A match whose scrutinee is a tagged field of a GLOBAL value-struct read
the tag/payload from the BP region (saved-BP + return-addr) instead of
g(SB) and returned garbage. Both stages were identical-wrong, so the
byte-id gate could not see it -- a gate-blind regression introduced by
M1 (#25): M1's in-place N_DOT match arm uses localfind(base), which
returns the 0 not-found sentinel for a global base, so 0+field.offset
landed in the frame.
Gate the in-place arm on a confirmed-local base -- `localfind(base)==0
&& let_islet/isletvar(base)`, verbatim from cstage's own global test at
cgen.c:2000 (both stages, same spelling). A global base now falls
through to the existing spill path, which cgexprs the scrutinee and
resolves g(SB). M1's local-field in-place ($32) path is untouched.
Regenerates the w6c and wwdump combined.ww. Table-driven 841 test
(global int/reassign/str-payload + a local-field M1 regression row),
runtime-discriminating: pre-fix returns garbage, post-fix 42 on both
stages; rob's direct-global-field spill caveat confirmed at runtime.
Hojun-Cho
c86c6a3bbf