# V3 step 1.9 — statements + boolean/relational core (done 2026-09-19)

Interactive grammar §4 (last big section before composites).
Suite 28/28 (13 run + 15 reject), LL(1)-clean throughout.

## Grammar (`compiler/src/M2.atg`)

- `Expr = SimExpr [Rel SimExpr]`: `= # < <= > >=` (no `<>`, no `IN`
  yet), `RelCheck` → 213, result BOOLEAN via new `QbeGen.Cmp`
  (ceqw/cnew/csltw/cslew/csgtw/csgew, eager 0/1).
- `OR`/`AND` (BoolCheck → 212) eager via or/and; `NOT` via xor-1.
- `BOOLEAN`/`CHAR` variables load like integers now (still `w`);
  named CHAR consts load too; other named-const use stays 230.
  `VAR x: BOOLEAN/CHAR` accepted (enums/subranges still 230).
- Statements: IF/ELSIF/ELSE, WHILE, REPEAT/UNTIL, LOOP/EXIT
  (230 outside LOOP via loop-label stack), FOR/TO/static-sign-BY,
  full CASE (labels, `a..b` ranges, ELSE), RETURN with 232 checks
  (outside proc / value-vs-proper mismatch / missing value).
- FOR: integer var + integer bounds (220), literal non-zero BY
  (ConstInt; non-literal → 230, zero → 220), sign picks cslew/csgew.
- WITH waits for records (step 3).

## Backend (`QbeGen`: labels, jumps, dead positions)

New: deterministic `@LN` labels, EmitLabel/Jmp/Jnz, Cmp, NotQ,
LOOP-exit stack. Plus the section's hard lesson, handled once in
the backend instead of every action:

- QBE forbids instructions after a terminator with no intervening
  label. Two rules fix all shapes: (1) value-emitters auto-open an
  unreachable block past a terminator (keeps every temporary
  defined — a *skipped* definition would dangle later uses);
  (2) Jmp/Jnz past a terminator are skipped (provably unreachable).
- CASE needed a real layout fix on top: each alternative now ends
  its tests with `jmp lAfter`, so no-match fallthrough skips the
  body (`cmp; jnz(lBody,lF); lF: ...; jmp lAfter; lBody: S; ...
  lAfter:`). The first attempt (fallthrough into the body) ran the
  wrong branch and is recorded here so it isn't reinvented.

## SymTab (small)

Proc-stack: EnterProc/ReenterProc push, new CloseProc pops both
scope and stack (all three heading sites converted); InProc/CurRes
drive the RETURN 232s. Frame gains 232 "bad RETURN".

## Bugs the tests caught

1. Missing LOOP back-edge — the exact bug Test2's own summary
   records ("body ran once"); t_loop proved it again.
2. CASE no-match fallthrough executed the first body (100 vs 103).
3. Double-terminator QBE rejections (EXIT inside IF bodies).

## Tests

Run: t_if/while/repeat/loop/for (incl. `BY -2` and empty-range
skip)/case (labels+ranges+ELSE)/bool (vars, chars, `#`, NOT) +
`showcase3` tour → 183. Reject: 214 non-boolean WHILE, stray EXIT,
module-level `RETURN 1`, `BY 0`. Total 28 (13 run + 15 reject).

Open (step 2/3/4): REAL lowering, `WITH`, `IN`, CHAR arithmetic
policy (currently 211), unmatched-FORWARD 231, call emission.