broken_source:
"""Failure Map reference implementation. Python standard library only."""
import json

N = 1
observations = []
def solve(code):
    effects = {'push': (0, 1), 'pop': (1, -1), 'dup': (1, 1), 'dup_x1': (2, 1), 'swap': (2, 0),
               'add': (2, -1), 'ifeq': (1, -1), 'goto': (0, 0), 'return': (1, -1)}
    def verify():
        depth = {0: 0}
        work = [0]
        maxd = 0
        while work:
            i = work.pop()
            op, arg = code[i]
            need, delta = effects[op]
            d = depth[i]
            if d < need:
                return ['underflow', i]
            nd = d + delta
            maxd = max(maxd, nd)
            if op == 'goto':
                succ = [i + 1, arg]
            elif op == 'ifeq':
                succ = [i + 1, arg]
            elif op == 'return':
                succ = []
            else:
                succ = [i + 1]
            for s in succ:
                if s < 0 or s >= len(code):
                    return ['falls-off', i]
                if s in depth:
                    if depth[s] != nd:
                        return ['inconsistent', s]
                else:
                    depth[s] = nd
                    work.append(s)
        return ['ok', maxd]
    try:
        return verify()
    except (IndexError, KeyError):
        return ['vm-crash']
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
cases = [[('dup_x1 with one item underflows', ([['push', 1], ['dup_x1', None], ['return', None]],), ['underflow', 1]),
  ('dup_x1 with two items is legal',
   ([['push', 1], ['push', 2], ['dup_x1', None], ['add', None], ['add', None], ['return', None]],),
   ['ok', 3]),
  ('regression: dead code after goto is not verified',
   ([['push', 1], ['goto', 3], ['add', None], ['return', None]],),
   ['ok', 1]),
  ('if/else arms merge at equal depth',
   ([['push', 0], ['ifeq', 4], ['push', 5], ['goto', 5], ['push', 7], ['return', None]],),
   ['ok', 1]),
  ('ifeq on empty stack underflows', ([['ifeq', 1], ['push', 1], ['return', None]],), ['underflow', 0]),
  ('deeper arm reaching merge first is inconsistent',
   ([['push', 1], ['push', 0], ['ifeq', 4], ['pop', None], ['return', None]],),
   ['inconsistent', 4]),
  ('shallower arm reaching merge first is inconsistent',
   ([['push', 1], ['ifeq', 3], ['push', 9], ['push', 1], ['return', None]],),
   ['inconsistent', 3]),
  ('execution falling off the end', ([['push', 1], ['push', 1]],), ['falls-off', 1]),
  ('negative branch target', ([['push', 1], ['goto', -1], ['return', None]],), ['falls-off', 1]),
  ('swap with one item underflows', ([['push', 1], ['swap', None], ['return', None]],), ['underflow', 1])],
 [('dup_x1 with one item underflows',
   ([['push', 1], ['pop', None], ['push', 1], ['dup_x1', None], ['return', None]],),
   ['underflow', 3]),
  ('dup_x1 with two items is legal',
   ([['push', 1],
     ['pop', None],
     ['push', 1],
     ['push', 2],
     ['dup_x1', None],
     ['add', None],
     ['add', None],
     ['return', None]],),
   ['ok', 3]),
  ('regression: dead code after goto is not verified',
   ([['push', 1], ['pop', None], ['push', 1], ['goto', 5], ['add', None], ['return', None]],),
   ['ok', 1]),
  ('if/else arms merge at equal depth',
   ([['push', 1],
     ['pop', None],
     ['push', 0],
     ['ifeq', 6],
     ['push', 5],
     ['goto', 7],
     ['push', 7],
     ['return', None]],),
   ['ok', 1]),
  ('ifeq on empty stack underflows',
   ([['push', 1], ['pop', None], ['ifeq', 3], ['push', 1], ['return', None]],),
   ['underflow', 2]),
  ('deeper arm reaching merge first is inconsistent',
   ([['push', 1], ['pop', None], ['push', 1], ['push', 0], ['ifeq', 6], ['pop', None], ['return', None]],),
   ['inconsistent', 6]),
  ('shallower arm reaching merge first is inconsistent',
   ([['push', 1], ['pop', None], ['push', 1], ['ifeq', 5], ['push', 9], ['push', 1], ['return', None]],),
   ['inconsistent', 5]),
  ('execution falling off the end', ([['push', 1], ['pop', None], ['push', 1]],), ['falls-off', 2]),
  ('negative branch target',
   ([['push', 1], ['pop', None], ['push', 1], ['goto', -1], ['return', None]],),
   ['falls-off', 3]),
  ('swap with one item underflows',
   ([['push', 1], ['pop', None], ['push', 1], ['swap', None], ['return', None]],),
   ['underflow', 3])],
 [('dup_x1 with one item underflows',
   ([['push', 1],
     ['pop', None],
     ['push', 2],
     ['pop', None],
     ['push', 1],
     ['dup_x1', None],
     ['return', None]],),
   ['underflow', 5]),
  ('dup_x1 with two items is legal',
   ([['push', 1],
     ['pop', None],
     ['push', 2],
     ['pop', None],
     ['push', 1],
     ['push', 2],
     ['dup_x1', None],
     ['add', None],
     ['add', None],
     ['return', None]],),
   ['ok', 3]),
  ('regression: dead code after goto is not verified',
   ([['push', 1],
     ['pop', None],
     ['push', 2],
     ['pop', None],
     ['push', 1],
     ['goto', 7],
     ['add', None],
     ['return', None]],),
   ['ok', 1]),
  ('if/else arms merge at equal depth',
   ([['push', 1],
     ['pop', None],
     ['push', 2],
     ['pop', None],
     ['push', 0],
     ['ifeq', 8],
     ['push', 5],
     ['goto', 9],
     ['push', 7],
     ['return', None]],),
   ['ok', 1]),
  ('ifeq on empty stack underflows',
   ([['push', 1], ['pop', None], ['push', 2], ['pop', None], ['ifeq', 5], ['push', 1], ['return', None]],),
   ['underflow', 4]),
  ('deeper arm reaching merge first is inconsistent',
   ([['push', 1],
     ['pop', None],
     ['push', 2],
     ['pop', None],
     ['push', 1],
     ['push', 0],
     ['ifeq', 8],
     ['pop', None],
     ['return', None]],),
   ['inconsistent', 8]),
  ('shallower arm reaching merge first is inconsistent',
   ([['push', 1],
     ['pop', None],
     ['push', 2],
     ['pop', None],
     ['push', 1],
     ['ifeq', 7],
     ['push', 9],
     ['push', 1],
     ['return', None]],),
   ['inconsistent', 7]),
  ('execution falling off the end',
   ([['push', 1], ['pop', None], ['push', 2], ['pop', None], ['push', 1], ['push', 1]],),
   ['falls-off', 5]),
  ('negative branch target',
   ([['push', 1], ['pop', None], ['push', 2], ['pop', None], ['push', 1], ['goto', -1], ['return', None]],),
   ['falls-off', 5]),
  ('swap with one item underflows',
   ([['push', 1], ['pop', None], ['push', 2], ['pop', None], ['push', 1], ['swap', None], ['return', None]],),
   ['underflow', 5])],
 [('dup_x1 with one item underflows',
   ([['push', 1],
     ['pop', None],
     ['push', 2],
     ['pop', None],
     ['push', 3],
     ['pop', None],
     ['push', 1],
     ['dup_x1', None],
     ['return', None]],),
   ['underflow', 7]),
  ('dup_x1 with two items is legal',
   ([['push', 1],
     ['pop', None],
     ['push', 2],
     ['pop', None],
     ['push', 3],
     ['pop', None],
     ['push', 1],
     ['push', 2],
     ['dup_x1', None],
     ['add', None],
     ['add', None],
     ['return', None]],),
   ['ok', 3]),
  ('regression: dead code after goto is not verified',
   ([['push', 1],
     ['pop', None],
     ['push', 2],
     ['pop', None],
     ['push', 3],
     ['pop', None],
     ['push', 1],
     ['goto', 9],
     ['add', None],
     ['return', None]],),
   ['ok', 1]),
  ('if/else arms merge at equal depth',
   ([['push', 1],
     ['pop', None],
     ['push', 2],
     ['pop', None],
     ['push', 3],
     ['pop', None],
     ['push', 0],
     ['ifeq', 10],
     ['push', 5],
     ['goto', 11],
     ['push', 7],
     ['return', None]],),
   ['ok', 1]),
  ('ifeq on empty stack underflows',
   ([['push', 1],
     ['pop', None],
     ['push', 2],
     ['pop', None],
     ['push', 3],
     ['pop', None],
     ['ifeq', 7],
     ['push', 1],
     ['return', None]],),
   ['underflow', 6]),
  ('deeper arm reaching merge first is inconsistent',
   ([['push', 1],
     ['pop', None],
     ['push', 2],
     ['pop', None],
     ['push', 3],
     ['pop', None],
     ['push', 1],
     ['push', 0],
     ['ifeq', 10],
     ['pop', None],
     ['return', None]],),
   ['inconsistent', 10]),
  ('shallower arm reaching merge first is inconsistent',
   ([['push', 1],
     ['pop', None],
     ['push', 2],
     ['pop', None],
     ['push', 3],
     ['pop', None],
     ['push', 1],
     ['ifeq', 9],
     ['push', 9],
     ['push', 1],
     ['return', None]],),
   ['inconsistent', 9]),
  ('execution falling off the end',
   ([['push', 1], ['pop', None], ['push', 2], ['pop', None], ['push', 3], ['pop', None], ['push', 1]],),
   ['falls-off', 6]),
  ('negative branch target',
   ([['push', 1],
     ['pop', None],
     ['push', 2],
     ['pop', None],
     ['push', 3],
     ['pop', None],
     ['push', 1],
     ['goto', -1],
     ['return', None]],),
   ['falls-off', 7]),
  ('swap with one item underflows',
   ([['push', 1],
     ['pop', None],
     ['push', 2],
     ['pop', None],
     ['push', 3],
     ['pop', None],
     ['push', 1],
     ['swap', None],
     ['return', None]],),
   ['underflow', 7])],
 [('dup_x1 with one item underflows',
   ([['push', 1],
     ['pop', None],
     ['push', 2],
     ['pop', None],
     ['push', 3],
     ['pop', None],
     ['push', 4],
     ['pop', None],
     ['push', 1],
     ['dup_x1', None],
     ['return', None]],),
   ['underflow', 9]),
  ('dup_x1 with two items is legal',
   ([['push', 1],
     ['pop', None],
     ['push', 2],
     ['pop', None],
     ['push', 3],
     ['pop', None],
     ['push', 4],
     ['pop', None],
     ['push', 1],
     ['push', 2],
     ['dup_x1', None],
     ['add', None],
     ['add', None],
     ['return', None]],),
   ['ok', 3]),
  ('regression: dead code after goto is not verified',
   ([['push', 1],
     ['pop', None],
     ['push', 2],
     ['pop', None],
     ['push', 3],
     ['pop', None],
     ['push', 4],
     ['pop', None],
     ['push', 1],
     ['goto', 11],
     ['add', None],
     ['return', None]],),
   ['ok', 1]),
  ('if/else arms merge at equal depth',
   ([['push', 1],
     ['pop', None],
     ['push', 2],
     ['pop', None],
     ['push', 3],
     ['pop', None],
     ['push', 4],
     ['pop', None],
     ['push', 0],
     ['ifeq', 12],
     ['push', 5],
     ['goto', 13],
     ['push', 7],
     ['return', None]],),
   ['ok', 1]),
  ('ifeq on empty stack underflows',
   ([['push', 1],
     ['pop', None],
     ['push', 2],
     ['pop', None],
     ['push', 3],
     ['pop', None],
     ['push', 4],
     ['pop', None],
     ['ifeq', 9],
     ['push', 1],
     ['return', None]],),
   ['underflow', 8]),
  ('deeper arm reaching merge first is inconsistent',
   ([['push', 1],
     ['pop', None],
     ['push', 2],
     ['pop', None],
     ['push', 3],
     ['pop', None],
     ['push', 4],
     ['pop', None],
     ['push', 1],
     ['push', 0],
     ['ifeq', 12],
     ['pop', None],
     ['return', None]],),
   ['inconsistent', 12]),
  ('shallower arm reaching merge first is inconsistent',
   ([['push', 1],
     ['pop', None],
     ['push', 2],
     ['pop', None],
     ['push', 3],
     ['pop', None],
     ['push', 4],
     ['pop', None],
     ['push', 1],
     ['ifeq', 11],
     ['push', 9],
     ['push', 1],
     ['return', None]],),
   ['inconsistent', 11]),
  ('execution falling off the end',
   ([['push', 1],
     ['pop', None],
     ['push', 2],
     ['pop', None],
     ['push', 3],
     ['pop', None],
     ['push', 4],
     ['pop', None],
     ['push', 1],
     ['push', 1]],),
   ['falls-off', 9]),
  ('negative branch target',
   ([['push', 1],
     ['pop', None],
     ['push', 2],
     ['pop', None],
     ['push', 3],
     ['pop', None],
     ['push', 4],
     ['pop', None],
     ['push', 1],
     ['goto', -1],
     ['return', None]],),
   ['falls-off', 9]),
  ('swap with one item underflows',
   ([['push', 1],
     ['pop', None],
     ['push', 2],
     ['pop', None],
     ['push', 3],
     ['pop', None],
     ['push', 4],
     ['pop', None],
     ['push', 1],
     ['swap', None],
     ['return', None]],),
   ['underflow', 9])]]
for label, args, expected in cases[N - 1]:
    check(label, solve(*args), expected)
print(json.dumps({"observations": observations, "passed": all(x["passed"] for x in observations)}, ensure_ascii=False))
raise SystemExit(0 if all(x["passed"] for x in observations) else 1)

