Closes the architect's tidy follow-up item on bench-number
methodology. The harness now accepts --runs N (default 1, byte-
identical output for back-compat); with N>=2 it reports
median + min..max per cell across runs, with N>=4 it drops the
slowest run before aggregating to match bench/run.sh's drop-
slowest throughput convention.
bench/run.sh now invokes the harness with --runs 5 for each of
the three latency arms, so a single bench/run.sh run produces
both a regression-stable throughput table and a regression-stable
latency table.
The qualitative claims from JOURNAL 2026-05-08 (RC tail latency
23x better than Boehm; RC RSS lower than Boehm) hold at the new
stat-of-5 confidence level — a 5-run smoke on the explicit-rc arm
shows p99=296µs (range 289-311), p99/median=1.31x (range 1.28-1.37).
Variance is well below the signal.
Resolves the architect's drift report on the 18g sub-arc:
- DESIGN.md: ratify mode-metadata's codegen role. param_modes /
ret_mode were already on Type::Fn since 18a; with 18d.4 / 18g
they became load-bearing for drop-emission decisions in
codegen. The new 'Mode metadata is load-bearing for codegen'
subsection records the four seams (Iter A + Iter B + 18g.1 +
18g.2) and names the let-alias-of-borrow carve-out the gates
do not propagate through.
- bench/run.sh: post-throughput, invoke bench/latency_harness.py
on the three canonical arms (Implicit @ gc, explicit @ rc,
Implicit @ rc control). The Boehm-retirement bench numbers
are now reproducible by anyone running the harness, not just
by hand on a specific host.
- Negative coverage: examples/rc_let_implicit_returning_app
+ alloc_rc_let_binder_for_implicit_returning_app_does_not_drop
pin the asymmetry to the (own)-ret-mode test (live=0 there,
live=1 here). The Borrow-ret-mode case is covered by the
language design itself — typechecker rejects 'borrow-
passthrough' shapes with consume-while-borrowed.
JOURNAL entry records four items as deferred known debt:
emit_inlined_partial_drop dynamic-tag fallback, carve-out
diagnostics surface, bench-number stat-of-N, and the
cross-family ordering observation about CLAUDE.md's tidy-iter
rule.
The 18-arc is formally closed with this tidy. Next iter is
the orchestrator's Boehm-retirement decision (Path A vs Path B
from JOURNAL 2026-05-08 18f entry, joined by the post-18g.2
re-bench numbers).
Adds rc to the modes list and an rc/bump ratio column in the
results table. The rc/bump ratio is the decisive number for
Decision 10's Boehm-retirement threshold (target 1.3x).
Adds --alloc=<gc|bump> to ail build/run. Bump path links a 256MB
no-free arena C stub instead of libgc; IR is byte-identical except
for the @GC_malloc → @bump_malloc symbol swap. Bench harness times
two allocation-heavy workloads (list cons/sum and balanced tree
build/walk) under both modes.
Numbers (RUNS=5, median of 4):
bench_list_sum gc 0.141s bump 0.048s +194%
bench_tree_walk gc 0.103s bump 0.041s +151%
Bucket: large. ~60% of runtime is Boehm on these workloads —
upper bound for any realistic program. Both fixtures hold the
heap fully live, so the cost we're seeing is Boehm's allocate
path itself, not collection work; that fact narrows the design
space for the GC discussion.
- crates/ailang-codegen: AllocStrategy enum, three callsites and
the IR header parameterised.
- crates/ail/src/main.rs: --alloc flag plumbed; bump runtime
located + compiled on demand.
- runtime/bump.c: 256MB static arena, abort-on-overflow.
- examples/bench_list_sum, bench_tree_walk: accumulator-form
fixtures (textbook recursive sum was constructor-blocked).
- bench/run.sh: harness with Python timing helper (Arch's
/usr/bin/time isn't part of the base install).
No language-level changes; default --alloc=gc, all 141 workspace
tests green, all 5 IR snapshots unchanged, 11 prior fixtures
produce identical stdout.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
Brummel