128 _mm256_slli_si256 _mm_srli_si128 _mm256_srli_si256 ``` These will require handling inside VectorExprEvaluator::VisitCallExpr / InterpretBuiltin

NOTE: Ensure you handle out of bounds correctly

[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.
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3. Fix the issue locally.
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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.

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