source:
"""Failure Map reference implementation. Python standard library only."""
import json

N = 1
observations = []
def solve(code):
    effects = {'push': (0, 1), 'pop': (1, -1), 'dup': (1, 1), 'dup_x1': (2, 1), 'swap': (2, 0),
               'add': (2, -1), 'ifeq': (1, -1), 'goto': (0, 0), 'return': (1, -1)}
    def verify():
        depth = {0: 0}
        work = [0]
        maxd = 0
        while work:
            i = work.pop()
            op, arg = code[i]
            need, delta = effects[op]
            d = depth[i]
            if d < need:
                return ['underflow', i]
            nd = d + delta
            maxd = max(maxd, nd)
            if op == 'goto':
                succ = [arg, i + 1] if i + 1 < len(code) else [arg]
            elif op == 'ifeq':
                succ = [i + 1, arg]
            elif op == 'return':
                succ = []
            else:
                succ = [i + 1]
            for s in succ:
                if s < 0 or s >= len(code):
                    return ['falls-off', i]
                if s in depth:
                    if depth[s] != nd:
                        return ['inconsistent', s]
                else:
                    depth[s] = nd
                    work.append(s)
        return ['ok', maxd]
    try:
        return verify()
    except (IndexError, KeyError):
        return ['vm-crash']
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
cases = [[('dup_x1 with one item underflows', ([['push', 1], ['dup_x1', None], ['return', None]],), ['underflow', 1]),
  ('dup_x1 with two items is legal',
   ([['push', 1], ['push', 2], ['dup_x1', None], ['add', None], ['add', None], ['return', None]],),
   ['ok', 3]),
  ('regression: dead code after goto is not verified',
   ([['push', 1], ['goto', 3], ['add', None], ['return', None]],),
   ['ok', 1]),
  ('if/else arms merge at equal depth',
   ([['push', 0], ['ifeq', 4], ['push', 5], ['goto', 5], ['push', 7], ['return', None]],),
   ['ok', 1]),
  ('ifeq on empty stack underflows', ([['ifeq', 1], ['push', 1], ['return', None]],), ['underflow', 0]),
  ('deeper arm reaching merge first is inconsistent',
   ([['push', 1], ['push', 0], ['ifeq', 4], ['pop', None], ['return', None]],),
   ['inconsistent', 4]),
  ('shallower arm reaching merge first is inconsistent',
   ([['push', 1], ['ifeq', 3], ['push', 9], ['push', 1], ['return', None]],),
   ['inconsistent', 3]),
  ('execution falling off the end', ([['push', 1], ['push', 1]],), ['falls-off', 1]),
  ('negative branch target', ([['push', 1], ['goto', -1], ['return', None]],), ['falls-off', 1]),
  ('swap with one item underflows', ([['push', 1], ['swap', None], ['return', None]],), ['underflow', 1])],
 [('dup_x1 with one item underflows',
   ([['push', 1], ['pop', None], ['push', 1], ['dup_x1', None], ['return', None]],),
   ['underflow', 3]),
  ('dup_x1 with two items is legal',
   ([['push', 1],
     ['pop', None],
     ['push', 1],
     ['push', 2],
     ['dup_x1', None],
     ['add', None],
     ['add', None],
     ['return', None]],),
   ['ok', 3]),
  ('regression: dead code after goto is not verified',
   ([['push', 1], ['pop', None], ['push', 1], ['goto', 5], ['add', None], ['return', None]],),
   ['ok', 1]),
  ('if/else arms merge at equal depth',
   ([['push', 1],
     ['pop', None],
     ['push', 0],
     ['ifeq', 6],
     ['push', 5],
     ['goto', 7],
     ['push', 7],
     ['return', None]],),
   ['ok', 1]),
  ('ifeq on empty stack underflows',
   ([['push', 1], ['pop', None], ['ifeq', 3], ['push', 1], ['return', None]],),
   ['underflow', 2]),
  ('deeper arm reaching merge first is inconsistent',
   ([['push', 1], ['pop', None], ['push', 1], ['push', 0], ['ifeq', 6], ['pop', None], ['return', None]],),
   ['inconsistent', 6]),
  ('shallower arm reaching merge first is inconsistent',
   ([['push', 1], ['pop', None], ['push', 1], ['ifeq', 5], ['push', 9], ['push', 1], ['return', None]],),
   ['inconsistent', 5]),
  ('execution falling off the end', ([['push', 1], ['pop', None], ['push', 1]],), ['falls-off', 2]),
  ('negative branch target',
   ([['push', 1], ['pop', None], ['push', 1], ['goto', -1], ['return', None]],),
   ['falls-off', 3]),
  ('swap with one item underflows',
   ([['push', 1], ['pop', None], ['push', 1], ['swap', None], ['return', None]],),
   ['underflow', 3])],
 [('dup_x1 with one item underflows',
   ([['push', 1],
     ['pop', None],
     ['push', 2],
     ['pop', None],
     ['push', 1],
     ['dup_x1', None],
     ['return', None]],),
   ['underflow', 5]),
  ('dup_x1 with two items is legal',
   ([['push', 1],
     ['pop', None],
     ['push', 2],
     ['pop', None],
     ['push', 1],
     ['push', 2],
     ['dup_x1', None],
     ['add', None],
     ['add', None],
     ['return', None]],),
   ['ok', 3]),
  ('regression: dead code after goto is not verified',
   ([['push', 1],
     ['pop', None],
     ['push', 2],
     ['pop', None],
     ['push', 1],
     ['goto', 7],
     ['add', None],
     ['return', None]],),
   ['ok', 1]),
  ('if/else arms merge at equal depth',
   ([['push', 1],
     ['pop', None],
     ['push', 2],
     ['pop', None],
     ['push', 0],
     ['ifeq', 8],
     ['push', 5],
     ['goto', 9],
     ['push', 7],
     ['return', None]],),
   ['ok', 1]),
  ('ifeq on empty stack underflows',
   ([['push', 1], ['pop', None], ['push', 2], ['pop', None], ['ifeq', 5], ['push', 1], ['return', None]],),
   ['underflow', 4]),
  ('deeper arm reaching merge first is inconsistent',
   ([['push', 1],
     ['pop', None],
     ['push', 2],
     ['pop', None],
     ['push', 1],
     ['push', 0],
     ['ifeq', 8],
     ['pop', None],
     ['return', None]],),
   ['inconsistent', 8]),
  ('shallower arm reaching merge first is inconsistent',
   ([['push', 1],
     ['pop', None],
     ['push', 2],
     ['pop', None],
     ['push', 1],
     ['ifeq', 7],
     ['push', 9],
     ['push', 1],
     ['return', None]],),
   ['inconsistent', 7]),
  ('execution falling off the end',
   ([['push', 1], ['pop', None], ['push', 2], ['pop', None], ['push', 1], ['push', 1]],),
   ['falls-off', 5]),
  ('negative branch target',
   ([['push', 1], ['pop', None], ['push', 2], ['pop', None], ['push', 1], ['goto', -1], ['return', None]],),
   ['falls-off', 5]),
  ('swap with one item underflows',
   ([['push', 1], ['pop', None], ['push', 2], ['pop', None], ['push', 1], ['swap', None], ['return', None]],),
   ['underflow', 5])],
 [('dup_x1 with one item underflows',
   ([['push', 1],
     ['pop', None],
     ['push', 2],
     ['pop', None],
     ['push', 3],
     ['pop', None],
     ['push', 1],
     ['dup_x1', None],
     ['return', None]],),
   ['underflow', 7]),
  ('dup_x1 with two items is legal',
   ([['push', 1],
     ['pop', None],
     ['push', 2],
     ['pop', None],
     ['push', 3],
     ['pop', None],
     ['push', 1],
     ['push', 2],
     ['dup_x1', None],
     ['add', None],
     ['add', None],
     ['return', None]],),
   ['ok', 3]),
  ('regression: dead code after goto is not verified',
   ([['push', 1],
     ['pop', None],
     ['push', 2],
     ['pop', None],
     ['push', 3],
     ['pop', None],
     ['push', 1],
     ['goto', 9],
     ['add', None],
     ['return', None]],),
   ['ok', 1]),
  ('if/else arms merge at equal depth',
   ([['push', 1],
     ['pop', None],
     ['push', 2],
     ['pop', None],
     ['push', 3],
     ['pop', None],
     ['push', 0],
     ['ifeq', 10],
     ['push', 5],
     ['goto', 11],
     ['push', 7],
     ['return', None]],),
   ['ok', 1]),
  ('ifeq on empty stack underflows',
   ([['push', 1],
     ['pop', None],
     ['push', 2],
     ['pop', None],
     ['push', 3],
     ['pop', None],
     ['ifeq', 7],
     ['push', 1],
     ['return', None]],),
   ['underflow', 6]),
  ('deeper arm reaching merge first is inconsistent',
   ([['push', 1],
     ['pop', None],
     ['push', 2],
     ['pop', None],
     ['push', 3],
     ['pop', None],
     ['push', 1],
     ['push', 0],
     ['ifeq', 10],
     ['pop', None],
     ['return', None]],),
   ['inconsistent', 10]),
  ('shallower arm reaching merge first is inconsistent',
   ([['push', 1],
     ['pop', None],
     ['push', 2],
     ['pop', None],
     ['push', 3],
     ['pop', None],
     ['push', 1],
     ['ifeq', 9],
     ['push', 9],
     ['push', 1],
     ['return', None]],),
   ['inconsistent', 9]),
  ('execution falling off the end',
   ([['push', 1], ['pop', None], ['push', 2], ['pop', None], ['push', 3], ['pop', None], ['push', 1]],),
   ['falls-off', 6]),
  ('negative branch target',
   ([['push', 1],
     ['pop', None],
     ['push', 2],
     ['pop', None],
     ['push', 3],
     ['pop', None],
     ['push', 1],
     ['goto', -1],
     ['return', None]],),
   ['falls-off', 7]),
  ('swap with one item underflows',
   ([['push', 1],
     ['pop', None],
     ['push', 2],
     ['pop', None],
     ['push', 3],
     ['pop', None],
     ['push', 1],
     ['swap', None],
     ['return', None]],),
   ['underflow', 7])],
 [('dup_x1 with one item underflows',
   ([['push', 1],
     ['pop', None],
     ['push', 2],
     ['pop', None],
     ['push', 3],
     ['pop', None],
     ['push', 4],
     ['pop', None],
     ['push', 1],
     ['dup_x1', None],
     ['return', None]],),
   ['underflow', 9]),
  ('dup_x1 with two items is legal',
   ([['push', 1],
     ['pop', None],
     ['push', 2],
     ['pop', None],
     ['push', 3],
     ['pop', None],
     ['push', 4],
     ['pop', None],
     ['push', 1],
     ['push', 2],
     ['dup_x1', None],
     ['add', None],
     ['add', None],
     ['return', None]],),
   ['ok', 3]),
  ('regression: dead code after goto is not verified',
   ([['push', 1],
     ['pop', None],
     ['push', 2],
     ['pop', None],
     ['push', 3],
     ['pop', None],
     ['push', 4],
     ['pop', None],
     ['push', 1],
     ['goto', 11],
     ['add', None],
     ['return', None]],),
   ['ok', 1]),
  ('if/else arms merge at equal depth',
   ([['push', 1],
     ['pop', None],
     ['push', 2],
     ['pop', None],
     ['push', 3],
     ['pop', None],
     ['push', 4],
     ['pop', None],
     ['push', 0],
     ['ifeq', 12],
     ['push', 5],
     ['goto', 13],
     ['push', 7],
     ['return', None]],),
   ['ok', 1]),
  ('ifeq on empty stack underflows',
   ([['push', 1],
     ['pop', None],
     ['push', 2],
     ['pop', None],
     ['push', 3],
     ['pop', None],
     ['push', 4],
     ['pop', None],
     ['ifeq', 9],
     ['push', 1],
     ['return', None]],),
   ['underflow', 8]),
  ('deeper arm reaching merge first is inconsistent',
   ([['push', 1],
     ['pop', None],
     ['push', 2],
     ['pop', None],
     ['push', 3],
     ['pop', None],
     ['push', 4],
     ['pop', None],
     ['push', 1],
     ['push', 0],
     ['ifeq', 12],
     ['pop', None],
     ['return', None]],),
   ['inconsistent', 12]),
  ('shallower arm reaching merge first is inconsistent',
   ([['push', 1],
     ['pop', None],
     ['push', 2],
     ['pop', None],
     ['push', 3],
     ['pop', None],
     ['push', 4],
     ['pop', None],
     ['push', 1],
     ['ifeq', 11],
     ['push', 9],
     ['push', 1],
     ['return', None]],),
   ['inconsistent', 11]),
  ('execution falling off the end',
   ([['push', 1],
     ['pop', None],
     ['push', 2],
     ['pop', None],
     ['push', 3],
     ['pop', None],
     ['push', 4],
     ['pop', None],
     ['push', 1],
     ['push', 1]],),
   ['falls-off', 9]),
  ('negative branch target',
   ([['push', 1],
     ['pop', None],
     ['push', 2],
     ['pop', None],
     ['push', 3],
     ['pop', None],
     ['push', 4],
     ['pop', None],
     ['push', 1],
     ['goto', -1],
     ['return', None]],),
   ['falls-off', 9]),
  ('swap with one item underflows',
   ([['push', 1],
     ['pop', None],
     ['push', 2],
     ['pop', None],
     ['push', 3],
     ['pop', None],
     ['push', 4],
     ['pop', None],
     ['push', 1],
     ['swap', None],
     ['return', None]],),
   ['underflow', 9])]]
for label, args, expected in cases[N - 1]:
    check(label, solve(*args), expected)
print(json.dumps({"observations": observations, "passed": all(x["passed"] for x in observations)}, ensure_ascii=False))
raise SystemExit(0 if all(x["passed"] for x in observations) else 1)

