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El SDK CI - dev / build-and-test (pull_request) Failing after 12m7s
Implements the three primitives the test-framework design (DESIGN.md §6.5)
requires for gating on growth curves: el_alloc_count, el_alloc_bytes,
el_peak_rss. Registered in codegen's builtin_arity and wrapped in el_seed.c per
the project's C-builtin recipe.
WHY COUNTS AND NOT WALL-CLOCK: a growth-curve gate has to be a hard build
failure, which means the signal cannot flake. Wall-clock needs warmup,
statistics, and a quiet machine; on shared CI it is unusable as a gate.
Allocation counts are perfectly deterministic — same input, same number, every
machine, every run. Fit them against n and a complexity regression becomes a
build failure with zero noise.
All four runtime string allocators (el_strdup, el_strbuf, and their _persist
variants) funnel every allocation the language performs, so instrumenting there
counts everything.
WHY BYTES AS WELL AS COUNT — this is not redundancy, it is the whole gate.
Measured with two El programs, one allocating once per item, one rebuilding its
accumulator each iteration:
n linear allocs / bytes quadratic allocs / bytes
100 100 / 290 100 / 5,150
200 200 / 690 200 / 20,300
400 400 / 1,490 400 / 80,600
800 800 / 3,090 800 / 321,200
The quadratic program's allocation COUNT is exactly linear — identical to the
healthy one. Counting allocations alone would have missed it completely. Bytes
catch it: each doubling of n quadruples bytes (ratios 3.94, 3.97, 3.99 ->
converging on 4.0, i.e. O(n^2)), while the linear case converges on 2.0.
That shape — count linear, per-allocation size growing — is the classic
accidental quadratic, and it is exactly elc's defect: quadratic allocation
VOLUME, which the old shipped compiler paid in RSS (27 GB, OOM) and the rebuilt
one pays in malloc/free churn (42s on 1.4 MB). Volume was the invariant across
both; RSS and wall-clock were just the two ways it surfaced.
el_peak_rss is exported for context and is explicitly NOT a gating signal — it
is perturbed by allocator internals, the page cache, and the OS. Gate on the
deterministic numbers; report the physical one.
Counters are unsynchronised by design: this is measurement, and a lock would
change the thing being measured. Exact on the single-threaded compile path,
approximate under threads.