[llvm] r214610 - Add a small utility called bisect that enables commandline bisecting on a counter.

[Chad Rosier]

Michael,
Can you provide a specific example of how this is used?  I'm sure it's a
very useful tool, but I still don't full understand it's utility.

 Chad

> Author: mgottesman
> Date: Fri Aug  1 20:39:08 2014
> New Revision: 214610
>
> URL: http://llvm.org/viewvc/llvm-project?rev=214610&view=rev
> Log:
> Add a small utility called bisect that enables commandline bisecting on a
> counter.
>
> This is something that I have found to be very useful in my work and I
> wanted to contribute it back to the community since several people in
> the past have asked me for something along these lines. (Jakob, I know
> this has been a while coming ; )]
>
> The way you use this is you create a script that takes in as its first
> argument a count. The script passes into LLVM the count via a command
> line flag that disables a pass after LLVM has run after the pass has
> run for count number of times. Then the script invokes a test of some
> sort and indicates whether LLVM successfully compiled the test via the
> scripts exit status. Then you invoke bisect as follows:
>
> bisect --start=<start_num> --end=<end_num> ./script.sh "%(count)s"
>
> And bisect will continually call ./script.sh with various counts using
> the exit status to determine success and failure.
>
> Added:
>     llvm/trunk/utils/bisect   (with props)
>
> Added: llvm/trunk/utils/bisect
> URL:
> http://llvm.org/viewvc/llvm-project/llvm/trunk/utils/bisect?rev=214610&view=auto
> ==============================================================================
> --- llvm/trunk/utils/bisect (added)
> +++ llvm/trunk/utils/bisect Fri Aug  1 20:39:08 2014
> @@ -0,0 +1,37 @@
> +#!/usr/bin/env python
> +
> +import os
> +import sys
> +import argparse
> +import subprocess
> +
> +parser = argparse.ArgumentParser()
> +
> +parser.add_argument('--start', type=int, default=0)
> +parser.add_argument('--end', type=int, default=(1 << 32))
> +parser.add_argument('command', nargs='+')
> +
> +args = parser.parse_args()
> +
> +start = args.start
> +end = args.end
> +
> +print("Bisect Starting!")
> +print("Start: %d" % start)
> +print("End: %d" % end)
> +
> +last = None
> +while start != end and start != end-1:
> +    count = start + (end - start)/2
> +    print("Visiting Count: %d with (Start, End) = (%d,%d)" % (count,
> start, end))
> +    cmd = [x % {'count':count} for x in args.command]
> +    print cmd
> +    result = subprocess.call(cmd)
> +    if result == 0:
> +        print("    PASSES! Setting start to count")
> +        start = count
> +    else:
> +        print("    FAILS! Setting end to count")
> +        end = count
> +
> +print("Last good count: %d" % start)
>
> Propchange: llvm/trunk/utils/bisect
> ------------------------------------------------------------------------------
>     svn:executable = *
>
>
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