prompt:
Well-formed methods with dead code after goto are rejected with bogus underflows.

code is a list of [op, arg]. Stack effects (required, delta): push (0,+1), pop (1,-1), dup (1,+1), dup_x1 (2,+1), swap (2,0), add (2,-1), ifeq (1,-1; successors fallthrough and arg), goto (0,0; only arg), return (1,-1; none). Dataflow from index 0 with depth 0: report ["underflow", i], ["falls-off", i] for a successor outside the code, ["inconsistent", s] when a merge sees two depths, else ["ok", max depth]. Unreachable code is never examined.

split: open-access


broken_source:
"""Failure Map reference implementation. Python standard library only."""
import json

N = 1
observations = []
def solve(code):
    effects = {'push': (0, 1), 'pop': (1, -1), 'dup': (1, 1), 'dup_x1': (2, 1), 'swap': (2, 0),
               'add': (2, -1), 'ifeq': (1, 0), 'goto': (0, 0), 'return': (1, -1)}
    def verify():
        depth = {0: 0}
        work = [0]
        maxd = 0
        while work:
            i = work.pop()
            op, arg = code[i]
            need, delta = effects[op]
            d = depth[i]
            if d < need:
                return ['underflow', i]
            nd = d + delta
            maxd = max(maxd, nd)
            if op == 'goto':
                succ = [arg]
            elif op == 'ifeq':
                succ = [i + 1, arg]
            elif op == 'return':
                succ = []
            else:
                succ = [i + 1]
            for s in succ:
                if s < 0 or s >= len(code):
                    return ['falls-off', i]
                if s in depth:
                    if depth[s] != nd:
                        return ['inconsistent', s]
                else:
                    depth[s] = nd
                    work.append(s)
        return ['ok', maxd]
    try:
        return verify()
    except (IndexError, KeyError):
        return ['vm-crash']
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
cases = [[('dup_x1 with one item underflows', ([['push', 1], ['dup_x1', None], ['return', None]],), ['underflow', 1]),
  ('dup_x1 with two items is legal',
   ([['push', 1], ['push', 2], ['dup_x1', None], ['add', None], ['add', None], ['return', None]],),
   ['ok', 3]),
  ('regression: dead code after goto is not verified',
   ([['push', 1], ['goto', 3], ['add', None], ['return', None]],),
   ['ok', 1]),
  ('if/else arms merge at equal depth',
   ([['push', 0], ['ifeq', 4], ['push', 5], ['goto', 5], ['push', 7], ['return', None]],),
   ['ok', 1]),
  ('ifeq on empty stack underflows', ([['ifeq', 1], ['push', 1], ['return', None]],), ['underflow', 0]),
  ('deeper arm reaching merge first is inconsistent',
   ([['push', 1], ['push', 0], ['ifeq', 4], ['pop', None], ['return', None]],),
   ['inconsistent', 4]),
  ('shallower arm reaching merge first is inconsistent',
   ([['push', 1], ['ifeq', 3], ['push', 9], ['push', 1], ['return', None]],),
   ['inconsistent', 3]),
  ('execution falling off the end', ([['push', 1], ['push', 1]],), ['falls-off', 1]),
  ('negative branch target', ([['push', 1], ['goto', -1], ['return', None]],), ['falls-off', 1]),
  ('swap with one item underflows', ([['push', 1], ['swap', None], ['return', None]],), ['underflow', 1])],
 [('dup_x1 with one item underflows',
   ([['push', 1], ['pop', None], ['push', 1], ['dup_x1', None], ['return', None]],),
   ['underflow', 3]),
  ('dup_x1 with two items is legal',
   ([['push', 1],
     ['pop', None],
     ['push', 1],
     ['push', 2],
     ['dup_x1', None],
     ['add', None],
     ['add', None],
     ['return', None]],),
   ['ok', 3]),
  ('regression: dead code after goto is not verified',
   ([['push', 1], ['pop', None], ['push', 1], ['goto', 5], ['add', None], ['return', None]],),
   ['ok', 1]),
  ('if/else arms merge at equal depth',
   ([['push', 1],
     ['pop', None],
     ['push', 0],
     ['ifeq', 6],
     ['push', 5],
     ['goto', 7],
     ['push', 7],
     ['return', None]],),
   ['ok', 1]),
  ('ifeq on empty stack underflows',
   ([['push', 1], ['pop', None], ['ifeq', 3], ['push', 1], ['return', None]],),
   ['underflow', 2]),
  ('deeper arm reaching merge first is inconsistent',
   ([['push', 1], ['pop', None], ['push', 1], ['push', 0], ['ifeq', 6], ['pop', None], ['return', None]],),
   ['inconsistent', 6]),
  ('shallower arm reaching merge first is inconsistent',
   ([['push', 1], ['pop', None], ['push', 1], ['ifeq', 5], ['push', 9], ['push', 1], ['return', None]],),
   ['inconsistent', 5]),
  ('execution falling off the end', ([['push', 1], ['pop', None], ['push', 1]],), ['falls-off', 2]),
  ('negative branch target',
   ([['push', 1], ['pop', None], ['push', 1], ['goto', -1], ['return', None]],),
   ['falls-off', 3]),
  ('swap with one item underflows',
   ([['push', 1], ['pop', None], ['push', 1], ['swap', None], ['return', None]],),
   ['underflow', 3])],
 [('dup_x1 with one item underflows',
   ([['push', 1],
     ['pop', None],
     ['push', 2],
     ['pop', None],
     ['push', 1],
     ['dup_x1', None],
     ['return', None]],),
   ['underflow', 5]),
  ('dup_x1 with two items is legal',
   ([['push', 1],
     ['pop', None],
     ['push', 2],
     ['pop', None],
     ['push', 1],
     ['push', 2],
     ['dup_x1', None],
     ['add', None],
     ['add', None],
     ['return', None]],),
   ['ok', 3]),
  ('regression: dead code after goto is not verified',
   ([['push', 1],
     ['pop', None],
     ['push', 2],
     ['pop', None],
     ['push', 1],
     ['goto', 7],
     ['add', None],
     ['return', None]],),
   ['ok', 1]),
  ('if/else arms merge at equal depth',
   ([['push', 1],
     ['pop', None],
     ['push', 2],
     ['pop', None],
     ['push', 0],
     ['ifeq', 8],
     ['push', 5],
     ['goto', 9],
     ['push', 7],
     ['return', None]],),
   ['ok', 1]),
  ('ifeq on empty stack underflows',
   ([['push', 1], ['pop', None], ['push', 2], ['pop', None], ['ifeq', 5], ['push', 1], ['return', None]],),
   ['underflow', 4]),
  ('deeper arm reaching merge first is inconsistent',
   ([['push', 1],
     ['pop', None],
     ['push', 2],
     ['pop', None],
     ['push', 1],
     ['push', 0],
     ['ifeq', 8],
     ['pop', None],
     ['return', None]],),
   ['inconsistent', 8]),
  ('shallower arm reaching merge first is inconsistent',
   ([['push', 1],
     ['pop', None],
     ['push', 2],
     ['pop', None],
     ['push', 1],
     ['ifeq', 7],
     ['push', 9],
     ['push', 1],
     ['return', None]],),
