[LLVMdev] llvm-stress for fuzzing llvm

[Sean Silva]

I'm finding it useful to replace the main loop with:
  for (unsigned i = 0, n = SizeCL/Modifiers.size(); i < n; ++i) {
      Modifiers[i%Modifiers.size()]->Act();
  }

That way, changing the size by 1 adds exactly one instruction, which makes
delta debugging MUCH easier. Maybe it would be worth changing?

--Sean Silva

On Sun, Feb 26, 2012 at 9:23 PM, Sean Silva <silvas at purdue.edu> wrote:

> Wow, nifty tool! I've already found a couple crashes!
>
> It is also really easy to pinpoint what is causing the error. Whenever you
> trigger a bug, run llvm-stress with the same seed but a really small size
> that doesn't trigger the bug (e.g. like 10). Then do binary search on the
> size. Eventually you find exactly the cutoff of size that triggers the bug
> (e.g. 539 runs fine, but 540 crashes), and then you can diff the crashing
> and non-crashing .ll files and there should only be a tiny difference.
>
> --Sean Silva
>
>
> On Sun, Feb 26, 2012 at 7:29 PM, Hal Finkel <hfinkel at anl.gov> wrote:
>
>> Nadav,
>>
>> Thanks, this is neat! Here is a patch which optionally enables
>> generation of the other floating-point types. Please review.
>>
>>  -Hal
>>
>> On Sun, 26 Feb 2012 11:51:04 +0000
>> "Rotem, Nadav" <nadav.rotem at intel.com> wrote:
>>
>> > Hi,
>> >
>> > Compiling lots of 'junk' helps in catching bugs.  I added a new tool
>> > (located under llvm/tools/llvm-stress) for generating random LL
>> > files.  The tool can be used to test different llvm components using
>> > various compilation flags.  Until now, I only found bugs in the
>> > codegen, and not in general llvm optimizations. This probably means
>> > that the generated tests are currently too simple for the
>> > higher-level optimizations.
>> >
>> > The command line below generates a random ll file, and llc compiles
>> > this file. It often crashes.
>> >
>> > ./llvm-stress -seed $RANDOM -o tmp.ll -size 1000 ; ./llc tmp.ll
>> > -mcpu=corei7-avx -mattr=+avx -o /dev/null
>> >
>> > The "-seed" flag sets the initial seed to be used by the random
>> > function.  I implemented a simple portable 'random' function so that
>> > the result should be identical on all platforms. The initial seed
>> > also appears in the name of the generated function.  The "-size"
>> > parameter sets the size of the generated random file.
>> >
>> > Nadav
>> > ---------------------------------------------------------------------
>> > Intel Israel (74) Limited
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>>
>>
>> --
>> Hal Finkel
>> Postdoctoral Appointee
>> Leadership Computing Facility
>> Argonne National Laboratory
>>
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