selfhost+test: decompose user-struct by-value params (#11)
wwstage param-slot allocator dispatched isfloat/istagged/isslice/
isstr/catch-all and skipped TY_STRUCT. `fn(a: S, b: S)` where S is
16B emitted $16 frame (DI/SI only); cstage emits $32 (DI/SI/DX/CX)
per SysV ABI.
Two-site fix mirroring cmd/w6c/cgen.c:6820 (callee prologue) and
:4240 (caller push):
- New structparamsize(c, t) helper in cgenutil.ww resolves the
TY_STRUCT TNAME chain, returns totsize for sizes (0,16], else 0.
>16B drops to stack — bug-compat with cstage's <=16 gate.
- New struct arm in cgfnparams + matching cgfn pre-scan in
cgendecl.ww. nw = (size>8) ? 2 : 1; partial-fit stitch (idx=5
+ nw=2) emits one reg + one stack tail.
- New struct branch in pushargsrev N_IDENT arm: MOVQ + PUSHQ
high→low so cgcall's existing pop drains correctly.
Test 717: 4 rows × {cstage, wwstage, asm-id}. Headline 2×16B,
mixed 16B+8B (caller-side surface), str+struct regression guard,
partial-fit 5×i64+16B stitch.
Hojun-Cho
69a817f0f3