simd-vectorization

name	simd-vectorization
description	Implement issue

SIMD Vectorization

Use this skill to execute issue #86 in incremental phases with correctness-first behavior.

Workflow

1. Baseline scalar correctness for vector IR at O0.
2. Add target feature gating API (TargetFeatures) in x86 backend.
3. Implement SSE4.2 lowering for common vector patterns.
4. Extend to AVX2 where supported.
5. Add vector end-to-end test (.ll -> object -> link -> run).

Step 1: Scalar Baseline

• Ensure ExtractElement, InsertElement, and ShuffleVector do not panic.
• For unsupported vector ops, lower to conservative scalar fallback or deterministic zero/stub behavior with explicit comments.
• Add tests proving lowering is non-panicking for every vector InstrKind variant.

Step 2: Feature Gating

• Introduce x86 TargetFeatures with at least sse42 and avx2 flags.
• Default behavior should be conservative (disabled unless explicitly enabled).
• Gate SIMD instruction emission on features; fallback path must remain correct.

Step 3: SSE4.2 First

• Implement 128-bit lowering for most common integer and float vector arithmetic.
• Add encoding tests per opcode family in llvm-target-x86/src/encode.rs tests.
• Keep mapping explicit; avoid silent fallback to unrelated opcodes.

Step 4: AVX2 Follow-up

• Extend lowering to 256-bit forms for the same opcode families.
• Reuse feature-gated selector logic; avoid duplicating correctness code.

Step 5: Validation

Run at minimum:

cargo +stable test -p llvm-target-x86
cargo +stable test -p llvm-ir-parser
cargo +stable test

If native link/run smoke cannot execute in environment, document exact blocker and include parser/codegen-only evidence.

Step 6: Review + Full Test

• Review implementation PR with focus on codegen correctness, gating behavior, and fallback safety.
• Run targeted checks and full suite (cargo +stable test) unless blocked.

Step 7: Issue+Fix Loop (Same PR)

• If concrete problems are found, open GitHub issue(s) documenting each.
• Fix findings in the same PR branch and push follow-up commits.

Step 8: Post Review Summary

• Post PR review feedback (gh pr review --comment or gh pr comment) summarizing findings and fixes.
• Include issue links in the PR review summary.

Resources

• Use references/issue-86-plan.md for acceptance checklist and sequencing.
• Use scripts/vector_opcode_audit.sh to scan vector-op coverage and TODO sites.