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cstage+selfhost+test: fix nested STRUCTLIT silent zero in BP-relative fills

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Pre-existing landmine surfaced by #5. For a struct literal whose
field value is itself an N_STRUCTLIT of a struct-typed field, the
inline field-walk did `cgexpr(field.lhs); store-AX-sized`. cgexpr
has no whole-struct-in-register convention, so the nested literal
landed AX = first qword and the trailing bytes silently stayed zero
(or stack garbage). Three BP-relative sites in each stage hit it:
N_LET, N_ASSIGN N_IDENT-lhs, and N_RETURN N_STRUCTLIT.

Fix: shared cg_structlit_fill_bp (cstage) / cgstructlitfillbp
(wwstage) helper handles TK_ELLIPSIS autofill, tagged-field
widening, float vs scalar store dispatch, AND recurses on
struct-typed N_STRUCTLIT field values at bp_off + field_off. All 3
sites in each stage now call the helper instead of the inline walk.

Scalar store dispatch is the explicit {1->MOVB, 4->MOVL, else MOVQ}
shape (not fieldstoreop, which would emit MOVW for fsz==2) to stay
byte-identical with cstage pending task #13. Sister N_ASSIGN N_DOT
structlit walks (via_ptr / global / BP-relative-through-N_DOT) keep
their inline walk and still drop nested-STRUCTLIT silently — tracked
as task #18.

703 covers 6 rows: let_nested_i64, let_nested_3deep, let_nested_i32,
let_nested_middle (i64; switch to i32 once #15 lands),
assign_ident_nested, return_nested. 995_self_rebuild byte-identity
preserved.
This commit is contained in:
Hojun-Cho
2026-05-15 18:14:33 +09:00
parent c4347499ee
commit 9d03e02881
8 changed files with 932 additions and 689 deletions
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73
selfhost/cmd/wcc/cgenexpr.ww
View File

@@ -5490,67 +5490,18 @@ fn cgassign(c: *cgen, n: *node) void = {
if (n.op == tkind.TK_ASSIGN) {
if (n.rhs != nil
&& n.rhs.kind == nkind.N_STRUCTLIT) {
let lcsz: i32 = lcnsz;
if (n.rhs.op == tkind.TK_ELLIPSIS) {
emitline("\tXORQ\tAX, AX\n");
let zi: i32 = 0;
for (zi + 8 <= lcsz) {
emitline("\tMOVQ\tAX, ");
emitoff((off + zi): i64);
emitline("(BP)\n");
zi += 8;
};
for (zi + 4 <= lcsz) {
emitline("\tMOVL\tAX, ");
emitoff((off + zi): i64);
emitline("(BP)\n");
zi += 4;
};
for (zi < lcsz) {
emitline("\tMOVB\tAX, ");
emitoff((off + zi): i64);
emitline("(BP)\n");
zi += 1;
};
};
let fldn: *node = n.rhs.list;
for (fldn != nil) {
if (fldn.kind == nkind.N_FIELD) {
let fnm: str = fldn.str;
let fi: *fieldinfo = lcsi.fields;
for (fi != nil) {
if (streq(fi.fname, fnm)) {
cgexpr(c, fldn.lhs);
if (isfloattype(c, fi.tnode)) {
let mov: str = "MOVSD";
if (isf32type(c, fi.tnode)) {
mov = "MOVSS";
};
emitline("\t");
emitline(mov);
emitline("\tX0, ");
emitoff((off + fi.foff): i64);
emitline("(BP)\n");
fi = nil;
} else {
let fsz: i32 = fi.fsz;
let op: str = "MOVQ";
if (fsz == 1) { op = "MOVB"; };
if (fsz == 4) { op = "MOVL"; };
emitline("\t");
emitline(op);
emitline("\tAX, ");
emitoff((off + fi.foff): i64);
emitline("(BP)\n");
fi = nil;
};
} else {
fi = fi.finext;
};
};
};
fldn = fldn.next;
};
// Delegate to the shared BP-relative
// structlit fill helper. Handles
// TK_ELLIPSIS autofill + per-field
// walk; nested struct-typed values
// recurse via the helper (#17 fix).
// Helper uses the explicit {1→MOVB,
// 4→MOVL, else MOVQ} sized-store
// dispatch (NOT fieldstoreop) to stay
// byte-identical with cstage pending
// #13 (fsz==2 MOVW divergence). See
// cgstructlitfillbp docstring.
cgstructlitfillbp(c, lcsi, n.rhs, off);
return;
};
if (n.rhs != nil