llvm/utils/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.
"""

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 = xrange(0, args.rungs, 2)
  rung2 = xrange(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()