add line bisector tool

tools/bisect_pair_lines.py

@@ -0,0 +1,63 @@
+'''
+Given two similar files, for example one with an additional optimization pass,
+and with different results, will bisect between them to find the smallest
+diff that makes the outputs different.
+Unlike bisect_pairs, this uses lines instead of diffs. We replace line by line. This assumes
+the programs differ on each line but lines have not been added or removed
+'''
+
+import os, sys, shutil
+from subprocess import Popen, PIPE, STDOUT
+
+__rootpath__ = os.path.abspath(os.path.dirname(os.path.dirname(__file__)))
+def path_from_root(*pathelems):
+  return os.path.join(__rootpath__, *pathelems)
+exec(open(path_from_root('tools', 'shared.py'), 'r').read())
+
+file1 = open(sys.argv[1]).read()
+file2 = open(sys.argv[2]).read()
+
+leftf = open('left', 'w')
+leftf.write(file1)
+leftf.close()
+
+rightf = open('right', 'w')
+rightf.write(file2)
+rightf.close()
+
+def run_code(name):
+  ret = run_js(name, stderr=PIPE, full_output=True)
+  # fix stack traces
+  ret = filter(lambda line: not line.startswith('    at ') and not name in line, ret.split('\n'))
+  return '\n'.join(ret)
+
+print 'running files'
+left_result = run_code('left')
+right_result = run_code('right') # right as in left-right, not as in correct
+assert left_result != right_result
+
+low = 0
+high = file1.count('\n')
+
+print 'beginning bisection, %d lines' % high
+
+left_lines = file1.split('\n')
+right_lines = file2.split('\n')
+
+while True:
+  mid = int((low + high)/2)
+  print low, high, '  current: %d' % mid,
+  open('middle', 'w').write('\n'.join(left_lines[:mid] + right_lines[mid:]))
+  shutil.copyfile('middle', 'middle' + str(mid))
+  result = run_code('middle')
+  print result == left_result, result == right_result#, 'XXX', left_result, 'YYY', result, 'ZZZ', right_result
+  if mid == low or mid == high: break
+  if result == right_result:
+    low = mid
+  elif result == left_result:
+    high = mid
+  else:
+    raise Exception('new result!?!?')
+
+print 'middle%d is like left, middle%d is like right' % (mid+1, mid)
+