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.
70 lines
1.8 KiB
Plaintext
70 lines
1.8 KiB
Plaintext
; Iter 18g.1 RED-test fixture: minimal tail-recursive list-sum
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; under explicit-mode + (drop-iterative). Demonstrates the leak
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; surfaced by the 18f.2 latency bench: the LCons outer cell, whose
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; only ptr field `t` is moved into the tail-app of `sum_acc`, has
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; no drop site and leaks once per element.
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;
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; Built and run with `AILANG_RC_STATS=1` under `--alloc=rc`. The
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; stderr summary should show `allocs == frees + small_const`,
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; where `small_const` covers the Tree-shaped drop-frames (zero
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; here — the program returns Int, no live ADTs at exit).
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;
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; Pre-fix: `live = N` (one outer LCons cell per consumed element).
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; Post-fix: `live = 0`.
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(module rc_tail_sum_explicit_leak
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(data IntList
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(ctor LNil)
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(ctor LCons (con Int) (con IntList))
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(drop-iterative))
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(fn cons_n_acc
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(type
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(fn-type
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(params (con Int) (own (con IntList)))
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(ret (own (con IntList)))))
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(params n acc)
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(body
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(if (app == n 0)
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acc
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(tail-app cons_n_acc
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(app - n 1)
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(term-ctor IntList LCons (app - n 1) acc)))))
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(fn cons_n
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(type
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(fn-type
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(params (con Int))
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(ret (own (con IntList)))))
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(params n)
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(body
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(app cons_n_acc n (term-ctor IntList LNil))))
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(fn sum_acc
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(type
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(fn-type
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(params (own (con IntList)) (con Int))
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(ret (con Int))))
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(params xs acc)
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(body
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(match xs
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(case (pat-ctor LNil) acc)
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(case (pat-ctor LCons h t)
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(tail-app sum_acc t (app + acc h))))))
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(fn sum_list
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(type
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(fn-type
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(params (own (con IntList)))
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(ret (con Int))))
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(params xs)
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(body
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(app sum_acc xs 0)))
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(fn main
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(type (fn-type (params) (ret (con Unit)) (effects IO)))
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(params)
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(body
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(do io/print_int (app sum_list (app cons_n 100))))))
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