shoney.arickathil
79605cbb4f
- `woc` now emits `.wob` that `wovm` runs: emit.ml lowers the typed, owner-annotated AST (scope-stack registers with a >64 WO-E401 diagnostic, Lua-style call windows, ICALL by slot, dedup const pool, drop maps, line tables, implicit terminators); disasm.ml backs `--dump-bc` goldens. - Ownership lowering consumes the four owner tables verbatim; RESIDUAL is the only source of borrow ops, coalesced per operand. Review caught the emitter consuming only 2 of owner.ml's 4 residual producers — an assignment-anchored aliasing violation ran to exit 0 instead of trapping; fixed, plus a backstop raising WO-E404 for any residual region left unconsumed. - Conformance harness `scripts/oop-e2e.sh` (`just oop-e2e`): four fixture kinds with exact outcomes — byte-exact stdout, one WO-E### anchored on `error CODE:`, numeric trap code, gc trace. 25 fixtures incl. pricing-demo logic, the ownership suite, and DB_STUB's parse-but-trap. `tests/` un-ignored so the corpus is actually tracked. - `woc build` produces a self-contained binary: wovm copy + appended image + 20-byte trailer, self-exec via /proc/self/exe. Verified relocated outside the repo, argless, and against adversarial trailer corruption. - Milestone 1's five spec criteria all MET (`just oop-accept`). Criterion 3 closed by WO-E405 — the entry must return `Int`, since program mode already says its return value is the exit code — which deletes the leak class without adding return-type metadata to the format. `gc/held-cycle` retired: an externally-held cycle is not expressible in a post-exit pump. - New spec: inferred GC + incremental per-shard tri-color mark-sweep, retiring `@gc` and reference counting. Story gains iterations 7b (that work) and 9b (`@table`, relations, compiler-checked query); `.dev/reference` gains a sparse System.Linq checkout. Priority: 5→6→7 (log-watcher) then 7b, 8, 9, 9b.
108 lines
5.6 KiB
Markdown
108 lines
5.6 KiB
Markdown
# Iteration 7b — inferred GC + incremental mark-sweep
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> Format: `product/story-iteration-template`. Part of
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> [Story — one language, one runtime, one database, one binary](00-story.md).
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>
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> **Inserted 2026-08-11**, after the plan was first drawn — hence `7b` rather
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> than a renumber. It sits here because the log-watcher critical path
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> (iterations 3–7) must not be delayed, and because the collector should be
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> settled before iteration 8 multiplies shards.
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## Goals
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- **The developer stops deciding which types are garbage collected.** `@gc`
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disappears from the language; the compiler infers GC-ness and reports every
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decision with its reason.
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- Reference counting is replaced by an incremental per-shard tri-color
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mark-sweep collector, so the compiler no longer has to emit a balanced
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acquire/release at every alias site — the source of every recorded `@gc`
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defect.
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- Milestone 1's acceptance criterion 3 (ASan-clean across the corpus) closes,
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because the leak blocking it is one of the defects this deletes.
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## Acceptance Criteria
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- What to achieve?
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- **Given** a class whose declaration can form a reference cycle, and a
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separate class that is only ever shared through a long-lived alias,
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- **when** the program is compiled,
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- **then** both are classified GC-managed without any annotation, and
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`--dump-gc` names the reason for each — a cycle path for the first, the
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escaping alias site for the second.
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- What to achieve?
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- **Given** any `.wo` source containing `@gc`,
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- **when** it is compiled,
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- **then** it is a diagnostic pointing at inference and `--dump-gc`, not a
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silently accepted no-op.
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- What to achieve?
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- **Given** a program that hides a traced object from the collector —
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storing it into an already-blackened object between marking slices and
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dropping the original reference,
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- **when** the collector completes,
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- **then** the object is still alive; and the same fixture fails loudly if
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the write barrier is compiled out.
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- What to achieve?
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- **Given** an abandoned cycle and a cycle still rooted from a live frame,
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- **when** collection runs,
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- **then** the abandoned one is freed within budgeted slices with no slice
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exceeding the configured budget, and the rooted one survives.
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- What to achieve?
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- **Given** the whole conformance corpus, run repeatedly so several
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collection cycles occur,
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- **when** it runs under ASan,
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- **then** zero leaks and zero errors — the clause that currently fails.
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- What to achieve?
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- **Given** any emitted `.wob` image,
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- **when** it is disassembled,
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- **then** no `RC_INC` or `RC_DEC` appears, and the format doc records
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opcodes 27–28 as reserved behind a version bump.
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## Out Of Scope
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- Cross-shard tracing — ownership moves mean no traced object spans shards.
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- Generational collection and compaction. Non-moving is load-bearing: no
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forwarding pointers, no read barrier. Go's collector is not generational
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either.
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- Scheduler-integrated pacing beyond the heap-goal trigger; that stays
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iteration 8's concern, which is part of why this lands first.
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- `ref T` semantics, unchanged — it is an id, not a pointer, and creates no
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edge in the inference graph.
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## Info
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- Governing spec: [`docs/superpowers/specs/2026-08-11-inferred-gc-mark-sweep-design.md`](../../superpowers/specs/2026-08-11-inferred-gc-mark-sweep-design.md).
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- **Why the annotation was insufficient, not merely inconvenient:** the OOP
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spec's own example, `@gc class PriceCache { entries: map<SKU, Money> }`, is
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acyclic. It needs GC because it is shared, and second-class borrows cannot
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be stored or returned. So the developer was being asked to reason about type
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shape *and* whole-program aliasing at once — hence the hybrid rule
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(structural SCC plus reported demand promotion).
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- **Why tracing rather than better reference counting:** all four recorded
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`@gc` defects are RC bookkeeping failures — `push` missing an increment,
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`set` still missing one, the `mut`-`@gc` clobber, and the held-cycle leak.
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Inferring GC-ness would widen that population and so widen that bug class.
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Tracing emits no per-alias bookkeeping at all.
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- **Most of what tracing needs already exists.** The emitter already produces
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precise per-pc pointer masks (the drop table's gc mask) and the class table
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already carries per-field kinds — the two pieces Go gets from stack maps and
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type maps. Go's dependence on OS threads is incidental; the algorithm needs
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only per-frame PC→map lookup and the ability to suspend one stack.
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- **The one real runtime addition:** the arena cannot enumerate objects — bump
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allocation plus size-class free lists, with large objects on bare `malloc`
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and no size headers anywhere. Sweep needs its own list. Retiring `rc`, plus
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the `borrow` word that traced objects never use, frees exactly eight
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contiguous bytes for an intrusive link, so the 16-byte header survives.
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- This iteration **supersedes part of iteration 2's memory model** (§4 of the
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OOP spec) and closes iteration 4's open gate clause. Neither is renumbered;
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both carry pointers here.
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## Proposed Solution
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- Write the implementation plan from the approved spec, then execute it: the
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`gcinfer.ml` pass (Tarjan SCC over the class-reference graph, then demand
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promotion to a fixpoint, with a note per decision), the `@gc` removal and
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its diagnostic, retiring `RC_INC`/`RC_DEC` and the rc machinery from
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`owner.ml`/`emit.ml`, the per-shard traced list and sweep, incremental
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tri-color marking with roots read from the existing pc masks, the Yuasa
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deletion barrier inside the VM's store paths, and the doc/golden migration
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the spec's §8 table enumerates.
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