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w6c: variant-tag miss is loud, never tag 0 (rule 7)

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Every variant-index lookup miss (-1) was silently clamped to tag 0
across both stages: tagged return (value + bare-void), widen store
(struct/slice/str/float/scalar arms + push fast path + field store),
widen tag-remap (identity scan + emit loop), match case compare,
is/as typetest, tryprop error remap, and the alloc-nomem propagation
(clamped to 1). All misses are checker-rejected upstream today, so
the clamps were dead -- but any future checker/cgen seam gap would
mis-tag silently (wrong arm, wrong error, false success). Rule 7:
each site now hard-stops with a per-construct diagnostic; nullable
arms keep their raw -1 by design (a miss encodes the void polarity
for `case null`). Corpus asm byte-unchanged; bootstrap fixed point
holds.
This commit is contained in:
Hojun-Cho
2026-08-09 00:12:21 +09:00
parent 94928470bc
commit 57d33acd1f
4 changed files with 140 additions and 34 deletions
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89
cmd/w6c/cgen.c
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@@ -2671,7 +2671,9 @@ cg_widen_tag_remap(Cg *c, Type *du, Type *su, int slot_off)
int identity = 1, idx = 0;
for (Tparam *p = su->params; p; p = p->next, idx++) {
int di = cg_tag_for_variant(du, p->type);
if (di < 0) di = 0;
if (di < 0)
fatal("tagged widen: source variant missing "
"from dst union (rule 7)");
if (di != idx) { identity = 0; break; }
}
if (identity) return;
@@ -2681,7 +2683,9 @@ cg_widen_tag_remap(Cg *c, Type *du, Type *su, int slot_off)
for (Tparam *p = su->params; p; p = p->next, idx++) {
const char *next = mklabel(c, "remap_next");
int di = cg_tag_for_variant(du, p->type);
if (di < 0) di = 0;
if (di < 0)
fatal("tagged widen: source variant missing "
"from dst union (rule 7)");
ins2(c, A_CMPQ, aimm(idx), areg(D_AX));
ins1(c, A_JNE, abranch(next));
ins2(c, A_MOVQ, aimm(di), areg(D_AX));
@@ -3079,7 +3083,7 @@ cg_widen_tagged_store(Cg *c, Local **locals_p, Type *dst, Node *src,
}
foff += wide ? 24 : 8;
}
ins2(c, A_MOVQ, aimm(tag < 0 ? 0 : tag),
ins2(c, A_MOVQ, aimm(tag),
amem(D_BP, write_off + 0));
if (via_outer) goto copy_out;
return;
@@ -3149,6 +3153,9 @@ cg_widen_tagged_store(Cg *c, Local **locals_p, Type *dst, Node *src,
ins2(c, A_MOVQ, areg(D_AX),
amem(D_BP, write_off + k));
int tag = cg_tag_for_variant(du, st);
if (tag < 0)
fatal("tagged widen: no variant tag for source "
"(rule 7)");
if (src->kind == N_IDENT) {
int soff = localfind(*locals_p, src->str);
int ssz = (int)su->size;
@@ -3198,7 +3205,7 @@ cg_widen_tagged_store(Cg *c, Local **locals_p, Type *dst, Node *src,
cg_structlit_fill(c, locals_p, su, src,
DST_BP, 0, NULL, write_off + 8);
}
ins2(c, A_MOVQ, aimm(tag < 0 ? 0 : tag),
ins2(c, A_MOVQ, aimm(tag),
amem(D_BP, write_off + 0));
if (via_outer) goto copy_out;
return;
