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cgen: str a,s=call() N_MASSIGN tuple-elem store -> 3-word -- Phase 2 G3 (both stages)

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Reassign-destructuring a (scalar,str) tuple (a, s = call(), N_MASSIGN) stored only the str's ptr (DX->slot+0), dropping len/cap -- the last STORE-cluster gap. Reachable (valid ww; checker accepts str tuple elements) but unexercised in bootstrap (all N_MASSIGN sites returned <=8B tuples). Mirror the N_MLET destructure-store oracle (cgen.c:7475): on the one-str XOR, route the str's 3 words DX/CX/R8 -> slot+0/+8/+16; the slot pre-exists (localfind, not localadd). wwstage has no checker, so it derives str-ness from the callee return-type tuple via fnretlookupmod (structurally identical to cgmlet). Both XOR positions (str at l0 and l1). Kind-gated, never size==24. cstage==wwstage byte-identical.

Scope = one-str only, matching N_MLET exactly; str+str-both is unhandled by N_MLET too and is filed as a shared gap (task #22), with WHY-comments at both destructure sites. N_MLET emission unchanged (its edit is comment-only, verified byte-identical).

test/wcc/939: table-driven write-then-read-cap over both XOR positions (a,s=mk() and s,a=mk2()); cap!=len via mutation (not a sub-slice, #20); pre-poisoned via a non-G3 let-init; full triple+scalar asserted; fail-before/pass-after on both drivers. Completes the str-cap STORE cluster -- the read/write round-trip is now whole. main.combined.ww regenerated via the canonical make path.
This commit is contained in:
Hojun-Cho
2026-05-24 16:54:14 +09:00
parent b51a7daa25
commit 80527f3868
6 changed files with 559 additions and 8 deletions
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37
cmd/w6c/cgen.c
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@@ -7479,7 +7479,8 @@ cgstmt(Cg *c, Node *n, Local **locals, int *frame)
* Local sizing comes from each l->type so the str slot gets
* the full 24B; without this, only DX would land and the
* len/cap halves (CX/R8) would have nowhere to go.
* str IS []u8 (24B): the cap rides R8 (#1/Phase 3, task #5). */
* str IS []u8 (24B): the cap rides R8 (#1/Phase 3, task #5).
* one-str only; two-str destructure is gap (task #22). */
cgexpr(c, n->rhs, *locals);
Node *l0 = n->list;
Node *l1 = l0 ? l0->next : NULL;
@@ -7525,9 +7526,41 @@ cgstmt(Cg *c, Node *n, Local **locals, int *frame)
}
case N_MASSIGN: {
cgexpr(c, n->rhs, *locals);
ins1(c, A_PUSHQ, areg(D_DX));
Node *l0 = n->list;
Node *l1 = l0 ? l0->next : NULL;
/* one-str only; two-str destructure is gap (task #22). The str
* tuple element's 24B slot already exists (reassignment), so
* localfind it and mirror N_MLET's (DX,CX,R8)→(.ptr,.len,.cap)
* routing; the bare scalar fallback below would store only DX
* and drop len/cap. Scalar side stays AX→slot. */
Type *t0 = l0 ? l0->type : NULL;
Type *t1 = l1 ? l1->type : NULL;
Type *u0 = (t0 && t0->kind == TY_NAMED) ? t0->under : t0;
Type *u1 = (t1 && t1->kind == TY_NAMED) ? t1->under : t1;
int s0_is_str = u0 && u0->kind == TY_STR;
int s1_is_str = u1 && u1->kind == TY_STR;
if (l0 && l1 && l0->kind == N_IDENT && l1->kind == N_IDENT
&& (s0_is_str ^ s1_is_str)) {
int off0 = localfind(*locals, l0->str);
int off1 = localfind(*locals, l1->str);
if (off0 != 0 && off1 != 0) {
if (s0_is_str) {
/* l0 is str: ptr=DX, len=CX, cap=R8. l1 scalar = AX. */
ins2(c, A_MOVQ, areg(D_DX), amem(D_BP, off0 + 0));
ins2(c, A_MOVQ, areg(D_CX), amem(D_BP, off0 + 8));
ins2(c, A_MOVQ, areg(D_R8), amem(D_BP, off0 + 16));
ins2(c, A_MOVQ, areg(D_AX), amem(D_BP, off1));
} else {
/* l0 is scalar; l1 is str. */
ins2(c, A_MOVQ, areg(D_AX), amem(D_BP, off0));
ins2(c, A_MOVQ, areg(D_DX), amem(D_BP, off1 + 0));
ins2(c, A_MOVQ, areg(D_CX), amem(D_BP, off1 + 8));
ins2(c, A_MOVQ, areg(D_R8), amem(D_BP, off1 + 16));
}
break;
}
}
ins1(c, A_PUSHQ, areg(D_DX));
if (l0 && l0->kind == N_IDENT) {
int off = localfind(*locals, l0->str);
if (off != 0)