Latent #21 has two surface shapes — register polarity in cgun
TK_AMP N_INDEX's complex-base arm, and indexbaseesz's
over-broad .ptr pseudo-field gate — that share a single semantic
path: &N_DOT[N_INDEX] where the inner N_DOT cannot be peeled
into a plain ident base. Polarity-A (cgenexpr.ww) lifted to
cstage's three-line shape; stride-B (cgenutil.ww) narrowed so
the .ptr arm only fires on actual str/slice inners and falls
through to the generic struct-field arm for struct N_TNAME
bases. The fixes compose at the same call site (esz from
indexbaseesz, then the IMULQ-or-elide gate, then complex-base
emit), so splitting them into two commits would leave a
half-fixed intermediate — neither half stands alone as a
bisect-clean closure. Sentinel 755_amp_dot_idx exercises both
shapes across 4 stride classes (slice-elem 24, struct-elem 16,
u8 stride-1 elide, i64 stride-8); pre-fix 5/12 fail, post-fix
12/12 ok. Latent silent miscompile in lib/memio + lib/bufio's
.ptr[i] shape also unmasked.
Hojun-Cho
d5e8d699d1