Blog publication task for PR #1215

Source: #1215
Merged commit: 419226c9df5997f57b7a54eaed6e8a8201a54095

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One opcode bit made two identical vectors look opposite

DRAFT — Merged PR; unpublished blog draft

PR: #1215

Head SHA: acaad5eeef91846f921eea84eaff50198231830d

This file is an unpublished artifact, not an instruction to an agent.

Merged PR; unpublished blog draft. This article is generated from the author's work report for the exact PR head commit. Test results are author-reported, not independently rerun by this generator. Merge status is not proof of deployment or runtime correctness.

Work report

The ARM64 JIT computed wrong bundles and cosines and the VM drew one random vector for every seed; both are fixed, the tests that had been bent around them assert the right values again, and the profile now runs on aarch64 as well as x86_64.

What changed

• Fixed two encodings in src/jit_arm64.zig: CMGT #0 was emitted as CMLT #0, and LDRSB loaded into W under 64-bit tail arithmetic.
• Added differential tests against a scalar reference to src/jit_arm64.zig, src/jit_x86_64.zig and src/jit.zig, over random trits and dimensions with and without a tail; each skips off its own architecture.
• Made v_random use its seed, mapped the fused cosine's 0/0 to 0, and restored the VM and e2e assertions that had disabled the JIT or taken the absolute value of the cosine.
• Made the headless floors per architecture and ran the profile on ubuntu-24.04-arm as well as ubuntu-latest.

Context and reasoning

The symptom: the VM said cos(v, v) = -1.0, and the tests had been relaxed to accept it.

The causes: two ARM64 encodings and a seed that was never read, found by testing every kernel against a scalar reference.

The gate: differential tests that skip off their architecture, floors per architecture, and an ARM64 runner.

Reported verification

• [passed] Command: zig test src/jit_arm64.zig on Linux aarch64. Result: 25 of 25 tests, including the differential test; with CMLT restored it reports bundle_simd wrong at every dimension, with LDRSB Wt restored it reports cosine and bundle tails wrong.. Evidence: Ubuntu 24.04 aarch64 container, Zig 0.15.2, run locally before the commit
• [passed] Command: zig test src/jit_x86_64.zig and src/jit.zig -target x86_64-linux-gnu, run in an amd64 container. Result: 6 of 6 and 7 of 7 tests; a planted setg/setl swap in jit.zig makes the differential test report bundle wrong at nine dimensions.. Evidence: Run locally under emulation before the commit
• [passed] Command: python3 tools/reproduce.py headless --zig zig-0.15.2 in ubuntu:24.04 aarch64 with empty caches. Result: Build 94/94 with 46/46 installs; test 135/135 steps, 2763/2776 passed and 13 skipped, 66 run steps with tests and one empty, no compile failure, both commands exit 0; no violation against the aarch64 floors.. Evidence: Linux aarch64 container, head acaad5e, fresh zig caches, 2 min 36 s

Limits and open questions

• The x86_64 floors (2773 passed, 3 skipped) are derived from the counts of the added tests and the previous x86_64 run; this PR's x86_64 job measures them.
• Most older tests in src/jit_arm64.zig and src/jit_x86_64.zig still return early off their architecture and count as passed; the new differential tests skip instead.
• The aarch64 leg depends on GitHub's ubuntu-24.04-arm runners.

Receipts

• gHashTag/trinity PR #1215
• Reported head commit acaad5eeef91
• Merge commit 419226c9df59

Topic tags

#Engineering #Verification #CI