ww/test/lang/narrow_tail_widen_test.ww

// narrow_tail_widen_test — #14 commit-2: the narrow-tail aggregate-register
// materialise choke-point (cg_agg_reg_store / cgaggregstore), now reached by
// the WIDENED gates. Before #14 these sites gated `tail%8 ∈ {0,1,2,4}` and a
// 3/5/6/7-byte aggregate tail fell through to a lone narrow MOV (a SILENT
// both-stage member drop — both cstage and wwstage emitted IDENTICALLY wrong
// asm, so byte-id was GREEN and BLIND). Widening each gate to the full
// `sz<=24` routes 3/5/6/7 through the choke-point's non-padded scratch detour
// (dest_padded=false: MOVQ the tail eightbyte into a ceil-8 pad, then an
// exact `tail`-byte aggcopy into the packed dest).
//
// Each @test POISON-SEEDS every dest eightbyte with a sentinel distinct from
// every mk() value, performs the aggregate store, then value-asserts each
// eightbyte INCLUDING the dropped 3/5/6/7 tail word. A drop leaves the poison
// (mismatch). Where the dest is a PACKED field/element (C, D) a trailing
// neighbour is sentinel-checked too: it pins dest_padded=FALSE (a wrong =true
// would over-store the tail eightbyte and clobber the neighbour).
//
// Heterogeneous shapes per site + #111 (row-array @test blocked) => inline
// @test fns, not a row table. A 14B struct/array (maxalign<=2) keeps a real
// tail-6: an i64-bearing field pads to 16B (tail 0) and never trips it.

package narrow_tail_widen_test;

type t14 = struct { v: [7]i16 };               // 14B: full=1, tail=6
type boxed = struct { f: t14, guard: i16 };    // f@0 (14B), guard@14
type nested = struct { m: boxed };             // o.m.f chained dot
type myerr = !i32;                             // site B unwrap error variant

fn mk14() t14 = {
	return t14 { v = [10i16, 20i16, 30i16, 40i16, 50i16, 60i16, 70i16] };
};
fn mk7arr() [7]i16 = {
	return [10i16, 20i16, 30i16, 40i16, 50i16, 60i16, 70i16];
};
fn mk14res() (t14 | myerr) = {
	return t14 { v = [10i16, 20i16, 30i16, 40i16, 50i16, 60i16, 70i16] };
};

let gg: [7]i16 = [0i16, 0i16, 0i16, 0i16, 0i16, 0i16, 0i16];   // site G dest
let gb: boxed = boxed {                                        // site B dest
	f = t14 { v = [0i16, 0i16, 0i16, 0i16, 0i16, 0i16, 0i16] },
	guard = 0i16,
};

fn poison7(p: *[7]i16) void = {
	let i: i32 = 0;
	for (i < 7) { p[i] = 0x7f7fi16; i += 1; };
};

// Site F (cstage cgen.c N_ASSIGN local-ident array `g = call`; ww cgenexpr.ww
// 12574). Whole local array reassign from an aggregate-returning call.
@test fn f_local_array() void = {
	let g: [7]i16;
	poison7(&g);
	g = mk7arr();
	assert(g[0] == 10i16);
	assert(g[3] == 40i16);
	assert(g[4] == 50i16);   // eb1 byte 0-1
	assert(g[5] == 60i16);   // eb1 byte 2-3 — tail, dropped pre-#14
	assert(g[6] == 70i16);   // eb1 byte 4-5 — tail, dropped pre-#14
};

// Site F (struct twin; ww cgenexpr.ww 12537). Whole local struct reassign.
@test fn f_local_struct() void = {
	let s: t14;
	poison7(&s.v);
	s = mk14();
	assert(s.v[0] == 10i16);
	assert(s.v[4] == 50i16);
	assert(s.v[5] == 60i16);   // tail, dropped pre-#14
	assert(s.v[6] == 70i16);   // tail, dropped pre-#14
};

// Site G (cstage cgen.c N_ASSIGN global-ident array `g = call`, the inline
// loop now routed; ww cgenexpr.ww 12231). Whole GLOBAL array reassign — G
// had NO {0,1,2,4} gate, it dropped 3/5/6/7 via a lone MOVB.
@test fn g_global_array() void = {
	poison7(&gg);
	gg = mk7arr();
	assert(gg[0] == 10i16);
	assert(gg[4] == 50i16);
	assert(gg[5] == 60i16);   // tail, dropped pre-#14 (MOVB wrote only byte 0)
	assert(gg[6] == 70i16);   // tail, dropped pre-#14
};

// Site C (cstage cgen.c single-dot `b.f = call`; ww cgenexpr.ww 10845 local
// twin). PACKED field => guard neighbour pins dest_padded=false.
@test fn c_single_dot() void = {
	let b: boxed;
	poison7(&b.f.v);
	b.guard = 0x55aai16;          // neighbour sentinel
	b.f = mk14();
	assert(b.f.v[0] == 10i16);
	assert(b.f.v[4] == 50i16);
	assert(b.f.v[5] == 60i16);    // tail, dropped pre-#14
	assert(b.f.v[6] == 70i16);    // tail, dropped pre-#14
	assert(b.guard == 0x55aai16); // intact: tail aggcopy is exactly 6 bytes
};

// Site D (cstage cgen.c chained-dot terminal `o.m.f = call`; ww cgenexpr.ww
// 11781). PACKED field of a nested struct => guard neighbour check.
@test fn d_chained_dot() void = {
	let o: nested;
	poison7(&o.m.f.v);
	o.m.guard = 0x55aai16;
	o.m.f = mk14();
	assert(o.m.f.v[0] == 10i16);
	assert(o.m.f.v[4] == 50i16);
	assert(o.m.f.v[5] == 60i16);    // tail, dropped pre-#14
	assert(o.m.f.v[6] == 70i16);    // tail, dropped pre-#14
	assert(o.m.guard == 0x55aai16);
};

// Site A (cstage cgen.c cg_structlit_fill nested-CALL field; ww cgenutil.ww
// cgstructlitfill 5388). A struct-LITERAL whose field is an aggregate call.
@test fn a_structlit_field() void = {
	let x: boxed = boxed { f = mk14(), guard = 999i16 };
	assert(x.f.v[0] == 10i16);
	assert(x.f.v[4] == 50i16);
	assert(x.f.v[5] == 60i16);    // tail, dropped pre-#14
	assert(x.f.v[6] == 70i16);    // tail, dropped pre-#14
	assert(x.guard == 999i16);
};

// Site B (cstage cgen.c N_ASSIGN #16 global/chained `g.f = mk()!` unwrap; ww
// cgenexpr.ww 8483). A GLOBAL struct's field unwrap-receive — pre-#16 the
// generic single-word store DROPPED w1/w2; #16 routed it through the
// {AX,DX,CX} materialise, #14 widens its tail to 3/5/6/7.
@test fn b_global_unwrap() void = {
	poison7(&gb.f.v);
	gb.guard = 0x55aai16;
	gb.f = mk14res()!;
	assert(gb.f.v[0] == 10i16);
	assert(gb.f.v[4] == 50i16);
	assert(gb.f.v[5] == 60i16);    // tail, dropped pre-#14
	assert(gb.f.v[6] == 70i16);    // tail, dropped pre-#14
	assert(gb.guard == 0x55aai16);
};