ww/test/wcc/726_alias_leaf_collision.c

/*
 * 726_alias_leaf_collision — sentinel for #27. Pins wwstage's
 * aliaslookup to a same-module-first leaf walk so a bare `invalid`
 * inside module M (with `type invalid = !void;`) resolves to M's
 * underlying void, not to some other module's `type invalid = !i32;`
 * registered later in c.aliases.
 *
 * Pre-fix wwstage's `aliaslookup` (selfhost/cmd/wcc/cgen.ww) walked
 * c.aliases head-first by leaf name, returning the FIRST match. With
 * combined-source build orderings where a `type invalid = !i32;` from
 * lib/strconv sits ahead of utf8's `type invalid = !void;` in the
 * chain, `localloadop` resolved invalid → !i32 (size 4, signed) and
 * emitted MOVSXD on a slot the let-decl prologue zero-inited 8B-wide
 * (typeis8byteprimitive walks to void → MOVQ $0). Silent-correct-by-
 * zero-init: the upper 4B happened to be zero from the zero-init, so
 * the 4B sign-extend produced the right value, but the asm diverged
 * from cstage's MOVQ and 995_self_rebuild broke once any caller of
 * lib/strings/strings.byteindex (the (str|rune) match-arm shape that
 * dragged utf8 into the bootstrap closure) bumped the alias-chain
 * ordering.
 *
 * Cstage's `resolve_typename` (cmd/wcc/check.c:65) calls
 * `scope_lookup_prefer(cur, cur_mod, nm)` — same-module-first then
 * fallback. The fix mirrors that discipline in wwstage's aliaslookup.
 * Asserts byte-id between cstage and wwstage on a probe shape that
 * loses the asm divergence under the fix.
 */
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <sys/wait.h>

static int
runwait(const char *cmd)
{
	int rc = system(cmd);
	if (rc == -1) return -1;
	if (WIFEXITED(rc)) return WEXITSTATUS(rc);
	return -1;
}

struct row {
	const char *label;
	const char *src;
	/* `want` selects which assertion family runs on the emitted .s:
	 *   "movq_invalid" — post-zero-init load on beta.yield_more's
	 *                    invalid-slot must be MOVQ (the collision case).
	 *   "movsxd_i32"   — local i32 read in promote must be MOVSXD on
	 *                    BOTH stages. Guards future "fix" attempts
	 *                    that pessimize localloadop and would break
	 *                    legitimate signed-narrow loads. */
	const char *want;
};

/* Module ordering picked so the colliding `type invalid = !i32;` lands
 * later in c.aliases (head-prepend → at the head), masking module M's
 * own `type invalid = !void;`. `gamma` brings both modules into scope
 * via use directives so decl_mod tags both as imports — that gates
 * scope_define_in_module's per-mod dedup path on cstage's side. */
static const struct row rows[] = {
	{ "void_invalid_under_i32_collision",
	  "package gamma;\n"
	  "import alpha;\n"
	  "import beta;\n"
	  "export fn main() i32 = { return 0; };\n"
	  "package beta;\n"
	  "type more = void;\n"
	  "type invalid = !void;\n"
	  "fn yield_more() (rune | more | invalid) = {\n"
	  "    let e: invalid;\n"
	  "    return e;\n"
	  "};\n"
	  "package alpha;\n"
	  "export type invalid = !i32;\n",
	  "movq_invalid" },
	/* Regression guard: a real signed-narrow `let i: i32 = ...;` read
	 * MUST stay on MOVSXD. Any future "fix" that pessimizes
	 * localloadop to blanket-MOVQ in the name of #27 would silently
	 * regress this — losing sign-extension on i32 → i64 promotion
	 * (also drops the high half of a deref-store-narrowed slot). */
	{ "i32_local_read_keeps_movsxd",
	  "fn promote(x: i32) i64 = {\n"
	  "    let i: i32 = x;\n"
	  "    return (i: i64);\n"
	  "};\n",
	  "movsxd_i32" },
};

static int
emit_s(const char *w6c, const struct row *r, int i, char *out_s, size_t cap)
{
	char src[64], cmd[1024];
	snprintf(src, sizeof src, "/tmp/alc_%d_%d.ww", getpid(), i);
	snprintf(out_s, cap, "/tmp/alc_%d_%d_%s.s",
	    getpid(), i, w6c[strlen(w6c) - 1] == 'w' ? "ww" : "c");

	FILE *f = fopen(src, "wb");
	if (!f) return -1;
	fputs(r->src, f);
	fclose(f);

	snprintf(cmd, sizeof cmd, "%s -o %s %s 2>/dev/null", w6c, out_s, src);
	int rc = runwait(cmd);
	unlink(src);
	return rc;
}

static int
slurp(const char *path, char *buf, size_t cap)
{
	FILE *f = fopen(path, "rb");
	if (!f) return -1;
	size_t n = fread(buf, 1, cap - 1, f);
	fclose(f);
	buf[n] = '\0';
	return (int)n;
}