   ['inconsistent', 7]),
  ('execution falling off the end',
   ([['push', 1], ['pop', None], ['push', 2], ['pop', None], ['push', 1], ['push', 1]],),
   ['falls-off', 5]),
  ('negative branch target',
   ([['push', 1], ['pop', None], ['push', 2], ['pop', None], ['push', 1], ['goto', -1], ['return', None]],),
   ['falls-off', 5]),
  ('swap with one item underflows',
   ([['push', 1], ['pop', None], ['push', 2], ['pop', None], ['push', 1], ['swap', None], ['return', None]],),
   ['underflow', 5])],
 [('dup_x1 with one item underflows',
   ([['push', 1],
     ['pop', None],
     ['push', 2],
     ['pop', None],
     ['push', 3],
     ['pop', None],
     ['push', 1],
     ['dup_x1', None],
     ['return', None]],),
   ['underflow', 7]),
  ('dup_x1 with two items is legal',
   ([['push', 1],
     ['pop', None],
     ['push', 2],
     ['pop', None],
     ['push', 3],
     ['pop', None],
     ['push', 1],
     ['push', 2],
     ['dup_x1', None],
     ['add', None],
     ['add', None],
     ['return', None]],),
   ['ok', 3]),
  ('regression: dead code after goto is not verified',
   ([['push', 1],
     ['pop', None],
     ['push', 2],
     ['pop', None],
     ['push', 3],
     ['pop', None],
     ['push', 1],
     ['goto', 9],
     ['add', None],
     ['return', None]],),
   ['ok', 1]),
  ('if/else arms merge at equal depth',
   ([['push', 1],
     ['pop', None],
     ['push', 2],
     ['pop', None],
     ['push', 3],
     ['pop', None],
     ['push', 0],
     ['ifeq', 10],
     ['push', 5],
     ['goto', 11],
     ['push', 7],
     ['return', None]],),
   ['ok', 1]),
  ('ifeq on empty stack underflows',
   ([['push', 1],
     ['pop', None],
     ['push', 2],
     ['pop', None],
     ['push', 3],
     ['pop', None],
     ['ifeq', 7],
     ['push', 1],
     ['return', None]],),
   ['underflow', 6]),
  ('deeper arm reaching merge first is inconsistent',
   ([['push', 1],
     ['pop', None],
     ['push', 2],
     ['pop', None],
     ['push', 3],
     ['pop', None],
     ['push', 1],
     ['push', 0],
     ['ifeq', 10],
     ['pop', None],
     ['return', None]],),
   ['inconsistent', 10]),
  ('shallower arm reaching merge first is inconsistent',
   ([['push', 1],
     ['pop', None],
     ['push', 2],
     ['pop', None],
     ['push', 3],
     ['pop', None],
     ['push', 1],
     ['ifeq', 9],
     ['push', 9],
     ['push', 1],
     ['return', None]],),
   ['inconsistent', 9]),
  ('execution falling off the end',
   ([['push', 1], ['pop', None], ['push', 2], ['pop', None], ['push', 3], ['pop', None], ['push', 1]],),
   ['falls-off', 6]),
  ('negative branch target',
   ([['push', 1],
     ['pop', None],
     ['push', 2],
     ['pop', None],
     ['push', 3],
     ['pop', None],
     ['push', 1],
     ['goto', -1],
     ['return', None]],),
   ['falls-off', 7]),
  ('swap with one item underflows',
   ([['push', 1],
     ['pop', None],
     ['push', 2],
     ['pop', None],
     ['push', 3],
     ['pop', None],
     ['push', 1],
     ['swap', None],
     ['return', None]],),
   ['underflow', 7])],
 [('dup_x1 with one item underflows',
   ([['push', 1],
     ['pop', None],
     ['push', 2],
     ['pop', None],
     ['push', 3],
     ['pop', None],
     ['push', 4],
     ['pop', None],
     ['push', 1],
     ['dup_x1', None],
     ['return', None]],),
   ['underflow', 9]),
  ('dup_x1 with two items is legal',
   ([['push', 1],
     ['pop', None],
     ['push', 2],
     ['pop', None],
     ['push', 3],
     ['pop', None],
     ['push', 4],
     ['pop', None],
     ['push', 1],
     ['push', 2],
     ['dup_x1', None],
     ['add', None],
     ['add', None],
     ['return', None]],),
   ['ok', 3]),
  ('regression: dead code after goto is not verified',
   ([['push', 1],
     ['pop', None],
     ['push', 2],
     ['pop', None],
     ['push', 3],
     ['pop', None],
     ['push', 4],
     ['pop', None],
     ['push', 1],
     ['goto', 11],
     ['add', None],
     ['return', None]],),
   ['ok', 1]),
  ('if/else arms merge at equal depth',
   ([['push', 1],
     ['pop', None],
     ['push', 2],
     ['pop', None],
     ['push', 3],
     ['pop', None],
     ['push', 4],
     ['pop', None],
     ['push', 0],
     ['ifeq', 12],
     ['push', 5],
     ['goto', 13],
     ['push', 7],
     ['return', None]],),
   ['ok', 1]),
  ('ifeq on empty stack underflows',
   ([['push', 1],
     ['pop', None],
     ['push', 2],
     ['pop', None],
     ['push', 3],
     ['pop', None],
     ['push', 4],
     ['pop', None],
     ['ifeq', 9],
     ['push', 1],
     ['return', None]],),
   ['underflow', 8]),
  ('deeper arm reaching merge first is inconsistent',
   ([['push', 1],
     ['pop', None],
     ['push', 2],
     ['pop', None],
     ['push', 3],
     ['pop', None],
     ['push', 4],
     ['pop', None],
     ['push', 1],
     ['push', 0],
     ['ifeq', 12],
     ['pop', None],
     ['return', None]],),
   ['inconsistent', 12]),
  ('shallower arm reaching merge first is inconsistent',
   ([['push', 1],
     ['pop', None],
     ['push', 2],
     ['pop', None],
     ['push', 3],
     ['pop', None],
     ['push', 4],
     ['pop', None],
     ['push', 1],
     ['ifeq', 11],
     ['push', 9],
     ['push', 1],
     ['return', None]],),
   ['inconsistent', 11]),
  ('execution falling off the end',
   ([['push', 1],
     ['pop', None],
     ['push', 2],
     ['pop', None],
     ['push', 3],
     ['pop', None],
     ['push', 4],
     ['pop', None],
     ['push', 1],
     ['push', 1]],),
   ['falls-off', 9]),
  ('negative branch target',
   ([['push', 1],
     ['pop', None],
     ['push', 2],
     ['pop', None],
     ['push', 3],
     ['pop', None],
     ['push', 4],
     ['pop', None],
     ['push', 1],
     ['goto', -1],
     ['return', None]],),
   ['falls-off', 9]),
  ('swap with one item underflows',
   ([['push', 1],
     ['pop', None],
     ['push', 2],
     ['pop', None],
     ['push', 3],
     ['pop', None],
     ['push', 4],
     ['pop', None],
     ['push', 1],
     ['swap', None],
     ['return', None]],),
   ['underflow', 9])]]
for label, args, expected in cases[N - 1]:
    check(label, solve(*args), expected)
print(json.dumps({"observations": observations, "passed": all(x["passed"] for x in observations)}, ensure_ascii=False))
raise SystemExit(0 if all(x["passed"] for x in observations) else 1)

meaning: Fixture-count band, not measured model difficulty

deps: stdlib

source:
"""Failure Map reference implementation. Python standard library only."""
import json

