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w6c_ww: cgtypetest nullable is discriminates pointer-vs-null (#45 review)

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The #45 non-ident arm tag-compared the word in AX against the variant
index; for the nullable (*T | void) fold that word IS the pointer —
`h.m is *t` on a non-null pointer answered FALSE (silent cs≠ww,
cstage correct: CMPQ $0 + JE/JNE polarity per cgen.c N_TYPETEST).
The ident path had the same missing nullable arm since before #45
(pre-existing at master, unexercised in the bootstrap corpus). One
nullable branch at the shared compare choke-point closes both halves:
want stays RAW (cstage tests tag == ptr_tag unclamped, a no-match -1
takes the void polarity). Rows nullable_dot_field + nullable_ident
pin both polarities and both states in 927; whole-corpus control
(5 selfhost combined.ww, master-vs-branch w6c + w6c_ww) byte-id.
This commit is contained in:
Hojun-Cho
2026-06-04 04:54:43 +09:00
parent b2e4388792
commit b3d6bc4420
4 changed files with 108 additions and 17 deletions
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26
selfhost/cmd/wcc/cgenexpr.ww
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@@ -426,12 +426,14 @@ fn cgtypetest(c: *cgen, n: *node) void = {
};
};
let want: i32 = 0;
let nullcarrier: *node = scrutt;
if (nonident) {
// Variant index from the STAMPED scrutinee type (cstage:
// u = n->lhs->type) — matchscrutt's node-shape walk can't
// carry N_DOT (returns the scrut node, which the
// cgtagvariantidx N_TTAGGED gate rejects). flatvariantidx /
// flatslicevariantidx read .type_ off any stamped carrier.
nullcarrier = lhs;
if (n.rhs != nil) {
if (n.rhs.kind == nkind.N_TSLICE) {
want = flatslicevariantidx(c, lhs, n.rhs.lhs);
@@ -442,7 +444,6 @@ fn cgtypetest(c: *cgen, n: *node) void = {
} else {
want = cgtagvariantidx(c, scrutt, n.rhs);
};
if (want < 0) { want = 0; };
if (!nonident) {
emitline("\tMOVQ\t");
emitoff(scrutoff: i64);
@@ -450,10 +451,25 @@ fn cgtypetest(c: *cgen, n: *node) void = {
};
let nel: str = mklabel(c, "is_ne");
let dnl: str = mklabel(c, "is_done");
emitline("\tCMPQ\t$");
emitint(want: i64);
emitline(", AX\n");
emitline("\tJNE\t");
if (isnullabletype(nullcarrier)) {
// Nullable `(*T | void)` fold: the word in AX IS the
// pointer — discriminate pointer-vs-null, not tag-vs-index
// (cstage cgen.c N_TYPETEST nullable arm). `want` stays RAW
// here: cstage tests tag == ptr_tag unclamped, so a
// no-match (-1) takes the void polarity.
emitline("\tCMPQ\t$0, AX\n");
if (want == nullableptrtag(nullcarrier)) {
emitline("\tJE\t");
} else {
emitline("\tJNE\t");
};
} else {
if (want < 0) { want = 0; };
emitline("\tCMPQ\t$");
emitint(want: i64);
emitline(", AX\n");
emitline("\tJNE\t");
};
emitline(nel);
emitline("\n\tMOVQ\t$1, AX\n\tJMP\t");
emitline(dnl);