A `let c: T = *p` (T a struct or array, >8B) copied no full aggregate:
cstage dropped the init entirely (c read garbage); wwstage emitted only
the scalar `MOVQ AX,off(BP)` tail (first 8 bytes). Both wrong, differently
— converge BOTH stages on a size-driven slot-to-slot memcpy: cgexpr the
deref operand to the source address in AX, MOVQ AX,SI, then a MOVQ run
plus a sized MOVL/MOVW/MOVB tail over the #254 non-slot-padded ABI extent
(lu->size / structabisize for a struct, tinfo.size for an array). Mirror
arms in cgen.c N_LET and cgenstmt.ww cglet, byte-identical (rule-10).
Unblocks sha256's faithful `let copy = *h`. The by-value aggregate RETURN
ABI (array/struct return truncates to AX) is fold-2 (#267, deferred).
949 gains 6 full-readback rows (every member written distinct + summed,
so a truncated copy fails): struct{[4]u32} 16B, struct{[8]u32} 32B via
both *(&s) and *p (sha256 shape), bare [4]u32, and non-8-mult tails
([3]u32 12B → MOVL, [11]u8 11B → MOVW+MOVB). w6c+wwdump combined.ww regen
(#110). 61/61 949, test-unit 240, sizelint, smoke green.
Hojun-Cho
4d3f8467a8