N = 1
observations = []
def solve(code):
    effects = {'push': (0, 1), 'pop': (1, -1), 'dup': (1, 1), 'dup_x1': (2, 1), 'swap': (2, 0),
               'add': (2, -1), 'ifeq': (0, -1), 'goto': (0, 0), 'return': (1, -1)}
    def verify():
        depth = {0: 0}
        work = [0]
        maxd = 0
        while work:
            i = work.pop()
            op, arg = code[i]
            need, delta = effects[op]
            d = depth[i]
            if d < need:
                return ['underflow', i]
            nd = d + delta
            maxd = max(maxd, nd)
            if op == 'goto':
                succ = [arg]
            elif op == 'ifeq':
                succ = [i + 1, arg]
            elif op == 'return':
                succ = []
            else:
                succ = [i + 1]
            for s in succ:
                if s < 0 or s >= len(code):
                    return ['falls-off', i]
                if s in depth:
                    if depth[s] != nd:
                        return ['inconsistent', s]
                else:
                    depth[s] = nd
                    work.append(s)
        return ['ok', maxd]
    try:
        return verify()
    except (IndexError, KeyError):
        return ['vm-crash']
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
cases = [[('dup_x1 with one item underflows', ([['push', 1], ['dup_x1', None], ['return', None]],), ['underflow', 1]),
  ('dup_x1 with two items is legal',
   ([['push', 1], ['push', 2], ['dup_x1', None], ['add', None], ['add', None], ['return', None]],),
   ['ok', 3]),
  ('regression: dead code after goto is not verified',
   ([['push', 1], ['goto', 3], ['add', None], ['return', None]],),
   ['ok', 1]),
  ('if/else arms merge at equal depth',
   ([['push', 0], ['ifeq', 4], ['push', 5], ['goto', 5], ['push', 7], ['return', None]],),
   ['ok', 1]),
  ('ifeq on empty stack underflows', ([['ifeq', 1], ['push', 1], ['return', None]],), ['underflow', 0]),
  ('deeper arm reaching merge first is inconsistent',
   ([['push', 1], ['push', 0], ['ifeq', 4], ['pop', None], ['return', None]],),
   ['inconsistent', 4]),
  ('shallower arm reaching merge first is inconsistent',
   ([['push', 1], ['ifeq', 3], ['push', 9], ['push', 1], ['return', None]],),
   ['inconsistent', 3]),
  ('execution falling off the end', ([['push', 1], ['push', 1]],), ['falls-off', 1]),
  ('negative branch target', ([['push', 1], ['goto', -1], ['return', None]],), ['falls-off', 1]),
  ('swap with one item underflows', ([['push', 1], ['swap', None], ['return', None]],), ['underflow', 1])],
 [('dup_x1 with one item underflows',
   ([['push', 1], ['pop', None], ['push', 1], ['dup_x1', None], ['return', None]],),
   ['underflow', 3]),
  ('dup_x1 with two items is legal',
   ([['push', 1],
     ['pop', None],
     ['push', 1],
     ['push', 2],
     ['dup_x1', None],
     ['add', None],
     ['add', None],
     ['return', None]],),
   ['ok', 3]),
  ('regression: dead code after goto is not verified',
   ([['push', 1], ['pop', None], ['push', 1], ['goto', 5], ['add', None], ['return', None]],),
   ['ok', 1]),
  ('if/else arms merge at equal depth',
   ([['push', 1],
     ['pop', None],
     ['push', 0],
     ['ifeq', 6],
     ['push', 5],
     ['goto', 7],
     ['push', 7],
     ['return', None]],),
   ['ok', 1]),
  ('ifeq on empty stack underflows',
   ([['push', 1], ['pop', None], ['ifeq', 3], ['push', 1], ['return', None]],),
   ['underflow', 2]),
  ('deeper arm reaching merge first is inconsistent',
   ([['push', 1], ['pop', None], ['push', 1], ['push', 0], ['ifeq', 6], ['pop', None], ['return', None]],),
   ['inconsistent', 6]),
  ('shallower arm reaching merge first is inconsistent',
   ([['push', 1], ['pop', None], ['push', 1], ['ifeq', 5], ['push', 9], ['push', 1], ['return', None]],),
   ['inconsistent', 5]),
  ('execution falling off the end', ([['push', 1], ['pop', None], ['push', 1]],), ['falls-off', 2]),
  ('negative branch target',
   ([['push', 1], ['pop', None], ['push', 1], ['goto', -1], ['return', None]],),
   ['falls-off', 3]),
  ('swap with one item underflows',
   ([['push', 1], ['pop', None], ['push', 1], ['swap', None], ['return', None]],),
   ['underflow', 3])],
 [('dup_x1 with one item underflows',
   ([['push', 1],
     ['pop', None],
     ['push', 2],
     ['pop', None],
     ['push', 1],
     ['dup_x1', None],
     ['return', None]],),
   ['underflow', 5]),
  ('dup_x1 with two items is legal',
   ([['push', 1],
     ['pop', None],
     ['push', 2],
     ['pop', None],
     ['push', 1],
     ['push', 2],
     ['dup_x1', None],
     ['add', None],
     ['add', None],
     ['return', None]],),
   ['ok', 3]),
  ('regression: dead code after goto is not verified',
   ([['push', 1],
     ['pop', None],
     ['push', 2],
     ['pop', None],
     ['push', 1],
     ['goto', 7],
     ['add', None],
     ['return', None]],),
   ['ok', 1]),
  ('if/else arms merge at equal depth',
   ([['push', 1],
     ['pop', None],
     ['push', 2],
     ['pop', None],
     ['push', 0],
     ['ifeq', 8],
     ['push', 5],
     ['goto', 9],
     ['push', 7],
     ['return', None]],),
   ['ok', 1]),
  ('ifeq on empty stack underflows',
   ([['push', 1], ['pop', None], ['push', 2], ['pop', None], ['ifeq', 5], ['push', 1], ['return', None]],),
   ['underflow', 4]),
  ('deeper arm reaching merge first is inconsistent',
   ([['push', 1],
     ['pop', None],
     ['push', 2],
     ['pop', None],
     ['push', 1],
     ['push', 0],
     ['ifeq', 8],
     ['pop', None],
     ['return', None]],),
   ['inconsistent', 8]),
  ('shallower arm reaching merge first is inconsistent',
   ([['push', 1],
     ['pop', None],
     ['push', 2],
     ['pop', None],
     ['push', 1],
     ['ifeq', 7],
     ['push', 9],
     ['push', 1],
     ['return', None]],),
   ['inconsistent', 7]),
  ('execution falling off the end',
   ([['push', 1], ['pop', None], ['push', 2], ['pop', None], ['push', 1], ['push', 1]],),
   ['falls-off', 5]),
  ('negative branch target',
   ([['push', 1], ['pop', None], ['push', 2], ['pop', None], ['push', 1], ['goto', -1], ['return', None]],),
   ['falls-off', 5]),
  ('swap with one item underflows',
   ([['push', 1], ['pop', None], ['push', 2], ['pop', None], ['push', 1], ['swap', None], ['return', None]],),
   ['underflow', 5])],
 [('dup_x1 with one item underflows',
   ([['push', 1],
     ['pop', None],
     ['push', 2],
     ['pop', None],
     ['push', 3],
     ['pop', None],
     ['push', 1],
     ['dup_x1', None],
     ['return', None]],),
   ['underflow', 7]),
  ('dup_x1 with two items is legal',
   ([['push', 1],
     ['pop', None],
     ['push', 2],
     ['pop', None],
     ['push', 3],
     ['pop', None],
     ['push', 1],
     ['push', 2],
     ['dup_x1', None],
     ['add', None],
     ['add', None],
     ['return', None]],),
   ['ok', 3]),
  ('regression: dead code after goto is not verified',
   ([['push', 1],
     ['pop', None],
     ['push', 2],
     ['pop', None],
     ['push', 3],
     ['pop', None],
     ['push', 1],
     ['goto', 9],
     ['add', None],
     ['return', None]],),
   ['ok', 1]),
  ('if/else arms merge at equal depth',
   ([['push', 1],
     ['pop', None],
     ['push', 2],
     ['pop', None],
     ['push', 3],
     ['pop', None],
     ['push', 0],
     ['ifeq', 10],
     ['push', 5],
     ['goto', 11],
     ['push', 7],
     ['return', None]],),
   ['ok', 1]),
  ('ifeq on empty stack underflows',
   ([['push', 1],
     ['pop', None],
     ['push', 2],
     ['pop', None],
     ['push', 3],
     ['pop', None],
     ['ifeq', 7],
     ['push', 1],
     ['return', None]],),
   ['underflow', 6]),
  ('deeper arm reaching merge first is inconsistent',
   ([['push', 1],
     ['pop', None],
     ['push', 2],
     ['pop', None],
     ['push', 3],
     ['pop', None],
     ['push', 1],
     ['push', 0],
     ['ifeq', 10],
     ['pop', None],
     ['return', None]],),
   ['inconsistent', 10]),
  ('shallower arm reaching merge first is inconsistent',
   ([['push', 1],
     ['pop', None],
     ['push', 2],
     ['pop', None],
     ['push', 3],
     ['pop', None],
     ['push', 1],
     ['ifeq', 9],
     ['push', 9],
     ['push', 1],
     ['return', None]],),
   ['inconsistent', 9]),
  ('execution falling off the end',
   ([['push', 1], ['pop', None], ['push', 2], ['pop', None], ['push', 3], ['pop', None], ['push', 1]],),
   ['falls-off', 6]),
  ('negative branch target',
   ([['push', 1],
     ['pop', None],
     ['push', 2],
     ['pop', None],
     ['push', 3],
     ['pop', None],
     ['push', 1],
     ['goto', -1],
     ['return', None]],),
   ['falls-off', 7]),
  ('swap with one item underflows',
   ([['push', 1],
     ['pop', None],
     ['push', 2],
     ['pop', None],
     ['push', 3],
     ['pop', None],
     ['push', 1],
     ['swap', None],
     ['return', None]],),
   ['underflow', 7])],
 [('dup_x1 with one item underflows',
   ([['push', 1],
     ['pop', None],
     ['push', 2],
     ['pop', None],
     ['push', 3],
     ['pop', None],
     ['push', 4],
     ['pop', None],
     ['push', 1],
     ['dup_x1', None],
     ['return', None]],),
   ['underflow', 9]),
  ('dup_x1 with two items is legal',
   ([['push', 1],
     ['pop', None],
     ['push', 2],
     ['pop', None],
     ['push', 3],
     ['pop', None],
     ['push', 4],
     ['pop', None],
     ['push', 1],
     ['push', 2],
     ['dup_x1', None],
     ['add', None],
     ['add', None],
     ['return', None]],),
   ['ok', 3]),
  ('regression: dead code after goto is not verified',
   ([['push', 1],
     ['pop', None],
     ['push', 2],
     ['pop', None],
     ['push', 3],
     ['pop', None],
     ['push', 4],
     ['pop', None],
     ['push', 1],
     ['goto', 11],
     ['add', None],
     ['return', None]],),
   ['ok', 1]),
  ('if/else arms merge at equal depth',
   ([['push', 1],
     ['pop', None],
     ['push', 2],
     ['pop', None],
     ['push', 3],
     ['pop', None],
     ['push', 4],
     ['pop', None],
     ['push', 0],
     ['ifeq', 12],
     ['push', 5],
     ['goto', 13],
     ['push', 7],
     ['return', None]],),
   ['ok', 1]),
  ('ifeq on empty stack underflows',
   ([['push', 1],
     ['pop', None],
     ['push', 2],
     ['pop', None],
     ['push', 3],
     ['pop', None],
     ['push', 4],
     ['pop', None],
     ['ifeq', 9],
     ['push', 1],
     ['return', None]],),
   ['underflow', 8]),
  ('deeper arm reaching merge first is inconsistent',
   ([['push', 1],
     ['pop', None],
     ['push', 2],
     ['pop', None],
     ['push', 3],
     ['pop', None],
     ['push', 4],
     ['pop', None],
     ['push', 1],
     ['push', 0],
     ['ifeq', 12],
     ['pop', None],
     ['return', None]],),
   ['inconsistent', 12]),
  ('shallower arm reaching merge first is inconsistent',
   ([['push', 1],
     ['pop', None],
     ['push', 2],
     ['pop', None],
     ['push', 3],
     ['pop', None],
     ['push', 4],
     ['pop', None],
     ['push', 1],
     ['ifeq', 11],
     ['push', 9],
     ['push', 1],
     ['return', None]],),
   ['inconsistent', 11]),
  ('execution falling off the end',
   ([['push', 1],
     ['pop', None],
     ['push', 2],
     ['pop', None],
     ['push', 3],
     ['pop', None],
     ['push', 4],
     ['pop', None],
     ['push', 1],
     ['push', 1]],),
   ['falls-off', 9]),
  ('negative branch target',
   ([['push', 1],
     ['pop', None],
     ['push', 2],
     ['pop', None],
     ['push', 3],
     ['pop', None],
     ['push', 4],
     ['pop', None],
     ['push', 1],
     ['goto', -1],
     ['return', None]],),
   ['falls-off', 9]),
  ('swap with one item underflows',
   ([['push', 1],
     ['pop', None],
     ['push', 2],
     ['pop', None],
     ['push', 3],
     ['pop', None],
     ['push', 4],
     ['pop', None],
     ['push', 1],
     ['swap', None],
     ['return', None]],),
   ['underflow', 9])]]
for label, args, expected in cases[N - 1]:
    check(label, solve(*args), expected)
print(json.dumps({"observations": observations, "passed": all(x["passed"] for x in observations)}, ensure_ascii=False))
raise SystemExit(0 if all(x["passed"] for x in observations) else 1)