@@ -3214,7 +3221,10 @@ cg_widen_tagged_store(Cg *c, Local **locals_p, Type *dst, Node *src,
ins2(c, A_MOVQ, areg(D_BX), amem(D_BP, write_off + 16));
ins2(c, A_MOVQ, areg(D_CX), amem(D_BP, write_off + 24));
int tag = cg_tag_for_variant(du, st);
ins2(c, A_MOVQ, aimm(tag < 0 ? 0 : tag),
if (tag < 0)
fatal("tagged widen: no variant tag for source "
"(rule 7)");
ins2(c, A_MOVQ, aimm(tag),
amem(D_BP, write_off + 0));
if (via_outer) goto copy_out;
return;
@@ -3246,7 +3256,10 @@ cg_widen_tagged_store(Cg *c, Local **locals_p, Type *dst, Node *src,
amem(D_BP, write_off + k));
}
int tag = cg_tag_for_variant(du, st);
ins2(c, A_MOVQ, aimm(tag < 0 ? 0 : tag),
if (tag < 0)
fatal("tagged widen: no variant tag for source "
"(rule 7)");
ins2(c, A_MOVQ, aimm(tag),
amem(D_BP, write_off + 0));
if (via_outer) goto copy_out;
return;
@@ -3266,7 +3279,10 @@ cg_widen_tagged_store(Cg *c, Local **locals_p, Type *dst, Node *src,
amem(D_BP, write_off + k));
}
int tag = cg_tag_for_variant(du, st);
ins2(c, A_MOVQ, aimm(tag < 0 ? 0 : tag), amem(D_BP, write_off + 0));
if (tag < 0)
fatal("tagged widen: no variant tag for source "
"(rule 7)");
ins2(c, A_MOVQ, aimm(tag), amem(D_BP, write_off + 0));
copy_out:
if (via_outer) {
/* cgexpr above clobbered base_reg — reload from spill, then
@@ -3318,7 +3334,9 @@ cg_widen_tagged_push(Cg *c, Local **locals_p, Type *dst, Node *src, int sz)
/* Direct-push fast path: str / slice / scalar / pointer. */
cgexpr(c, src, *locals_p);
int tag = cg_tag_for_variant(du, st);
if (tag < 0) tag = 0;
if (tag < 0)
fatal("tagged widen: no variant tag for source "
"(rule 7)");
if (type_isstr(st) || (su && su->kind == TY_STR)) {
/* str IS []u8: slot 32 [+0]=tag, [+8]=ptr, [+16]=len,
* [+24]=cap — same shape as the slice arm below. Push
@@ -5983,9 +6001,13 @@ cgexpr(Cg *c, Node *n, Local *locals)
areg(D_AX));
int v58tag =
cg_tag_for_variant(fu, st);
if (v58tag < 0)
fatal("tagged widen: "
"no variant tag "
"for source "
"(rule 7)");
ins2(c, A_MOVQ,
aimm(v58tag < 0
? 0 : v58tag),
aimm(v58tag),
amem(D_BX, foff + 0));
ins2(c, A_MOVQ,
areg(D_AX),
@@ -11165,23 +11187,32 @@ cgexpr(Cg *c, Node *n, Local *locals)
* if the tag matches any of the alts,
* jump to body; otherwise to the next
* case. */
if (tag < 0)
fatal("tagged match: case type "
"not in union (rule 7)");
char *body = mklabel(c, "match_body");
ins2(c, A_CMPQ, aimm(tag < 0 ? 0 : tag),
ins2(c, A_CMPQ, aimm(tag),
areg(D_AX));
ins1(c, A_JE, abranch(body));
for (Node *alt = cs->list; alt;
alt = alt->next) {
int atag = cg_tag_for_variant(
su, alt->type);
if (atag < 0)
fatal("tagged match: case type "
"not in union (rule 7)");
ins2(c, A_CMPQ,
aimm(atag < 0 ? 0 : atag),
aimm(atag),
areg(D_AX));
ins1(c, A_JE, abranch(body));
}
ins1(c, A_JMP, abranch(next));
label(c, body);
} else {
ins2(c, A_CMPQ, aimm(tag < 0 ? 0 : tag),
if (tag < 0)
fatal("tagged match: case type "
"not in union (rule 7)");
ins2(c, A_CMPQ, aimm(tag),
