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w6c: fall to the place resolver for indexed dot-chain aggregate sources

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The dot-chain SOURCE-address walkers (cg_dotchain_addr /
dotchainaddr) deliberately have no index hop — their AX-clean spill
contract serves the chained dotbase arm — so an aggregate copy from
elem[k].field (N_DOT over N_INDEX) fell out of the walk. Every
aggarg_srcaddr consumer loud-stopped (arg push #271, aggregate
return #272, field assign, structlit fill, ident reassign) EXCEPT
the indexed element-store arm, which left the walker's result
UNCHECKED and copied through a stale SI — a silent both-stage
miscompile (out[j] = hs[k].result read garbage). Task #6.

Both stages, two twin edits each: the aggarg_srcaddr N_DOT arm falls
back to cgplaceaddr (the C4/#40 place resolver, emission-free-on-
failure so the fallback starts clean), and the indexed store site
checks the walker before the same fallback.

Still loud (filed follow-ups): auto-deref pointer-to-array indexed
bases (hs: *[4]T; hs[k].field — cgplaceaddr's index arm takes no
deref hop; the explicit (*hs)[k].field form works), and the bare
N_INDEX slice-element aggregate source.
This commit is contained in:
Hojun-Cho
2026-08-08 17:12:18 +09:00
parent dc33af6217
commit d3822d7730
3 changed files with 184 additions and 15 deletions
Download Patch File Download Diff File Expand all files Collapse all files

33
selfhost/cmd/wcc/cgenexpr.ww
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@@ -1689,7 +1689,13 @@ fn aggargsrcaddr(c: *cgen, src: *syntax.node, dst: str) bool = {
return false;
};
if (src.kind == syntax.nkind.N_DOT) {
return dotchainaddr(c, src, dst);
if (dotchainaddr(c, src, dst)) { return true; };
// task #6: an N_INDEX link inside the dot chain
// (handles[k].result) — the chain walker has no index hop
// (AX-clean spill contract for dotbaseaddr); the place
// resolver is the C4/#40 fallback, and the failed walk is
// emission-free so the fallback starts clean.
return cgplaceaddr(c, src, dst);
};
if (src.kind == syntax.nkind.N_INDEX) {
let base: *syntax.node = src.lhs;
@@ -9778,15 +9784,26 @@ fn cgassign(c: *cgen, n: *syntax.node) void = {
emitsymname(c, n.rhs.str);
emitline("(SB), SI\n");
};
} else { if (n.rhs.kind == syntax.nkind.N_DOT) {
dotchainaddr(c, n.rhs, "SI");
} else {
if (!cgplaceaddr(c, n.rhs, "SI")) {
let msrc: str = "indexed aggregate assignment source unresolved\n";
os.write(2, msrc.ptr, msrc.len: u64);
os.exit(1);
// task #6: the chain walker
// declines an N_INDEX link
// (emission-free) — its result
// was unchecked here, so the
// copy below read through a
// stale SI. Fall to the
// generic place resolver.
let dok: bool = false;
if (n.rhs.kind == syntax.nkind.N_DOT) {
dok = dotchainaddr(c, n.rhs, "SI");
};
};};};
if (!dok) {
if (!cgplaceaddr(c, n.rhs, "SI")) {
let msrc: str = "indexed aggregate assignment source unresolved\n";
os.write(2, msrc.ptr, msrc.len: u64);
os.exit(1);
};
};
};};
emitline("\tPOPQ\tBX\n"); // dest
let kc: i32 = 0;
for (kc + 8 <= esz) {