prompt:
Both branch targets are verified one slot too deep and max stack is overstated.

code is a list of [op, arg]. Stack effects (required, delta): push (0,+1), pop (1,-1), dup (1,+1), dup_x1 (2,+1), swap (2,0), add (2,-1), ifeq (1,-1; successors fallthrough and arg), goto (0,0; only arg), return (1,-1; none). Dataflow from index 0 with depth 0: report ["underflow", i], ["falls-off", i] for a successor outside the code, ["inconsistent", s] when a merge sees two depths, else ["ok", max depth]. Unreachable code is never examined.

split: open-access


broken_source:
"""Failure Map reference implementation. Python standard library only."""
import json

N = 1
observations = []
def solve(code):
    effects = {'push': (0, 1), 'pop': (1, -1), 'dup': (1, 1), 'dup_x1': (2, 1), 'swap': (2, 0),
               'add': (2, -1), 'ifeq': (1, -1), 'goto': (0, 0), 'return': (1, -1)}
    def verify():
        depth = {0: 0}
        work = [0]
        maxd = 0
        while work:
            i = work.pop()
            op, arg = code[i]
            need, delta = effects[op]
            d = depth[i]
            if d < need:
                return ['underflow', i]
            nd = d + delta
            maxd = max(maxd, nd)
            if op == 'goto':
                succ = [arg]
            elif op == 'ifeq':
                succ = [i + 1, arg]
            elif op == 'return':
                succ = []
            else:
                succ = [i + 1]
            for s in succ:
                if s < 0 or s >= len(code):
                    return ['falls-off', i]
                if s in depth:
                    if depth[s] < nd:
                        return ['inconsistent', s]
                else:
                    depth[s] = nd
                    work.append(s)
        return ['ok', maxd]
    try:
        return verify()
    except (IndexError, KeyError):
        return ['vm-crash']
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
cases = [[('dup_x1 with one item underflows', ([['push', 1], ['dup_x1', None], ['return', None]],), ['underflow', 1]),
  ('dup_x1 with two items is legal',
   ([['push', 1], ['push', 2], ['dup_x1', None], ['add', None], ['add', None], ['return', None]],),
   ['ok', 3]),
  ('regression: dead code after goto is not verified',
   ([['push', 1], ['goto', 3], ['add', None], ['return', None]],),
   ['ok', 1]),
  ('if/else arms merge at equal depth',
   ([['push', 0], ['ifeq', 4], ['push', 5], ['goto', 5], ['push', 7], ['return', None]],),
   ['ok', 1]),
  ('ifeq on empty stack underflows', ([['ifeq', 1], ['push', 1], ['return', None]],), ['underflow', 0]),
  ('deeper arm reaching merge first is inconsistent',
   ([['push', 1], ['push', 0], ['ifeq', 4], ['pop', None], ['return', None]],),
   ['inconsistent', 4]),
  ('shallower arm reaching merge first is inconsistent',
   ([['push', 1], ['ifeq', 3], ['push', 9], ['push', 1], ['return', None]],),
   ['inconsistent', 3]),
  ('execution falling off the end', ([['push', 1], ['push', 1]],), ['falls-off', 1]),
  ('negative branch target', ([['push', 1], ['goto', -1], ['return', None]],), ['falls-off', 1]),
  ('swap with one item underflows', ([['push', 1], ['swap', None], ['return', None]],), ['underflow', 1])],
 [('dup_x1 with one item underflows',
   ([['push', 1], ['pop', None], ['push', 1], ['dup_x1', None], ['return', None]],),
   ['underflow', 3]),
  ('dup_x1 with two items is legal',
   ([['push', 1],
     ['pop', None],
     ['push', 1],
     ['push', 2],
     ['dup_x1', None],
     ['add', None],
     ['add', None],
     ['return', None]],),
   ['ok', 3]),
  ('regression: dead code after goto is not verified',
   ([['push', 1], ['pop', None], ['push', 1], ['goto', 5], ['add', None], ['return', None]],),
   ['ok', 1]),
  ('if/else arms merge at equal depth',
   ([['push', 1],
     ['pop', None],
     ['push', 0],
     ['ifeq', 6],
     ['push', 5],
     ['goto', 7],
     ['push', 7],
     ['return', None]],),
   ['ok', 1]),
  ('ifeq on empty stack underflows',
   ([['push', 1], ['pop', None], ['ifeq', 3], ['push', 1], ['return', None]],),
   ['underflow', 2]),
  ('deeper arm reaching merge first is inconsistent',
   ([['push', 1], ['pop', None], ['push', 1], ['push', 0], ['ifeq', 6], ['pop', None], ['return', None]],),
   ['inconsistent', 6]),
  ('shallower arm reaching merge first is inconsistent',
   ([['push', 1], ['pop', None], ['push', 1], ['ifeq', 5], ['push', 9], ['push', 1], ['return', None]],),
   ['inconsistent', 5]),
  ('execution falling off the end', ([['push', 1], ['pop', None], ['push', 1]],), ['falls-off', 2]),
  ('negative branch target',
   ([['push', 1], ['pop', None], ['push', 1], ['goto', -1], ['return', None]],),
   ['falls-off', 3]),
  ('swap with one item underflows',
   ([['push', 1], ['pop', None], ['push', 1], ['swap', None], ['return', None]],),
   ['underflow', 3])],
 [('dup_x1 with one item underflows',
   ([['push', 1],
     ['pop', None],
     ['push', 2],
     ['pop', None],
     ['push', 1],
     ['dup_x1', None],
     ['return', None]],),
   ['underflow', 5]),
  ('dup_x1 with two items is legal',
   ([['push', 1],
     ['pop', None],
     ['push', 2],
     ['pop', None],
     ['push', 1],
     ['push', 2],
     ['dup_x1', None],
     ['add', None],
     ['add', None],
     ['return', None]],),
   ['ok', 3]),
  ('regression: dead code after goto is not verified',
   ([['push', 1],
     ['pop', None],
     ['push', 2],
     ['pop', None],
     ['push', 1],
     ['goto', 7],
     ['add', None],
     ['return', None]],),
   ['ok', 1]),
  ('if/else arms merge at equal depth',
   ([['push', 1],
     ['pop', None],
     ['push', 2],
     ['pop', None],
     ['push', 0],
     ['ifeq', 8],
     ['push', 5],
     ['goto', 9],
     ['push', 7],
     ['return', None]],),
   ['ok', 1]),
  ('ifeq on empty stack underflows',
   ([['push', 1], ['pop', None], ['push', 2], ['pop', None], ['ifeq', 5], ['push', 1], ['return', None]],),
   ['underflow', 4]),
  ('deeper arm reaching merge first is inconsistent',
   ([['push', 1],
     ['pop', None],
     ['push', 2],
     ['pop', None],
     ['push', 1],
     ['push', 0],
     ['ifeq', 8],
     ['pop', None],
     ['return', None]],),
   ['inconsistent', 8]),
  ('shallower arm reaching merge first is inconsistent',
   ([['push', 1],
     ['pop', None],
     ['push', 2],
     ['pop', None],
     ['push', 1],
     ['ifeq', 7],
     ['push', 9],
     ['push', 1],
     ['return', None]],),
   ['inconsistent', 7]),
  ('execution falling off the end',
   ([['push', 1], ['pop', None], ['push', 2], ['pop', None], ['push', 1], ['push', 1]],),
   ['falls-off', 5]),
  ('negative branch target',
   ([['push', 1], ['pop', None], ['push', 2], ['pop', None], ['push', 1], ['goto', -1], ['return', None]],),
   ['falls-off', 5]),
  ('swap with one item underflows',
   ([['push', 1], ['pop', None], ['push', 2], ['pop', None], ['push', 1], ['swap', None], ['return', None]],),
   ['underflow', 5])],
 [('dup_x1 with one item underflows',
   ([['push', 1],
     ['pop', None],
     ['push', 2],
     ['pop', None],
     ['push', 3],
     ['pop', None],
     ['push', 1],
     ['dup_x1', None],
     ['return', None]],),
   ['underflow', 7]),
  ('dup_x1 with two items is legal',
   ([['push', 1],
     ['pop', None],
     ['push', 2],
     ['pop', None],
     ['push', 3],
     ['pop', None],
     ['push', 1],
     ['push', 2],
     ['dup_x1', None],
     ['add', None],
     ['add', None],
     ['return', None]],),
   ['ok', 3]),
  ('regression: dead code after goto is not verified',
   ([['push', 1],
     ['pop', None],
     ['push', 2],
     ['pop', None],
     ['push', 3],
     ['pop', None],
     ['push', 1],
     ['goto', 9],
     ['add', None],
     ['return', None]],),
   ['ok', 1]),
  ('if/else arms merge at equal depth',
   ([['push', 1],
     ['pop', None],
     ['push', 2],
     ['pop', None],
     ['push', 3],
     ['pop', None],
     ['push', 0],
     ['ifeq', 10],
     ['push', 5],
     ['goto', 11],
     ['push', 7],
     ['return', None]],),
   ['ok', 1]),
  ('ifeq on empty stack underflows',
   ([['push', 1],
     ['pop', None],
     ['push', 2],
     ['pop', None],
     ['push', 3],
     ['pop', None],
     ['ifeq', 7],
     ['push', 1],
     ['return', None]],),
   ['underflow', 6]),
  ('deeper arm reaching merge first is inconsistent',
   ([['push', 1],
     ['pop', None],
     ['push', 2],
     ['pop', None],
     ['push', 3],
     ['pop', None],
     ['push', 1],
     ['push', 0],
     ['ifeq', 10],
     ['pop', None],
     ['return', None]],),
   ['inconsistent', 10]),
  ('shallower arm reaching merge first is inconsistent',
   ([['push', 1],
     ['pop', None],
     ['push', 2],
     ['pop', None],
     ['push', 3],
     ['pop', None],
     ['push', 1],
     ['ifeq', 9],
     ['push', 9],
     ['push', 1],
     ['return', None]],),
   ['inconsistent', 9]),
  ('execution falling off the end',
   ([['push', 1], ['pop', None], ['push', 2], ['pop', None], ['push', 3], ['pop', None], ['push', 1]],),
   ['falls-off', 6]),
  ('negative branch target',
   ([['push', 1],
     ['pop', None],
     ['push', 2],
     ['pop', None],
     ['push', 3],
     ['pop', None],
     ['push', 1],
     ['goto', -1],
     ['return', None]],),
   ['falls-off', 7]),
  ('swap with one item underflows',
   ([['push', 1],
     ['pop', None],
     ['push', 2],
     ['pop', None],
     ['push', 3],
     ['pop', None],
     ['push', 1],
     ['swap', None],
     ['return', None]],),
   ['underflow', 7])],
 [('dup_x1 with one item underflows',
   ([['push', 1],
     ['pop', None],
     ['push', 2],
     ['pop', None],
     ['push', 3],
     ['pop', None],
     ['push', 4],
     ['pop', None],
     ['push', 1],
     ['dup_x1', None],
     ['return', None]],),
   ['underflow', 9]),
  ('dup_x1 with two items is legal',
   ([['push', 1],
     ['pop', None],
     ['push', 2],
     ['pop', None],
     ['push', 3],
     ['pop', None],
     ['push', 4],
     ['pop', None],
     ['push', 1],
     ['push', 2],
     ['dup_x1', None],
     ['add', None],
     ['add', None],
     ['return', None]],),
   ['ok', 3]),
  ('regression: dead code after goto is not verified',
   ([['push', 1],
     ['pop', None],
     ['push', 2],
     ['pop', None],
     ['push', 3],
     ['pop', None],
     ['push', 4],
     ['pop', None],
     ['push', 1],
     ['goto', 11],
     ['add', None],
     ['return', None]],),
   ['ok', 1]),
  ('if/else arms merge at equal depth',
   ([['push', 1],
     ['pop', None],
     ['push', 2],
     ['pop', None],
     ['push', 3],
     ['pop', None],
     ['push', 4],
     ['pop', None],
     ['push', 0],
     ['ifeq', 12],
     ['push', 5],
     ['goto', 13],
     ['push', 7],
     ['return', None]],),
   ['ok', 1]),
  ('ifeq on empty stack underflows',
   ([['push', 1],
     ['pop', None],
     ['push', 2],
     ['pop', None],
     ['push', 3],
     ['pop', None],
     ['push', 4],
     ['pop', None],
     ['ifeq', 9],
     ['push', 1],
     ['return', None]],),
   ['underflow', 8]),
  ('deeper arm reaching merge first is inconsistent',
   ([['push', 1],
     ['pop', None],
     ['push', 2],
     ['pop', None],
     ['push', 3],
     ['pop', None],
     ['push', 4],
     ['pop', None],
     ['push', 1],
     ['push', 0],
     ['ifeq', 12],
     ['pop', None],
     ['return', None]],),
   ['inconsistent', 12]),
  ('shallower arm reaching merge first is inconsistent',
   ([['push', 1],
     ['pop', None],
     ['push', 2],
     ['pop', None],
     ['push', 3],
     ['pop', None],
     ['push', 4],
     ['pop', None],
     ['push', 1],
     ['ifeq', 11],
     ['push', 9],
     ['push', 1],
     ['return', None]],),
   ['inconsistent', 11]),
  ('execution falling off the end',
   ([['push', 1],
     ['pop', None],
     ['push', 2],
     ['pop', None],
     ['push', 3],
     ['pop', None],
     ['push', 4],
     ['pop', None],
     ['push', 1],
     ['push', 1]],),
   ['falls-off', 9]),
  ('negative branch target',
   ([['push', 1],
     ['pop', None],
     ['push', 2],
     ['pop', None],
     ['push', 3],
     ['pop', None],
     ['push', 4],
     ['pop', None],
     ['push', 1],
     ['goto', -1],
     ['return', None]],),
   ['falls-off', 9]),
  ('swap with one item underflows',
   ([['push', 1],
     ['pop', None],
     ['push', 2],
     ['pop', None],
     ['push', 3],
     ['pop', None],
     ['push', 4],
     ['pop', None],
     ['push', 1],
     ['swap', None],
     ['return', None]],),
   ['underflow', 9])]]
for label, args, expected in cases[N - 1]:
    check(label, solve(*args), expected)
print(json.dumps({"observations": observations, "passed": all(x["passed"] for x in observations)}, ensure_ascii=False))
raise SystemExit(0 if all(x["passed"] for x in observations) else 1)

