C cgen has carried defer for a while (defers[] global + reverse
walk on every return). Selfhost cgen now mirrors:
- cgen struct: deferbuf (**node, LIFO stack) + defertop counter.
- cgstmt N_DEFER: push n.lhs.
- cgreturn: rundefers() at entry — same as the C cgen pattern.
- cgfn fall-through return: rundefers() before zero-AX+RET.
DEFER_MAX = 16 matches C cgen.
Two new e2e rows: defer with an explicit `return acc;` (321 mod 256
= 65), and defer firing on an implicit void-fn fall-through (87).
Both rows verified via the wwstage cgen too.
Defer's semantics: queued exprs fire LIFO before the return expr
is evaluated, so a return that reads memory mutated by a deferred
call sees the post-defer state. Matches C cgen and Hare.
ascii.digitval returns (i32 | void) instead of an i32 -1 sentinel.
Two callers updated to match-on the result (lib/ww/lex/lex.ww escape
parse, selfhost/test/smoke.ww probe 6).
`!` would have been more idiomatic at both call sites — both have
verified isxdigit beforehand — but the selfhost parser doesn't yet
recognize postfix `!`/`?`, so using them in bootstrap-bound code
breaks the 993/995 byte-identity gates. Match is fine for now.
Selfhost cgen follow-on for the 8-byte-rounded tagged-union ABI
(landed in 1e2f55a for the C side):
- cgenutil.slotsize: tagged size = 8 (tag) + max(payload), padded to
8-byte multiple. Was hardcoded 24.
- cgendecl prologue: spill size/8 arg registers, not always 3.
- cgenstmt cglet tagged-call path: spill the CX value-word only when
the slot is >16 bytes.
All three were emitting 3-register patterns appropriate to (T | str)
sized unions and overflowing the new 16-byte (i32 | void) slots.
