create_ladder_graph.py

#!/usr/bin/env python
"""A ladder graph creation program.

This is a python program that creates c source code that will generate
CFGs that are ladder graphs.  Ladder graphs are generally the worst case
for a lot of dominance related algorithms (Dominance frontiers, etc),
and often generate N^2 or worse behavior.

One good use of this program is to test whether your linear time algorithm is
really behaving linearly.
"""

from __future__ import print_function

import argparse
def main():
  parser = argparse.ArgumentParser(description=__doc__)
  parser.add_argument('rungs', type=int,
                      help="Number of ladder rungs. Must be a multiple of 2")
  args = parser.parse_args()
  if (args.rungs % 2) != 0:
    print("Rungs must be a multiple of 2")
    return
  print("int ladder(int *foo, int *bar, int x) {")
  rung1 = range(0, args.rungs, 2)
  rung2 = range(1, args.rungs, 2)
  for i in rung1:
    print("rung1%d:" % i)
    print("*foo = x++;")
    if i != rung1[-1]:
      print("if (*bar) goto rung1%d;" % (i+2))
      print("else goto rung2%d;" % (i+1))
    else:
      print("goto rung2%d;" % (i+1))
  for i in rung2:
    print("rung2%d:" % i)
    print("*foo = x++;")
    if i != rung2[-1]:
      print("goto rung2%d;" % (i+2))
    else:
      print("return *foo;")
  print("}")

if __name__ == '__main__':
  main()