A.2's slotsize fast-path covered PTR/SLICE/CHAN/FN/STR but bailed on
TAGGED (no nullable fold) and on primitives (cstage let_emit_size pads
to 8B for slot storage; tinfo.size is natural width). Fallback hit
count under wwdump build was 2187. A.3 closes both gaps.
tinfo gains a `nullable: i32` field (fits the existing 4B pad, struct
stays 96B). tinfofornode's N_TTAGGED arm detects `(*T | void)` (exactly
2 variants, one N_TPTR, one bare N_TNAME "void" — aliased or !void-
wrapped void don't match) and folds to size=8, align=8, nullable=1.
Mirrors cmd/wcc/check.c:412-426.
slotsize fast-path re-adds TY_TAGGED (safe now) and gains a primitive-
pad branch: BOOL/RUNE/I8-I64/U8-U64/INT/UINT/UINTPTR/ENUM/F32/F64 →
return 8. Padding lives at the read site; tinfo.size remains a faithful
natural-width SSoT. TUPLE/TSTRUCT/TARRAY deliberately stay on the
fallback because per-field stride is registerstruct.totsize, not
tinfo.size.
Post-A.3 fallback hit count: 134 (94% reduction from A.2's 2187).
Reviewer's per-kind breakdown: N_TNAME 101 (alias-to-struct chains)
+ N_TARRAY 33 (struct-element rounding) account for all remaining
hits. Both A.4 work.
Probes: `(*i32 | void)` byte-identical between stages with the
8B nullable encoding. `(*i32 | nomem)` correctly does NOT fold
(nomem ≠ bare void). `(*i32 | !void)` correctly does NOT fold
(N_TBANG isn't N_TNAME).
131/131 + 994 + 995 + bootstrap byte-identical (ww2==ww3==ww4).
Hojun-Cho
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