llvm/llvm-project

[Clang] VectorExprEvaluator::VisitCallExpr / InterpretBuiltin - add MMX/SSE/AVX/AVX512 VPSADBW intrinsics to be used in constexpr

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#188,062 opened on Mar 23, 2026

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backend:X86clang:bytecodeclang:frontendconstexprgood first issue

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Description

The horizontal sum of difference intrinsics can all be used in constexpr with suitable handling of the builtins inside VectorExprEvaluator::VisitCallExpr and InterBuiltin.cpp, and testing in the relevent *-builtins.c files.

_mm_sad_epu8 _mm256_sad_epu8 _mm512_sad_epu8 _mm_sad_pu8

Care needs to be taken with the signed/unsigned extension of the arguments - we might need to adjust the builtin signatures.

Review other sub-issues from #30794 on implementation

Split off from #157522

Contributor guide

Research direction
Study existing horizontal add implementations in VectorExprEvaluator and InterpretBuiltin, then replicate for VPSADBW variants. Adjust builtin signatures for signed/unsigned extension as needed. Refer to sub issues in #30794 for implementation details.
Tech stack
None
Domain
backend
Issue type
Feature
DifficultyEstimated implementation difficulty for a new contributor, from 1 for very small changes to 5 for expert-level work.
3
Estimated timeA rough time range for an experienced contributor to investigate, implement, test, and prepare a pull request.
1-2 days
Activity statusHow available the issue appears right now: fresh, active, stale, blocked, or waiting on maintainer input.
Active
ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.
Mostly clear
Prerequisites
C++Clang/LLVM internalscompiler development
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
30