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w6c: sret-wire the chained-leaf call store (o.a.b = wide())

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The chained value-struct walker's N_CALL arm handled only <=24B
register returns; an sret-class rhs fell to the scalar tail and
stored ONE word (the sret dest pointer) into the leaf -- silent
truncation in BOTH stages, byteid-blind. Point the callee's hidden
RDI at the BP-relative leaf slot (the single-dot #234 arm verbatim);
a ptr-root/global chain joins the #234-tail loud-stop family.
This commit is contained in:
Hojun-Cho
2026-08-08 23:51:17 +09:00
parent 62b9d20383
commit 94928470bc
4 changed files with 81 additions and 4 deletions
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23
cmd/w6c/cgen.c
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@@ -6768,6 +6768,29 @@ cgexpr(Cg *c, Node *n, Local *locals)
}
break;
}
/* #234: over-cap sret STORE into a chained
* value-struct leaf — `o.a.b = wide();`
* (cg_sret_retsize > 0: a >24B struct OR an
* over-cap tuple). Point the callee's hidden
* RDI dest at the leaf slot so it writes the
* WHOLE value there; pre-#234 this fell to
* the scalar tail and stored ONE word (the
* sret dest pointer). cg_sret_dest_off is
* BP-relative ONLY, so a ptr-root/global
* chain needs the runtime RDI-pointer dest
* variant deferred to #234-tail and HARD-
* STOPS loud (rule 7). */
if (n->rhs && n->rhs->kind == N_CALL
&& cg_sret_retsize(leaf_type) > 0) {
if (via_cx)
fatal("#234-tail: over-cap tuple "
"sret store to chained "
"ptr/global dest unsupported");
cg_sret_dest_off = base_disp + total_off;
cgexpr(c, n->rhs, locals);
cg_sret_dest_off = 0;
break;
}
/* TY_STRUCT terminal in the chained-DOT walker:
* three rhs shapes — mirror of the single-dot
* branch.