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

[Michael Gottesman]

Sure. Lets assume that you are debugging InstCombine. You put a counter into InstCombine that is triggered by lets say the flag -max-instcombine-counter=<foo>

Then you take the test case and run it for different values of N, stopping instcombine at N and while you are waiting, grab some coffee = ).

Michael

On Aug 1, 2014, at 6:54 PM, Chad Rosier <mcrosier at codeaurora.org> wrote:

> 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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>> 
> 
> 
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