# Session summary — 2026-10-04 (b): Lower phase L0–L2, L3 finding

Branch **`ast-stage-c`**.  Suite **182/182**; self-hosting fixpoint **OK**
(**3,147,849 bytes**).

The Lower phase (`docs/plan-lower.md`) went from a design to a working
byte-compare harness plus three verified subsets — and hit a real
architectural wall at L3 that is now precisely documented.

## Landed

| Tag | Doc | What |
| --- | --- | --- |
| `v3-lower0` | `summary_two-phase-lower0.md` | mechanism: `Lower` module, `QbeGen.SetOutName`, `-lower` flag, `lower_ok` compare; scalar L0 |
| `v3-lower1` | `summary_two-phase-lower1.md` | relations, booleans, short-circuit `AND`/`OR`, `NOT` |
| `v3-lower2` | `summary_two-phase-lower2.md` | `IF`/`ELSIF`/`ELSE`, `WHILE`, `REPEAT`, `LOOP`/`EXIT`, `FOR` (no `BY`), `HALT` |
| `v3-lower3-wip` | `summary_two-phase-lower3-finding.md` | L3 groundwork (calls, proc headers, `ParamName`, local capture, callee fix) + the blocking finding |

## How the comparison works

`-lower` makes the grammar re-emit the program unit from the AST after the
legacy `EndModule` and before `SymTab.EndUnit`; `LowerUnit` writes
`gen_ssa/<Mod>L.ssa` and `lower_ok` byte-compares it to the legacy image.
Four tests pass: `t_exit`, `t_arith`, `t_lower1`, `t_lower2`.

## The L3 finding

`SymTab.CloseProc`/`EndUnit` close the scope the inline actions lowered
inside.  `Lower` at unit end can resolve module names but **not procedure
locals/params**, so L3 does not byte-compare.  Fixing it at each
procedure ("option 1") needs the `L` image built **concurrently** with the
legacy one — but `QbeGen` has one buffer and one counter set, so
interleaved emitters corrupt the legacy path.  A second buffer was tried
and reverted; it does not address the shared counters.

**Conclusion:** the right step is the **flip** (L7) applied to the test
path — under `-lower`, suppress the legacy emit and lower the whole unit
from the AST *during* the parse, when every scope is open.  That
completes L3 and subsumes the rest.

## Bugs found & fixed (L3 groundwork)

- `NkCall` child 0 is an `NkDesignator`, not a bare `NkIdent`; calls were
  mangling as `$_0`.  Fixed with `CalleeName`.
- Procedure `VAR` locals were never recorded (`Block` set `astStmt`, not
  the decls); now captured via `astBlkDecls` → `NkProcDecl` child 2.
- `FORWARD` declarations break gm2's whole-program pass (find: L2) — the
  walk merges mutually-recursive bodies instead.

## State / next

- Tags `v3-lower0..2`, `v3-lower3-wip`.  Only `compiler/toto.mod` dirty.
- **Next:** start the flip (emit gate + AST lowering during parse),
  completing L3 and giving the basis for L4+.

## Resume

```sh
cd ~/Projets/Projets-Modula2/MyWork/m2compiler-V3
git checkout ast-stage-c
cd compiler && ./build.sh && ./run_tests.sh   # 182/182
cd .. && ./bootstrap/fixpoint.sh              # FIXPOINT OK
```