M2compiler-V3/docs/summary_session-2026-10-24-separate-compilation.md

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 (3,806,078 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.

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

No push was performed.