source:
"""Failure Map reference implementation. Python standard library only."""
import json

N = 1
observations = []
def solve(code):
    effects = {'push': (0, 1), 'pop': (1, -1), 'dup': (1, 1), 'dup_x1': (2, 1), 'swap': (2, 0),
               'add': (2, -1), 'ifeq': (1, -1), 'goto': (0, 0), 'return': (1, -1)}
    def verify():
        depth = {0: 0}
        work = [0]
        maxd = 0
        while work:
            i = work.pop()
            op, arg = code[i]
            need, delta = effects[op]
            d = depth[i]
            if d < need:
                return ['underflow', i]
            nd = d + delta
            maxd = max(maxd, nd)
            if op == 'goto':
                succ = [arg]
            elif op == 'ifeq':
                succ = [i + 1, arg]
            elif op == 'return':
                succ = []
            else:
                succ = [i + 1]
            for s in succ:
                if s < 0 or s >= len(code):
                    return ['falls-off', i]
                if s in depth:
                    if abs(depth[s] - nd) > 1:
                        return ['inconsistent', s]
                else:
                    depth[s] = nd
                    work.append(s)
        return ['ok', maxd]
    try:
        return verify()
    except (IndexError, KeyError):
        return ['vm-crash']
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
cases = [[('dup_x1 with one item underflows', ([['push', 1], ['dup_x1', None], ['return', None]],), ['underflow', 1]),
  ('dup_x1 with two items is legal',
   ([['push', 1], ['push', 2], ['dup_x1', None], ['add', None], ['add', None], ['return', None]],),
   ['ok', 3]),
  ('regression: dead code after goto is not verified',
   ([['push', 1], ['goto', 3], ['add', None], ['return', None]],),
   ['ok', 1]),
  ('if/else arms merge at equal depth',
   ([['push', 0], ['ifeq', 4], ['push', 5], ['goto', 5], ['push', 7], ['return', None]],),
   ['ok', 1]),
  ('ifeq on empty stack underflows', ([['ifeq', 1], ['push', 1], ['return', None]],), ['underflow', 0]),
  ('deeper arm reaching merge first is inconsistent',
   ([['push', 1], ['push', 0], ['ifeq', 4], ['pop', None], ['return', None]],),
   ['inconsistent', 4]),
  ('shallower arm reaching merge first is inconsistent',
   ([['push', 1], ['ifeq', 3], ['push', 9], ['push', 1], ['return', None]],),
   ['inconsistent', 3]),
  ('execution falling off the end', ([['push', 1], ['push', 1]],), ['falls-off', 1]),
  ('negative branch target', ([['push', 1], ['goto', -1], ['return', None]],), ['falls-off', 1]),
  ('swap with one item underflows', ([['push', 1], ['swap', None], ['return', None]],), ['underflow', 1])],
 [('dup_x1 with one item underflows',
   ([['push', 1], ['pop', None], ['push', 1], ['dup_x1', None], ['return', None]],),
   ['underflow', 3]),
  ('dup_x1 with two items is legal',
   ([['push', 1],
     ['pop', None],
     ['push', 1],
     ['push', 2],
     ['dup_x1', None],
     ['add', None],
     ['add', None],
     ['return', None]],),
   ['ok', 3]),
  ('regression: dead code after goto is not verified',
   ([['push', 1], ['pop', None], ['push', 1], ['goto', 5], ['add', None], ['return', None]],),
   ['ok', 1]),
  ('if/else arms merge at equal depth',
   ([['push', 1],
     ['pop', None],
     ['push', 0],
     ['ifeq', 6],
     ['push', 5],
     ['goto', 7],
     ['push', 7],
     ['return', None]],),
   ['ok', 1]),
  ('ifeq on empty stack underflows',
   ([['push', 1], ['pop', None], ['ifeq', 3], ['push', 1], ['return', None]],),
   ['underflow', 2]),
  ('deeper arm reaching merge first is inconsistent',
   ([['push', 1], ['pop', None], ['push', 1], ['push', 0], ['ifeq', 6], ['pop', None], ['return', None]],),
   ['inconsistent', 6]),
  ('shallower arm reaching merge first is inconsistent',
   ([['push', 1], ['pop', None], ['push', 1], ['ifeq', 5], ['push', 9], ['push', 1], ['return', None]],),
   ['inconsistent', 5]),
  ('execution falling off the end', ([['push', 1], ['pop', None], ['push', 1]],), ['falls-off', 2]),
  ('negative branch target',
   ([['push', 1], ['pop', None], ['push', 1], ['goto', -1], ['return', None]],),
   ['falls-off', 3]),
  ('swap with one item underflows',
   ([['push', 1], ['pop', None], ['push', 1], ['swap', None], ['return', None]],),
   ['underflow', 3])],
 [('dup_x1 with one item underflows',
   ([['push', 1],
     ['pop', None],
     ['push', 2],
     ['pop', None],
     ['push', 1],
     ['dup_x1', None],
     ['return', None]],),
   ['underflow', 5]),
  ('dup_x1 with two items is legal',
   ([['push', 1],
     ['pop', None],
     ['push', 2],
     ['pop', None],
     ['push', 1],
     ['push', 2],
     ['dup_x1', None],
     ['add', None],
     ['add', None],
     ['return', None]],),
   ['ok', 3]),
  ('regression: dead code after goto is not verified',
   ([['push', 1],
     ['pop', None],
     ['push', 2],
     ['pop', None],
     ['push', 1],
     ['goto', 7],
     ['add', None],
     ['return', None]],),
   ['ok', 1]),
  ('if/else arms merge at equal depth',
   ([['push', 1],
     ['pop', None],
     ['push', 2],
     ['pop', None],
     ['push', 0],
     ['ifeq', 8],
     ['push', 5],
     ['goto', 9],
     ['push', 7],
     ['return', None]],),
   ['ok', 1]),
  ('ifeq on empty stack underflows',
   ([['push', 1], ['pop', None], ['push', 2], ['pop', None], ['ifeq', 5], ['push', 1], ['return', None]],),
   ['underflow', 4]),
  ('deeper arm reaching merge first is inconsistent',
   ([['push', 1],
     ['pop', None],
     ['push', 2],
     ['pop', None],
     ['push', 1],
     ['push', 0],
     ['ifeq', 8],
     ['pop', None],
     ['return', None]],),
   ['inconsistent', 8]),
  ('shallower arm reaching merge first is inconsistent',
   ([['push', 1],
     ['pop', None],
     ['push', 2],
     ['pop', None],
     ['push', 1],
     ['ifeq', 7],
     ['push', 9],
     ['push', 1],
     ['return', None]],),
   ['inconsistent', 7]),
  ('execution falling off the end',
   ([['push', 1], ['pop', None], ['push', 2], ['pop', None], ['push', 1], ['push', 1]],),
   ['falls-off', 5]),
  ('negative branch target',
   ([['push', 1], ['pop', None], ['push', 2], ['pop', None], ['push', 1], ['goto', -1], ['return', None]],),
   ['falls-off', 5]),
  ('swap with one item underflows',
   ([['push', 1], ['pop', None], ['push', 2], ['pop', None], ['push', 1], ['swap', None], ['return', None]],),
