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cgen: c2 variant pass-2 structural fallback chases the full NAMED chain — both stages fused

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F2a batch-4 c2. Site: cgenutil.ww flatvariantidxt pass-2 (was :2895
at 74195ac, :2903 at 4adf914 post-batch-3) + cs twin cg_tag_for_variant
(cmd/w6c/cgen.c:920-933).

The structural fallback matched a bare source against a NAMED variant
by peeling exactly ONE level (pu.under compare) — a 2-level-alias
variant (type a=*X; type b=a) missed every pass and the widen
defaulted to tag 0, SILENT (the legacy-#17-comment class; that
comment's "task #17" label is retired here — current task #17 is the
unrelated arrlit item).

cs-twin probe DECIDED THE FUSE (spec obligation): v2_alias2 (bare
*i64 into 2-level ptr-alias variant) ran exit 1/1 BOTH-WRONG-IDENTICAL
byte-id pre-fix — cs has the identical single peel, so both stages fix
in this commit (NOT ww-only align-up). NOTE: the cs BINARY is NOT
frozen this train — this commit legitimately moves cstage codegen;
movers must stay bounded to the c2 family (verdict-sweep obligation).
Fix: typeeq/type_eq against tichase/type_chase_named of the variant;
the TY_NAMED gate keeps bare variants in pass-1's exact domain; drew's
>=2-candidate hard-error now guards the CHASED match set (v2_ambig
pins it HOLDING; v2_ambig2 pins the RATIFIED acceptance NARROWING —
2-level twins flip build-accepted-silent-mis-tag -> hard-error BOTH
stages, FLAG-P1/kb4_v2_ambig2). Not nominal-sensitive beyond the
documented proviso — the chase only deepens the structural compare;
nominal choice among >=2 candidates still hard-errors (#209/#211 hold
condition does not trip).

ROUTE-TRACE (rob's §3 ruling) — outcome (b): post-c2 the c4_bool2
shape (2-level bool alias variant, concrete-bool source on ww) runs
0/0 fully BYTE-ID — ww's concrete bool (the #90 stamp divergence,
still open) now reaches the variant through the chased structural
fallback and converges with cs's untyped-funnel route on the same
tag. The graduation therefore belongs to THIS commit: 944
untyped_bool2lvl_bound90 flips K_RUN_CS -> K_RUN here; c5 (#90 stamp
flip) pins its own acceptance rows.

Pin rows (944, all OBSERVED at the c1 base):
  v2_ctrl    bare *T into 1-level NAMED-*T (io vtable shape)
             pre 0/0 byte-id -> post HOLDS (the #15 consumer);
  v2_alias2  bare *T into 2-level alias variant
             pre cs1/ww1 byte-id (both-wrong) -> post 0/0 byte-id;
  v2_struct2 bare anonymous-let struct into 2-level alias variant
             pre cs1/ww1 -> post 0/0 runtime; byte-id SKIPPED via new
             K_RUN_NOID row kind: asm diverges on 3 PRE-EXISTING cglet
             zero-fill lines (cs XORQ+2 stores, ww none — #81 class,
             runtime-correct both, orthogonal to the tag; observed
             identical pre/post). Flip to K_RUN when that closes. The
             adjacent NAMED-source shape is task #95 (ken b4-oracle),
             OUT of this set;
  v2_ambig   bare source matching >=2 NAMED variants (1-level twins)
             -> hard-error HOLDS both stages (K_BUILDERR, diag pinned);
  v2_ambig2  2-LEVEL twin variants — the RATIFIED narrowing pin:
             pre build-ACCEPTED both stages (chase-less fallback
             matched neither twin; silent mis-tag, byte-identical)
             -> post HARD-ERROR both stages (K_BUILDERR, diag pinned).

Corpus: five-mains NEUTRAL vs the c1 build on identical inputs (both
stages — the 2-level variant shape is zero-in-corpus, as the old
comment predicted); cs==ww byte-id holds; 944 181/181.
combined.ww regens ride along.
This commit is contained in:
Hojun-Cho
2026-06-06 00:08:04 +09:00
parent b26b3dbdc5
commit 4e174099bd
5 changed files with 125 additions and 30 deletions
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15
selfhost/cmd/wwdump/main.combined.ww
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@@ -18973,13 +18973,18 @@ fn flatvariantidxt(tagged: *tinfo, want: *tinfo) i32 = {
let found: i32 = -1;
let n: i32 = 0;
for (q != nil) {
// One-level NAMED unwrap: a chained ptr-alias variant
// (type a=*X; type b=a) isn't reached here, so it would
// silently mis-tag — unexercised (zero in corpus), see
// task #17.
// Full chase (F2a batch-4 c2): the old one-level
// unwrap missed a chained ptr-alias variant
// (type a=*X; type b=a) — every pass fell through
// and the widen defaulted to tag 0, SILENT. The
// TY_NAMED gate keeps bare variants in pass-1's
// exact domain; drew's >=2-candidate hard-error
// below now guards the CHASED match set. cs twin
// cg_tag_for_variant fused in this commit (probe:
// both-wrong-identical pre-fix).
let pu: *tinfo = q.type_;
if (pu != nil && pu.kind == tykind.TY_NAMED
&& pu.under != nil && typeeq(pu.under, want)) {
&& typeeq(tichase(pu), want)) {
if (found < 0) { found = qi; };
n += 1;
};