# Lower phase — L7 (the flip): status and plan (2026-10-05)

Branch **`ast-stage-c`**.  L7 = "flip: lower from the AST instead of
inline; delete the inline emit + `Fwd*` machinery".

## Why L7 is not incremental

The flip makes `Lower` the sole emitter.  The obstacle is that `QbeGen`
holds **one** session state, used by the inline emit *during* parse; a
per-unit `Lower` emit would be clobbered by the next unit's inline emit.
So the flip is a **big-bang**: either remove/suppress the grammar's 533
`QbeGen.*` call sites, or give `QbeGen` two states — neither is a
byte-verifiable step.

The pragmatic path is therefore a **session re-emit**: collect every
unit's AST and re-emit the whole session with `Lower` after parsing.
That is byte-comparable against the legacy session image and becomes the
flip once the inline emit is removed.

## Started (`d30abfd`, tag `v3-lower7-scaffold`)

- `Lower.LowerSession/LowerOneUnit/MaterializeGlobals`.
- Driver (`compiler.frm`) collects `GetUnit()` per file and calls
  `Lower.LowerSession` under `-lower`.
- `SymTab.Materialize` makes a unit's own VAR/CONST visible in
  `globScope`, so `GlobalRef` resolves `"<unit>_<name>"` at session end
  (the unit scopes are closed by then).
- Removed `Lower.Reset` from the `M2` root so the owned tables persist
  across a session.

Still scaffolding (inline emit untouched); suite **200/200**, FIXPOINT OK
(3,401,129 bytes).

## Gaps found (all fixable, all required for the flip)

1. **`DefUnit` builds no AST.**  Its `ConstBlock/TypeBlock/VarBlock/
   ProcHeading` loop never `AstAppend`s, so a definition module's AST has
   no decls; its proc *headings* (which consume backend temps) cannot be
   replayed.  Fix: append to `astDecl` in `DefUnit`.
2. **Owned-table size.**  `MaxProc=64` / `MaxSym=512` are sized for one
   unit; a full-session re-emit needs every module's procs/vars.  Growing
   them grows the compiler image (watch the 4 MiB `sessBuf`).
3. **Nested-module globals.**  `QualNode(outer, name)` does not see a
   nested scope's non-exported globals; `ReenterGlobals` re-enters them
   but with `curMod = -1` (empty `mod`), so `GlobalRef` falls back to
   `$name` instead of `$<outer>_<name>`.
4. **Definition-module proc replay** must emit only the heading
   (`BeginFunc`/`FuncParam`/`AbortFunc`), like `LowerMethodHeadings`.
5. Possibly more, revealed once a full session is compared.

## Plan

1. Fix (1) and (4); grow tables (2) within the image budget.
2. Compare `Lower.LowerSession`'s image against the legacy session image
   for the compiler's own sources (the real test).
3. Fix the remaining gaps until the session image byte-matches.
4. Flip: remove the inline emit; keep `Lower` per unit; the fixpoint
   becomes the gate.