[LLVMdev] llvm-stress for fuzzing llvm

[Sean Silva]

Here is that patch.

Btw, I've just been using bugpoint, and it's really nifty!

--Sean Silva

2012/2/27 Rotem, Nadav <nadav.rotem at intel.com>

> Sean,
>
> Thanks for looking at this.  Knowing that the last instruction triggered
> the bug is often not enough.  I use bugpoint to reduce the failing test.
>  The reason is that some of the bugs may be caused by the interaction
> between several instruction.  Having said that, I think that the change
> that you proposed is a good one.  Can you send a patch ?
>
> Thanks,
> Nadav
>
>
> From: Sean Silva [mailto:silvas at purdue.edu]
> Sent: Monday, February 27, 2012 05:45
> To: Hal Finkel
> Cc: Rotem, Nadav; llvmdev at cs.uiuc.edu
> Subject: Re: [LLVMdev] llvm-stress for fuzzing llvm
>
> 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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