# V3 compiles itself (runtime) — stage-2 fixpoint for a test file

Tag `v3-selfcompiles`. Main suite 111/111.

## The milestone

The **self-compiled V3** (`/tmp/M2self`, built by V3 from its own
sources) now runs, parses, and emits code. For a test file its output
is **byte-identical** to the gm2-built V3's:

```
./M2      tests/t_constfold.mod  ->  gen_ssa/TConstFold.ssa
/tmp/M2self tests/t_constfold.mod -> gen_ssa/TConstFold.ssa
cmp: *** IDENTICAL ***
```

That is a stage-2 self-hosting fixpoint for `t_constfold`.

## Fixes in this step

1. **Eager `OR`/`AND` NIL dereferences** — gm2 short-circuits, V3 does
   not. Rewrote `SymTab`'s guard sites (`(x = NIL) OR (x^.…)`) into
   sequential checks, and the driver's `PrintListing` loop
   (`(nextErr # NIL) AND (nextErr^.line = …)`) into a `done` flag.
2. **Off-by-one in string scans** — `QbeGen`'s `Len`/`Cpy`/`App`/`ParseInt`
   looped with `i < HIGH(s)`; for a string *literal* `HIGH = len-1`, so
   the last character was dropped. `App(fname, "gen_ssa/")` produced
   `"gen_ssa"`, mangling the output file name. Changed to `<= HIGH(s)`.

## Status

- Self-compiled V3 compiles a small file correctly (byte-identical).
- Compiling the **whole compiler source set** with the self-compiled V3
  still aborts (rc 134) — the next runtime bug (likely a capacity or a
  construct in the compiler's own sources). This is the remaining path
  to the full 3-stage fixpoint.

## Remaining

1. Fix the self-image abort (diagnose with gdb on `/tmp/M2self` over the
   full set).
2. Cross-stage `FileIO` selection and `bootstrap/fixpoint.sh`
   (Stage1 gm2 → Stage2 V3 → Stage3 V3, byte-identical `.ssa`), with the
   stage-aware CR flag.

## Files

`compiler/src/{SymTab.mod,compiler.frm,QbeGen.mod,M2.lst}`.