[Bug 78468] Compiling of shader gets stuck in infinite loop

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=78468

--- Comment #13 from Iago Toral <itoral at igalia.com> ---
FWIW, I can reproduce the problem with a simple fragment shader like this one:

#version 140

uniform sampler2D tex;
out vec4 FragColor;

void main()
{
   vec4 col = texture(tex, vec2(0, 0));  // 1
   for (int i=0; i<30; i++)              // 2
      col += vec4(0.1, 0.1, 0.1, 0.1);   // 3
   col = vec4(col.rgb/ 2.0, col.a);      // 4
   FragColor = col;                      // 5
}

Some things worth noting:

- The hang goes away if I only replace (1) by:
     vec4 col = vec4(0, 0, 0, 0);
  or even something like this
     vec4 col = vec4(texture(tex, vec2(0, 0)).r, 0.0, 0.0, 0.0);

- The hang goes away if I only replace (4) by:
   col = vec4(col.rgb, col.a);

- The hang goes away if we reduce the number of iterations in the loop below a
certain threshold. Actually, for some thresholds you can see that it seems to
hang, but will eventually finished after a few seconds. It just seems that the
time required to complete the constant_folding optimization pass grows
exponentially with the number of iterations in the cases where the test seems
to hang.

-- 
You are receiving this mail because:
You are the QA Contact for the bug.
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.freedesktop.org/archives/intel-3d-bugs/attachments/20140910/49571c02/attachment.html>