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Claude 7c3c59f5f8 phase0: dry run — comrak & tokei vendored, 3 attempts in ledger

Target selection (SPEC §6): comrak 0.53.0 (45c1995, BSD-2-Clause) and
tokei 14.0.0 (fa44e51, MIT/Apache-2.0); both CPU-bound with pinned
corpora (progit book 11MB; 8x replicated pinned trees, 221MB) and
committed MANIFEST.sha256 + golden-output pins + regen scripts.

Calibration: A/A null verdicts on both real workloads; taskset -c 2
pinning tightens the A/A CI from [0.938, 1.008] to [0.993, 1.008],
making the 2% accept threshold meaningful in this container.

Profiles (callgrind; perf unavailable): comrak allocator symbols 26.7%
of Ir; tokei perform_multi_line_analysis 31.7%.

Attempts (ledger + results/phase0/):
- comrak class-1 target-cpu=native: null [0.983, 1.011], rejected-bench
- comrak class-2 mimalloc swap: +4.6% [1.033, 1.058], 848 upstream
  tests green, golden byte-identical, ASan-proper clean; LSan flags
  484B in onig (reachability false-positive analysis in case study) ->
  needs-human-review per SPEC §8
- tokei class-1 fat LTO+cgu=1: +1.6% [1.003, 1.026], real but under
  the 2% bar, rejected-bench

Also: ledger-cli for manual rows, targets/ excluded from trust-layer
workspace, corpora/build artifacts gitignored, case study written.
Phase 0 exit criteria (>=10% verified win) not yet met; next
hypotheses logged in results/phase0/attempts.md.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01EcKPWQ3MQD4NdEHwar96u2

2026-07-06 19:28:50 +00:00

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Phase 0 dry-run attempt log

Hypotheses are recorded here before any patch is applied; final evidence and verdicts go to the SQLite ledger and are mirrored here.

Environment for the whole session: remote 4-core container (Intel Xeon @ 2.10GHz, kernel 6.18.5), governor/turbo not controllable, benches pinned with taskset -c 2. A/A calibration on both target workloads passed with pinning (see results/calibration/).

Deviations from SPEC (Phase 0 manual dry run)

No nested no-network container available (no docker daemon): target code runs in this session's own isolated ephemeral container, which serves as the sandbox. Phase 1 must restore the dedicated container.
perf unavailable (container): profiling via valgrind/callgrind (deterministic instruction counts, Ir), not cycle sampling. Ir% is a proxy for cycles%; it under-weights cache/branch effects.
Corpus files >10 MB are pinned by committed MANIFEST.sha256 + regeneration scripts rather than committed raw (repo bloat).

Attempt 1 — comrak, class 1 (build configuration)

Logged: 2026-07-06, before patching.
Hotspot: whole-program; upstream already ships lto=true + codegen-units=1, so classic class-1 flags are exhausted upstream.
Hypothesis: RUSTFLAGS=-C target-cpu=native (baseline ISA: the bench machine's Xeon) enables wider SIMD paths in string scanning (jetscii, memchr paths visible in profile) and better scheduling; expect a small win, 2-6% median speedup. No FP semantics change (integer/string workload; not a -ffast-math-class flag), so auto-acceptable if gates pass. Deploy caveat: win only valid for fleets whose ISA baseline matches; recorded in workload statement.
Patch: none (env-level build config); candidate built to a separate CARGO_TARGET_DIR from the same pinned commit.

Attempt 2 — comrak, class 2 (allocator swap)

Logged: 2026-07-06, before patching, after Attempt 1's hypothesis.
Hotspot: allocator symbols sum to ~26.7% of Ir (_int_malloc 9.99%, _int_free 6.85%, malloc 3.92%, malloc_consolidate 3.48%, free 2.49%) — the class-2 precondition (≥5%) is exceeded 5x.
Hypothesis: glibc malloc is the allocator; comrak's AST/inline parsing churns small allocations. Swapping the CLI's global allocator to mimalloc cuts allocator instructions substantially; expect 8-20% median speedup on the progit workload.
Patch plan: 2-line change in comrak CLI main + Cargo.toml dep, inside targets/comrak/workspace only.

Attempt 3 — tokei, class 1 (build configuration)

Logged: 2026-07-06, before patching.
Hotspot: whole-program; upstream ships lto="thin", panic="abort", default codegen-units (16).
Hypothesis: lto=true (fat) + codegen-units=1 lets the analysis loop (perform_multi_line_analysis, 31.7% Ir) inline across cgu and crate boundaries (memchr/aho-corasick calls visible in profile); expect 2-8% median speedup. No semantics change; auto-acceptable if golden replay passes.
Patch: [profile.release] lto = true, codegen-units = 1 in targets/tokei/workspace/Cargo.toml only.

Outcomes (ledger is authoritative: results/ledger.sqlite)

run_id	class	speedup median	95% CI	verdict
phase0-comrak-001	1 build-config	0.9965	[0.9826, 1.0110]	rejected-bench (null)
phase0-comrak-002	2 allocator	1.0459	[1.0333, 1.0577]	needs-human-review
phase0-tokei-001	1 build-config	1.0161	[1.0026, 1.0262]	rejected-bench (< 2% threshold)

comrak-002 gates: 848 upstream tests green on patched tree; golden replay byte-identical; pristine ASan+LSan clean; patched ASan-proper clean; LSan flags 484 B in onig (analysis: LSan × custom-allocator reachability false positive — see case-study-comrak.md). SPEC §8 routes any sanitizer flag to human review, so that is the verdict.
tokei-001 is a real but small effect — CI excludes 1.0 but its lower bound (+0.26%) is under the 2% bar. Correctly rejected; logged so nobody re-grinds it.
Phase 0 exit criteria (≥1 verified win ≥10%) not yet met: best verified candidate is +4.6% pending human review. Next cheapest hypotheses per profile: comrak class 3 (allocation churn — arena the inline parser's Vec growth, RawVec::finish_grow 2.3% + memcpy 3.1%); tokei class 3 (memset 8.5% suggests per-file buffer zeroing) and class 5 (perform_multi_line_analysis 31.7% single frame).

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