Brummel
2488d9d345
After the leg-1 fix (68f500c), a tail call wrapped in a trailing
`(let ...)` (or `seq`) still leaks: the arm body is an MTerm::Let, not
a direct App{tail:true}, so `arm_body_is_tail_call` (match_lower.rs
~717) is false and both the scrutinee-husk shallow-dec and the leg-1
owned-param dec are skipped — while lower_term still descends through
the Let body and emits the inner call as musttail. The scrutinee husk
and the non-forwarded owned param each leak one slab per recursion
step.
Series-free minimal repro (a plain `Box` whose replacement is
let-bound before the tail call), asserting live == 0 under
AILANG_RC_STATS=1. RED today: `allocs=6 frees=2 live=4`. This is the
leg that keeps examples/series_sma.ail at live=8 (its canonical
`(let s_new (push …) (seq … (tail-app …)))` body).
The debugger confirmed the fix is contained, not a design fork:
`arm_body_is_tail_call` feeds only the two drop-emission gates, never
the musttail-emission decision (which lives independently in
lower_term off App{tail:true}), so peeling the detection through a
trailing Let/Seq chain ending in a tail call is safe. The let
scope-close drop is gated on `!block_terminated` and so is correctly
skipped, avoiding a double-free of the let binding.
refs #63
19 lines
721 B
Plaintext
19 lines
721 B
Plaintext
(module tail_recur_let_wrapped_no_leak_pin
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(data Box (ctor B (con Int)))
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(data IntList (ctor INil) (ctor ICons (con Int) (con IntList)))
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(fn run
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(type (fn-type (params (own (con Box)) (own (con IntList))) (ret (own (con Unit))) (effects IO)))
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(params b input)
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(body
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(match input
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(case (pat-ctor INil) (do io/print_str "done\n"))
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(case (pat-ctor ICons v rest)
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(let b_new (term-ctor Box B v)
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(tail-app run b_new rest))))))
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(fn main
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(type (fn-type (params) (ret (own (con Unit))) (effects IO)))
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(params)
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(body
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(let b (term-ctor Box B 0)
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(app run b (term-ctor IntList ICons 1 (term-ctor IntList ICons 2 (term-ctor IntList INil))))))))
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