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wcc: chained-dot str leaf loads the cap word, both stages

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A str field reached through a chained dot (o.i.s) emitted two loads
(ptr, len) and stored a stale CX as the cap — both stages, at any
non-zero chain depth. Emit the full header at the chained-dot leaf.
Review item #29.

Both stages move in one commit: one emission contract; splitting
would leave the byte-id gates red between the halves.
This commit is contained in:
Hojun-Cho
2026-06-12 21:07:55 +09:00
parent 0a6f500b8c
commit f00775759d
5 changed files with 75 additions and 119 deletions
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45
selfhost/cmd/wcc/cgenexpr.ww
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@@ -4351,40 +4351,17 @@ fn cgdot(c: *cgen, n: *node) void = {
};
return;
};
if (typeisstr(leaftype)) {
if (viacx) {
if (ptrroot) {
emitline("\tMOVQ\t");
emitoff(rootoff: i64);
emitline("(BP), CX\n");
} else {
emitline("\tLEAQ\t");
emitsymname(c, rootname);
emitline("(SB), CX\n");
};
emitline("\tMOVQ\t");
emitdispreg(totaloff: i64, "CX");
emitline(", AX\n");
emitline("\tMOVQ\t");
emitdispreg((totaloff + 8): i64, "CX");
emitline(", BX\n");
} else {
emitline("\tMOVQ\t");
emitoff((rootoff + totaloff): i64);
emitline("(BP), AX\n");
emitline("\tMOVQ\t");
emitoff((rootoff + totaloff + 8): i64);
emitline("(BP), BX\n");
};
return;
};
if (typeisslice(leaftype)) {
// Slice leaf: load all three header words into
// (AX=ptr, BX=len, CX=cap). For the viacx path
// (global or `*T` root) CX is the base; load
// .cap LAST so the base survives the earlier
// reads. For BP-rooted locals the registers
// don't alias so order is free.
if (typeisstr(leaftype) || typeisslice(leaftype)) {
// str/slice leaf: load all three header words into
// (AX=ptr, BX=len, CX=cap). str IS []u8 — the same 24B
// {ptr,len,cap} header. #29: the str leaf used to load
// only ptr+len here (cap dropped → a junk strlit before
// the chain left CX stale); merged into the slice arm so
// both load the full triple, both stages (#263). For the
// viacx path (global or `*T` root) CX is the base; load
// .cap LAST so the base survives the earlier reads. For
// BP-rooted locals the registers do not alias so order is
// free.
if (viacx) {
if (ptrroot) {
emitline("\tMOVQ\t");