Brummel
ae2eb2efac
18d.4 Iter A (arm-close pattern-binder dec) and Iter B (Own-param
dec at fn return) both fire AFTER the arm body lowers; for a tail-
call arm body, lower_term emits 'musttail call ... ret' and sets
block_terminated=true, so neither seam fires. The result: the
scrutinee's outer cell (whose ptr fields were all moved into the
tail-call's args via 18d.3 moved_slots) leaks one cell per
recursion step.
Surfaced by 18f.2's tail-latency bench: explicit-mode RC peaked
at the same 511 MB RSS as implicit-mode RC despite full mode
annotations — the per-op IntList chains were never being freed.
Bencher diagnosed the tail-call drop-elision; this iter implements
the fix.
Fix shape: in lower_match, BEFORE lower_term(arm.body), emit
'call void @ailang_rc_dec(ptr <scrutinee_ssa>)' iff:
- alloc=Rc,
- arm.body is structurally Term::App{tail:true} or
Term::Do{tail:true},
- scrutinee_is_owned (existing 18d.4 Iter A gate, hoisted),
- every ptr-typed slot in this ctor's pattern is in
moved_slots[scrutinee] (i.e. all ptr children are moved into
binders that own them downstream — a Wild-bound ptr would
still hold a live ref that the shallow free would strand).
Shallow rc_dec, not field_drop_call: the per-type drop fn would
re-walk ptr fields, dec'ing values now owned by the downstream
frame — exactly the bug 18d.3's moved_slots was set up to prevent.
Hoists scrutinee_is_owned to a single declaration shared by both
the new 18g.1 emission and 18d.4 Iter A.
Red: alloc_rc_explicit_mode_tail_sum_does_not_leak_outer_cells
on examples/rc_tail_sum_explicit_leak — 100 LCons cells leaked
pre-fix, 0 post-fix. Verified end-to-end on
bench_latency_explicit: pre-fix live=11068575,
post-fix live=1048575 (= the persistent tree cache, separate
issue at main-scope-close).
Test infrastructure: build_and_run_with_rc_stats helper +
AILANG_RC_STATS=1 env-var for the runtime atexit summary.