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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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29
cmd/w6c/cgen.c
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@@ -11099,25 +11099,20 @@ cgexpr(Cg *c, Node *n, Local *locals)
areg(D_CX));
goto dot_done;
}
if (fu && fu->kind == TY_STR) {
ins2(c, A_MOVQ,
amem(base_reg,
base_disp + total_off + 0),
areg(D_AX));
ins2(c, A_MOVQ,
amem(base_reg,
base_disp + total_off + 8),
areg(D_BX));
goto dot_done;
}
if (fu && fu->kind == TY_SLICE) {
/* Slice leaf: load all three header
if (fu && (fu->kind == TY_STR
|| fu->kind == TY_SLICE)) {
/* str/slice leaf: load all three header
* words into (AX=ptr, BX=len, CX=cap)
* so the value follows the canonical
* slice-rhs convention. base_reg may
* be CX (global / `*T` root); load
* .cap LAST so the base survives the
* earlier reads. */
* slice-rhs convention. str IS []u8 —
* the same 24B {ptr,len,cap} header. #29:
* the str arm here used to load only
* ptr+len (cap dropped → a junk strlit
* before the chain left CX stale); merged
* so both load all three, both stages
* (#263). base_reg may be CX (global /
* `*T` root); load .cap LAST so the base
* survives the earlier reads. */
ins2(c, A_MOVQ,
amem(base_reg,
base_disp + total_off + 0),