[Bug 111241] Shadertoy shader causing hang

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=111241

Timothy Arceri <t_arceri at yahoo.com.au> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |RESOLVED
         Resolution|---                         |FIXED

--- Comment #13 from Timothy Arceri <t_arceri at yahoo.com.au> ---
(In reply to Dieter Nützel from comment #12)
> (In reply to Pierre-Eric Pelloux-Prayer from comment #11)
> > (In reply to Dieter Nützel from comment #8)
> > > BTW
> > > 
> > > Pierre-Eric can you look into this
> > > 
> > > Shadertoy shader corruption, too?
> > > https://www.shadertoy.com/view/Xt3cWS
> > >
> > 
> > The "Buffer A" shader doesn't write fragColor when uv.y is < 0.1 or > 0.9.
> > 
> > So the content is undefined and may be black on some platform or random.
> > 
> > radeonsi is correct here, but we might want to replace undef values with 0x0
> > to get a default value instead of random.
> 
> Cool to have you around for bug hunting...;-)
> 
> Any hints where I shoud change 'undef values with 0x0' for testing?
> 
> And sorry that I 'hijacked' this thread - should I open a new ticket?

I don't think you need to open a bug for it at all. As its not a bug in Mesa
its a shader bug.

Closing this bug report as it should be fixed by:

commit  47cc660d9c19572e5ef2dce7c8ae1766a2ac9885
glsl: replace 'x + (-x)' with constant 0
   This fixes a hang in shadertoy for radeonsi where a buffer was initialized
with:

   value -= value

   with value being undefined.
   In this case LLVM replace the operation with an assignment to NaN.

   Cc: 19.1 19.2 <mesa-stable at lists.freedesktop.org>
   Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=111241
   Reviewed-by: Marek Olšák <marek.olsak at amd.com>

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