areg(D_AX));
ins1(c, A_JNE, abranch(next));
}
@@ -11348,7 +11379,9 @@ cgexpr(Cg *c, Node *n, Local *locals)
for (Tparam *p = u->params; p; p = p->next, i++) {
if (!cg_variant_is_error(u, i)) continue;
int j = cg_tag_for_variant(r, p->type);
if (j < 0) j = 0;
if (j < 0)
fatal("tryprop: error variant missing "
"from fn return union (rule 7)");
if (j == i) continue;
char *skip = mklabel(c, "tryprop_skip");
ins2(c, A_CMPQ, aimm(i), areg(D_AX));
@@ -11586,7 +11619,10 @@ cgexpr(Cg *c, Node *n, Local *locals)
ins1(c, A_JNE, abranch(ne));
} else {
int tag = cg_tag_for_variant(u, vt);
ins2(c, A_CMPQ, aimm(tag < 0 ? 0 : tag), areg(D_AX));
if (tag < 0)
fatal("tagged typetest: type not in union "
"(rule 7)");
ins2(c, A_CMPQ, aimm(tag), areg(D_AX));
ins1(c, A_JNE, abranch(ne));
}
ins2(c, A_MOVQ, aimm(1), areg(D_AX));
@@ -11709,8 +11745,11 @@ cgexpr(Cg *c, Node *n, Local *locals)
break;
}
int tag = cg_tag_for_variant(u, vt);
if (tag < 0)
fatal("tagged typetest: type not in union "
"(rule 7)");
ins2(c, A_MOVQ, amem(D_BP, sl_off + 0), areg(D_AX));
ins2(c, A_CMPQ, aimm(tag < 0 ? 0 : tag), areg(D_AX));
ins2(c, A_CMPQ, aimm(tag), areg(D_AX));
ins1(c, A_JE, abranch(ok));
ins2(c, A_MOVQ, aimm(1), areg(D_DI));
ins2(c, A_MOVQ, aimm(60), areg(D_AX));
@@ -13531,7 +13570,9 @@ cgstmt(Cg *c, Node *n, Local **locals, int *frame)
Type *r = cg_ret_type;
r = type_chase_named(r);
int nidx = cg_tag_for_variant(r, ty_nomem);
if (nidx < 0) nidx = 1;
if (nidx < 0)
fatal("tryprop: no nomem variant "
"in fn return union (rule 7)");
ins2(c, A_MOVQ, aimm(nidx), areg(D_AX));
ins2(c, A_MOVQ, areg(D_BP), areg(D_SP));
ins1(c, A_POPQ, areg(D_BP));
@@ -14130,7 +14171,9 @@ cgstmt(Cg *c, Node *n, Local **locals, int *frame)
* slot and the caller reads memory. */
if (cg_sret_retsize(rt) > 0) {
int tag = cg_tag_for_variant(rt, ty_void);
if (tag < 0) tag = 0;
if (tag < 0)
fatal("tagged return: no void "
"variant (rule 7)");
ins2(c, A_MOVQ,
amem(D_BP, cg_sret_arg_off),
areg(D_BX));
@@ -14150,7 +14193,9 @@ cgstmt(Cg *c, Node *n, Local **locals, int *frame)
ins2(c, A_MOVQ, aimm(0), areg(D_AX));
} else {
int tag = cg_tag_for_variant(rt, ty_void);
if (tag < 0) tag = 0;
if (tag < 0)
fatal("tagged return: no void "
"variant (rule 7)");
ins2(c, A_MOVQ, aimm(tag), areg(D_AX));
}
ins2(c, A_MOVQ, areg(D_BP), areg(D_SP));
@@ -14266,6 +14311,10 @@ cgstmt(Cg *c, Node *n, Local **locals, int *frame)
* caller (e.g. a slice-stride IMULQ) would
* land in slot+16 / slot+24. (Task #18.) */
int tag = cg_tag_for_variant(rt, vt);
if (tag < 0)
fatal("tagged return: no variant "
"tag for return value "
"(rule 7)");
int rsz = (int)rt->size;
cgexpr(c, n->lhs, *locals);
if (type_isslice(vt)) {
@@ -14332,7 +14381,7 @@ cgstmt(Cg *c, Node *n, Local **locals, int *frame)
ins2(c, A_MOVQ, aimm(0),
areg(D_R8));
}
ins2(c, A_MOVQ, aimm(tag < 0 ? 0 : tag),
ins2(c, A_MOVQ, aimm(tag),
areg(D_AX));
} else {
/* Struct variant or tagged-subset: