[Mesa-dev] GLSL compiler bug

[Ian Romanick]

On 04/10/2013 12:20 PM, Vadim Girlin wrote:
> Hi,
>
> It seems there is a bug in the compiler. The problem may be reproduced
> with the following shader (complete shader_test file attached):
>
>      void main()
>      {
>          float f = 0.0;
>          while (true) {
>              f = 1.0;
>              break;
>              f = 0.5;
>          }
>          gl_FragColor = vec4(1.0 - f, f, 0.0, 1.0);
>      }
>
> The result of compilation is equal to:
>
>      while (true) {
>          break;
>      }
>      gl_FragColor = vec4(1.0, 0.0, 0.0, 1.0);
>
> In other words, GLSL compiler eliminates both assignments to "f" in the
> loop body and the resulting value of the "f" variable is 0.

Blarg.  I can believe it.  The loop analysis code is a disaster.  Part 
of the reason I'm (slowly) making changes to the IR is so that we can do 
more credible loop handling.

I probably won't be able to get to this problem for quite some time. :(

> Vadim
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