   ['underflow', 5])],
 [('dup_x1 with one item underflows',
   ([['push', 1],
     ['pop', None],
     ['push', 2],
     ['pop', None],
     ['push', 3],
     ['pop', None],
     ['push', 1],
     ['dup_x1', None],
     ['return', None]],),
   ['underflow', 7]),
  ('dup_x1 with two items is legal',
   ([['push', 1],
     ['pop', None],
     ['push', 2],
     ['pop', None],
     ['push', 3],
     ['pop', None],
     ['push', 1],
     ['push', 2],
     ['dup_x1', None],
     ['add', None],
     ['add', None],
     ['return', None]],),
   ['ok', 3]),
  ('regression: dead code after goto is not verified',
   ([['push', 1],
     ['pop', None],
     ['push', 2],
     ['pop', None],
     ['push', 3],
     ['pop', None],
     ['push', 1],
     ['goto', 9],
     ['add', None],
     ['return', None]],),
   ['ok', 1]),
  ('if/else arms merge at equal depth',
   ([['push', 1],
     ['pop', None],
     ['push', 2],
     ['pop', None],
     ['push', 3],
     ['pop', None],
     ['push', 0],
     ['ifeq', 10],
     ['push', 5],
     ['goto', 11],
     ['push', 7],
     ['return', None]],),
   ['ok', 1]),
  ('ifeq on empty stack underflows',
   ([['push', 1],
     ['pop', None],
     ['push', 2],
     ['pop', None],
     ['push', 3],
     ['pop', None],
     ['ifeq', 7],
     ['push', 1],
     ['return', None]],),
   ['underflow', 6]),
  ('deeper arm reaching merge first is inconsistent',
   ([['push', 1],
     ['pop', None],
     ['push', 2],
     ['pop', None],
     ['push', 3],
     ['pop', None],
     ['push', 1],
     ['push', 0],
     ['ifeq', 10],
     ['pop', None],
     ['return', None]],),
   ['inconsistent', 10]),
  ('shallower arm reaching merge first is inconsistent',
   ([['push', 1],
     ['pop', None],
     ['push', 2],
     ['pop', None],
     ['push', 3],
     ['pop', None],
     ['push', 1],
     ['ifeq', 9],
     ['push', 9],
     ['push', 1],
     ['return', None]],),
   ['inconsistent', 9]),
  ('execution falling off the end',
   ([['push', 1], ['pop', None], ['push', 2], ['pop', None], ['push', 3], ['pop', None], ['push', 1]],),
   ['falls-off', 6]),
  ('negative branch target',
   ([['push', 1],
     ['pop', None],
     ['push', 2],
     ['pop', None],
     ['push', 3],
     ['pop', None],
     ['push', 1],
     ['goto', -1],
     ['return', None]],),
   ['falls-off', 7]),
  ('swap with one item underflows',
   ([['push', 1],
     ['pop', None],
     ['push', 2],
     ['pop', None],
     ['push', 3],
     ['pop', None],
     ['push', 1],
     ['swap', None],
     ['return', None]],),
   ['underflow', 7])],
 [('dup_x1 with one item underflows',
   ([['push', 1],
     ['pop', None],
     ['push', 2],
     ['pop', None],
     ['push', 3],
     ['pop', None],
     ['push', 4],
     ['pop', None],
     ['push', 1],
     ['dup_x1', None],
     ['return', None]],),
   ['underflow', 9]),
  ('dup_x1 with two items is legal',
   ([['push', 1],
     ['pop', None],
     ['push', 2],
     ['pop', None],
     ['push', 3],
     ['pop', None],
     ['push', 4],
     ['pop', None],
     ['push', 1],
     ['push', 2],
     ['dup_x1', None],
     ['add', None],
     ['add', None],
     ['return', None]],),
   ['ok', 3]),
  ('regression: dead code after goto is not verified',
   ([['push', 1],
     ['pop', None],
     ['push', 2],
     ['pop', None],
     ['push', 3],
     ['pop', None],
     ['push', 4],
     ['pop', None],
     ['push', 1],
     ['goto', 11],
     ['add', None],
     ['return', None]],),
   ['ok', 1]),
  ('if/else arms merge at equal depth',
   ([['push', 1],
     ['pop', None],
     ['push', 2],
     ['pop', None],
     ['push', 3],
     ['pop', None],
     ['push', 4],
     ['pop', None],
     ['push', 0],
     ['ifeq', 12],
     ['push', 5],
     ['goto', 13],
     ['push', 7],
     ['return', None]],),
   ['ok', 1]),
  ('ifeq on empty stack underflows',
   ([['push', 1],
     ['pop', None],
     ['push', 2],
     ['pop', None],
     ['push', 3],
     ['pop', None],
     ['push', 4],
     ['pop', None],
     ['ifeq', 9],
     ['push', 1],
     ['return', None]],),
   ['underflow', 8]),
  ('deeper arm reaching merge first is inconsistent',
   ([['push', 1],
     ['pop', None],
     ['push', 2],
     ['pop', None],
     ['push', 3],
     ['pop', None],
     ['push', 4],
     ['pop', None],
     ['push', 1],
     ['push', 0],
     ['ifeq', 12],
     ['pop', None],
     ['return', None]],),
   ['inconsistent', 12]),
  ('shallower arm reaching merge first is inconsistent',
   ([['push', 1],
     ['pop', None],
     ['push', 2],
     ['pop', None],
     ['push', 3],
     ['pop', None],
     ['push', 4],
     ['pop', None],
     ['push', 1],
     ['ifeq', 11],
     ['push', 9],
     ['push', 1],
     ['return', None]],),
   ['inconsistent', 11]),
  ('execution falling off the end',
   ([['push', 1],
     ['pop', None],
     ['push', 2],
     ['pop', None],
     ['push', 3],
     ['pop', None],
     ['push', 4],
     ['pop', None],
     ['push', 1],
     ['push', 1]],),
   ['falls-off', 9]),
  ('negative branch target',
   ([['push', 1],
     ['pop', None],
     ['push', 2],
     ['pop', None],
     ['push', 3],
     ['pop', None],
     ['push', 4],
     ['pop', None],
     ['push', 1],
     ['goto', -1],
     ['return', None]],),
   ['falls-off', 9]),
  ('swap with one item underflows',
   ([['push', 1],
     ['pop', None],
     ['push', 2],
     ['pop', None],
     ['push', 3],
     ['pop', None],
     ['push', 4],
     ['pop', None],
     ['push', 1],
     ['swap', None],
     ['return', None]],),
   ['underflow', 9])]]
for label, args, expected in cases[N - 1]:
    check(label, solve(*args), expected)
print(json.dumps({"observations": observations, "passed": all(x["passed"] for x in observations)}, ensure_ascii=False))
raise SystemExit(0 if all(x["passed"] for x in observations) else 1)

prompt:
A control-flow merge reached with a shallower stack on the second path is accepted.

code is a list of [op, arg]. Stack effects (required, delta): push (0,+1), pop (1,-1), dup (1,+1), dup_x1 (2,+1), swap (2,0), add (2,-1), ifeq (1,-1; successors fallthrough and arg), goto (0,0; only arg), return (1,-1; none). Dataflow from index 0 with depth 0: report ["underflow", i], ["falls-off", i] for a successor outside the code, ["inconsistent", s] when a merge sees two depths, else ["ok", max depth]. Unreachable code is never examined.

split: open-access