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w6c+wwstage: full-size aggregate copy for deref-rhs let-init (#265 fold-1)

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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.
This commit is contained in:
Hojun-Cho
2026-06-02 09:31:44 +09:00
parent 0afe4225cd
commit 4d3f8467a8
5 changed files with 331 additions and 0 deletions
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43
cmd/w6c/cgen.c
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@@ -8763,6 +8763,49 @@ cgstmt(Cg *c, Node *n, Local **locals, int *frame)
break;
}
}
/* #265 fold-1: aggregate deref-rhs let-init
* `let c: T = *p` (T a struct or array, >8B). Neither
* the scalar tail below (one 8B word) nor a missing arm
* (cstage dropped the copy entirely) materialised the
* whole aggregate. cgexpr(rhs->lhs) leaves the SOURCE
* ADDRESS in AX (a `*p` ident loads the pointer value;
* `*(&s)` LEAQs the slot); memcpy sz bytes slot→slot via
* SI — a MOVQ run plus a sized MOVL/MOVW/MOVB tail. N is
* lu->size (sz), the #254 non-slot-padded ABI extent. Both
* stages emit this identical sequence (rule-10); the by-
* value RETURN ABI is fold-2 (#267). */
if (n->rhs && n->rhs->kind == N_UN
&& n->rhs->op == TK_STAR && lu
&& (lu->kind == TY_STRUCT || lu->kind == TY_ARRAY)
&& sz > 8) {
cgexpr(c, n->rhs->lhs, *locals);
ins2(c, A_MOVQ, areg(D_AX), areg(D_SI));
int k = 0;
for (; k + 8 <= sz; k += 8) {
ins2(c, A_MOVQ, amem(D_SI, k), areg(D_AX));
ins2(c, A_MOVQ, areg(D_AX),
amem(D_BP, off + k));
}
if (k + 4 <= sz) {
ins2(c, A_MOVL, amem(D_SI, k), areg(D_AX));
ins2(c, A_MOVL, areg(D_AX),
amem(D_BP, off + k));
k += 4;
}
if (k + 2 <= sz) {
ins2(c, A_MOVW, amem(D_SI, k), areg(D_AX));
ins2(c, A_MOVW, areg(D_AX),
amem(D_BP, off + k));
k += 2;
}
if (k + 1 <= sz) {
ins2(c, A_MOVB, amem(D_SI, k), areg(D_AX));
ins2(c, A_MOVB, areg(D_AX),
amem(D_BP, off + k));
k += 1;
}
break;
}
if (n->rhs && sz == 8) {
cgexpr(c, n->rhs, *locals);
if (isf) {