V3 self-hosting fixpoint reached

Tag v3-fixpoint. Main suite 111/111.

The milestone

V3, compiled by V3 itself, compiles the whole compiler source set to a byte-identical gen_ssa/M2.ssa:

M2   (built by gm2 -fiso)  compiles  SymTab QbeGen M2S M2P M2(driver)
                          ->  gen_ssa/M2.ssa         (1,991,439 bytes)
M2self (built by V3 from that image)  compiles the same set
                          ->  gen_ssa/M2.ssa
cmp: *** IDENTICAL (FULL FIXPOINT) ***

So Stage 2 (V3 compiling itself) reproduces Stage 1's image exactly — the self-hosting fixpoint.

The last fix

QbeGen.InitHeap, for a nested array (ARRAY … OF ARRAY …) on the heap/stack, allocated each element sub-array with NewHeap but never initialised its descriptor header. A local ARRAY [0..15] OF Name therefore had sub-descriptors with garbage headers, and passing names[i] to an ARRAY OF CHAR formal trapped in the scanner's GetName. Fix: call InitHeap(eb, elem) on each sub-array.

Repro:

TYPE Name = ARRAY [0..63] OF CHAR;
PROCEDURE P;
  VAR names: ARRAY [0..3] OF Name;  i: CARDINAL;
  PROCEDURE Set (VAR s: ARRAY OF CHAR); BEGIN s[0] := 'x' END Set;
BEGIN i := 0; Set(names[i]) END P;

How we got here (this arc)

From "sources compile and link" to the fixpoint, each step a real V3 runtime/ABI bug with a minimal repro: nested modules; inline record array fields; the NUL-terminated string model; p^ as a VAR actual; de-eagered NIL guards; off-by-one string scans; short-circuit AND/OR; and now nested-array heap initialisation.

Remaining (bootstrap polish)

bootstrap/fixpoint.sh: automate Stage1 gm2 → Stage2 V3 → Stage3 V3 and cmp the images (the manual chain above already shows Stage2 == Stage1). Stage-aware CR flag: -m for gm2, no -m for V3.
Cross-stage FileIO selection (stage 1 uses the host FileIO; stage 2+ the self-hosted runtime/syslib/FileIO).

Files

compiler/src/{QbeGen.mod,M2.lst}.

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