/* The yield_more body must read its tagged-return payload through an
 * 8B MOVQ. A MOVSXD on the same slot is the pre-fix silent-correct-
 * by-zero-init shape. */
static int
check_movq_after_zeroinit(const char *spath, const struct row *r,
    const char *stage)
{
	char buf[1 << 14];
	if (slurp(spath, buf, sizeof buf) < 0) {
		fprintf(stderr, "row[%s][%s]: cannot read %s\n",
		    r->label, stage, spath);
		return -1;
	}
	const char *fn = strstr(buf, "TEXT beta.yield_more");
	if (!fn) {
		fprintf(stderr, "row[%s][%s]: no TEXT beta.yield_more in %s\n",
		    r->label, stage, spath);
		return -1;
	}
	const char *zi = strstr(fn, "MOVQ\t$0, ");
	if (!zi) {
		fprintf(stderr, "row[%s][%s]: no zero-init store\n",
		    r->label, stage);
		return -1;
	}
	const char *bad = strstr(zi, "MOVSXD\t");
	const char *good = strstr(zi, "\n\tMOVQ\t-");
	const char *ret = strstr(zi, "RET");
	if (bad && (ret == NULL || bad < ret)) {
		fprintf(stderr,
		    "row[%s][%s]: post-zero-init slot read uses MOVSXD\n",
		    r->label, stage);
		return -1;
	}
	if (!good || (ret && good > ret)) {
		fprintf(stderr,
		    "row[%s][%s]: post-zero-init slot read missing MOVQ\n",
		    r->label, stage);
		return -1;
	}
	return 0;
}

/* Real i32 local read MUST stay MOVSXD. Any MOVQ load of `i` (the
 * narrow signed local) inside promote means a later "fix" pessimized
 * localloadop and silently dropped sign-extension. */
static int
check_movsxd_kept(const char *spath, const struct row *r, const char *stage)
{
	char buf[1 << 14];
	if (slurp(spath, buf, sizeof buf) < 0) {
		fprintf(stderr, "row[%s][%s]: cannot read %s\n",
		    r->label, stage, spath);
		return -1;
	}
	const char *fn = strstr(buf, "TEXT promote");
	if (!fn) {
		fprintf(stderr, "row[%s][%s]: no TEXT promote in %s\n",
		    r->label, stage, spath);
		return -1;
	}
	const char *ret = strstr(fn, "RET");
	const char *bp = fn;
	int sxd = 0;
	for (;;) {
		const char *p = strstr(bp, "MOVSXD\t-");
		if (!p || (ret && p > ret)) break;
		sxd++;
		bp = p + 1;
	}
	if (sxd < 2) {
		fprintf(stderr,
		    "row[%s][%s]: expected MOVSXD on i32 local reads, found %d\n",
		    r->label, stage, sxd);
		return -1;
	}
	return 0;
}

int
main(void)
{
	const char *bin = getenv("BIN");
	if (!bin) bin = "out/bin";
	char absbin[512];
	if (bin[0] != '/') {
		char cwd[256];
		if (getcwd(cwd, sizeof cwd) == NULL) return 1;
		snprintf(absbin, sizeof absbin, "%s/%s", cwd, bin);
		bin = absbin;
	}

	char w6c[640], w6c_ww[640];
	snprintf(w6c, sizeof w6c, "%s/w6c", bin);
	snprintf(w6c_ww, sizeof w6c_ww, "%s/w6c_ww", bin);

	int have_ww = (access(w6c_ww, X_OK) == 0);
	int n = (int)(sizeof rows / sizeof rows[0]);
	int total = 0, fail = 0;

	for (int i = 0; i < n; i++) {
		char cs_path[128], ws_path[128];

		if (emit_s(w6c, &rows[i], i, cs_path, sizeof cs_path) != 0) {
			fprintf(stderr,
			    "alias_leaf_collision[cstage][%s]: w6c failed\n",
			    rows[i].label);
			fail++; total++; continue;
		}
		total++;
		int rc;
		if (strcmp(rows[i].want, "movsxd_i32") == 0) {
			rc = check_movsxd_kept(cs_path, &rows[i], "cstage");
		} else {
			rc = check_movq_after_zeroinit(cs_path, &rows[i], "cstage");
		}
		if (rc != 0) fail++;

		if (!have_ww) { unlink(cs_path); continue; }

		if (emit_s(w6c_ww, &rows[i], i, ws_path, sizeof ws_path) != 0) {
			fprintf(stderr,
			    "alias_leaf_collision[wwstage][%s]: w6c_ww failed\n",
			    rows[i].label);
			fail++; total++;
			unlink(cs_path); continue;
		}
		total++;
		if (strcmp(rows[i].want, "movsxd_i32") == 0) {
			rc = check_movsxd_kept(ws_path, &rows[i], "wwstage");
		} else {
			rc = check_movq_after_zeroinit(ws_path, &rows[i], "wwstage");
		}
		if (rc != 0) fail++;

		/* byte-id between stages on the same input — the principled
		 * sentinel for the polarity catalog. */
		total++;
		char cmd[512];
		snprintf(cmd, sizeof cmd, "cmp -s %s %s", cs_path, ws_path);
		if (runwait(cmd) != 0) {
			fprintf(stderr,
			    "alias_leaf_collision[%s]: cstage vs wwstage asm differs\n",
			    rows[i].label);
			fail++;
		}

		unlink(cs_path); unlink(ws_path);
	}

	if (fail) {
		fprintf(stderr,
		    "alias_leaf_collision: %d/%d fixtures failed\n", fail, total);
		return 1;
	}
	printf("alias_leaf_collision: %d/%d ok\n", total, total);
	return 0;
}