# Session 2026-10-24 — separate compilation (core)

V3 now builds per-unit objects.  The one-shot mode remains the default
for the suite/corpus.

**Branch:** `master`.  **Feature state:** `v3-separate-compilation`.
**Gates:** suite **305/305**, fixpoint **OK (3,807,056 bytes)**,
corpus **519/612 compile-OK, 0 crashes**.

---

## What shipped

- **Stable symbols**
  - module procedure: `<Module>__<name>`
  - module global: `<Module>_<name>`
  - string/ctor/set pools: `<Module>_strN`, `<Module>_ctoN`,
    `<Module>_setN`
  - class vtable: `<Module>__<Class>__vt`; methods include their class
  - nested procedures: object-local module-prefixed uid
  - external C procedures: C link name unchanged
- **Per-unit codegen**
  - `M2 -c Target.mod` emits one `.ssa`; the target's own `.def` is
    found beside it automatically.
  - Library objects have **no `main`**; the program object has the
    only `main`.
  - Every object exports `<Module>_init`, including modules with no
    `BEGIN` body; the program calls imported inits in dependency order.
  - Top-level data is `export data`, so imported globals resolve.
- **Driver**
  - `M2 -c` lowers the target `.mod` and its own `.def` (for exported
    data), skips imported definition units, and records imported init
    calls.
  - `M2make --separate` scans imports transitively, compiles each unit
    to `gen_ssa/<Module>.o`, and links all objects with `cc` + shim.
- **Classes**
  - stable vtable/method symbols; a manual imported-class virtual call
    links and returns 42.  Client objects do not duplicate imported
    vtables.

## Tests

Added `SepLib`/`SepProg` and `SepEmpty`/`SepEmptyProg`:
- library object contains no `main`;
- program object contains `main` and links against only the library
  object (not its `.mod`);
- exported data + library BEGIN works (`42`);
- bodyless library still exports init and links (`42`).

Manual M2make cross-object class check: `CLib.def/.mod` + `CProg.mod`
→ virtual `Area()` = 42.

## Limits

- `M2 -c` requires imported interfaces on the command line; `M2 -I`
  import scanning is deferred.  `M2make --separate` is the transitive
  resolver.
- `--separate` rebuilds all objects (no incremental build/ABI marker).
- Generics still need the generic body at the client; no separate
  generic-instance object emission yet.
- The fixpoint gate still compares the one-shot compiler image, not a
  multi-object self-host.

## Follow-up — `-I` and incremental objects (2026-10-24)

- `M2 -c -I dir` now recursively scans target/import source files,
  resolves `.def` files (including lower-case names), topologically
  orders them, and parses them before the target.
- `M2make --separate` now passes the target through `M2 -c -I ...`
  instead of an ever-growing explicit interface list.
- Stale-object checks use source/interface mtimes; a newer compiler
  binary is treated as an ABI event; shim changes relink.  A second run
  reports `up to date`.
- Added `SepResProg` (`M2 -c -I`), M2make separate up-to-date,
  single-object recompile and `.def`-change rebuild tests.
- Per-object self-hosting is now green.  The stage-2 compiler regression
  was caused by building compiler units without the legacy 1-D call ABI;
  `--m2flag -legacyopen1d` plus the new `bootstrap/fixpoint-separate.sh`
  builds stage2/stage3 as objects and compares all per-object `.ssa`
  (11 objects).

## Follow-up — ABI stamp and definition-only objects (2026-10-24)

- `M2make --separate` now records `gen_ssa/.m2abi` containing the ABI
  version and `--m2flag` settings; a missing/changed stamp rebuilds all
  objects.
- Modules with a `.def` but no `.mod` are compiled to
  `gen_ssa/<Module>.o`, so definition-only data and class vtables link.
- Added `CDefProg` (class-only `.def` vtable) and M2make checks for the
  ABI stamp and definition-only object.
- Suite is now 305/305.

## Generic-instance objects (2026-10-24)

- M2make detects `MODULE X = G(actuals)` in `.def`/`.mod` files and
  records `G` as a dependency.
- Abstract `GENERIC` modules are ordered but not compiled/linked.
- An instance module is compiled to its own `gen_ssa/<X>.o` with the
  generic template sources in the same session; the program links that
  object.
- Type, value, procedure and generic-class generics work through
  separate objects.  Imported instance implementations are parsed for
  method information but not lowered into the client object.
- Added M2make `GenProg` and coverage for qualified procedure actuals.

## Commits and tags

| commit | tag | work |
| --- | --- | --- |
| `0adc637` | `v3-separate-compilation` | stable symbols, `-c`, library/program split, init list, M2make `--separate`, tests/docs |
| `92d11d9` | `v3-separate-compilation-p1` | `M2 -I` transitive resolution, incremental M2make objects, tests/docs |
| this docs commit | `v3-separate-compilation-summary` | session summary |
| final docs commit | `v3-session-2026-10-24-separate-end` | session tag |

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