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wwstage: register error-structs in collectstructs so large-union struct-variant returns widen (#9)

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collectstructs registered a struct only when the typedecl body is N_TSTRUCT, so an error-struct (type X = !struct{...}, whose body is N_TBANG{N_TSTRUCT}) never entered wwstage's c.structs table. The name-keyed structlookup then missed at the return-widen sites, and wwstage dropped the struct construction when returning a struct variant of a large (>4-eightbyte) union -- wrong runtime value and cs!=ww. cstage has no struct name-table (pure tinfo) and was correct. Peel the N_TBANG body in collectstructs so error-structs register; both existing cstage-mirrored widen arms then fire. Provably byte-id-inert: no committed source defines a !struct today. Adds test/wcc/785 (struct-variant return + named-void control, both-stage byte-id + runtime). The >4-eightbyte 5th-word truncation on return remains, symmetric (cs==ww) and unread by the tag/early-word path; #222's sret hidden-pointer cutover is the committed fix (table-retirement tracked as the wwstage->tinfo SSoT arc). Aligns wwstage up to cstage (rule-10).
This commit is contained in:
Hojun-Cho
2026-05-30 04:54:12 +09:00
parent 7d39f6d623
commit 34c437fd63
6 changed files with 355 additions and 0 deletions
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25
selfhost/cmd/wwdump/main.combined.ww
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@@ -16349,6 +16349,20 @@ fn collectstructs(c: *cgen, file: *node) void = {
for (d != nil) {
if (d.kind == nkind.N_TYPEDECL) {
let body: *node = d.lhs;
// #9: an error-struct (`type X = !struct{...}`) carries an
// N_TBANG-wrapped body; peel it so X registers like any
// struct. cstage is tinfo-based and needs no table, but
// wwstage's name-keyed widen dispatch (cgreturn needswiden
// → cgwidentaggedstore) resolves struct layout through
// c.structs; an unregistered error-struct made the
// struct-variant-of-large-union return silently drop its
// construction (cs!=ww). The strategic fix is #222's sret
// cutover, which deletes this name-keyed dispatch outright;
// until then the table must be complete (errors.opaque_ is
// the first such type). #10 tracks retiring the table.
if (body != nil && body.kind == nkind.N_TBANG) {
body = body.lhs;
};
if (body != nil) {
if (body.kind == nkind.N_TSTRUCT) {
registerstruct(c, d.str, d.nmod, body);
@@ -25753,6 +25767,17 @@ fn cgreturn(c: *cgen, n: *node) void = {
};
cgwidentaggedstore(c, c.fnret.type_: *tinfo, rhs, "BP",
scroff, rsz);
// Tagged-return ABI loads at most 4 eightbytes
// (AX/DX/CX/R8). A union whose slot exceeds 32B
// (tag + >3 payload words, e.g. a 32B struct
// variant = 40B slot) drops its 5th+ word here —
// SYMMETRICALLY with cstage, so byte-id holds and
// the tag/early-word read paths are correct. The
// dropped tail is #222 (the >4-eightbyte sret ABI
// asymmetry); its real fix routes large unions
// through a hidden-pointer sret on both paths.
// Sound only while consumers never read the tail
// (errno's tag/strerror path does not).
emitline("\tMOVQ\t");
emitoff(scroff: i64);
emitline("(BP), AX\n");