[Mesa-dev] [PATCH 2/2] i965/fs: Add support for gl_HelperInvocation system value.

[Matt Turner]

On Fri, Nov 13, 2015 at 6:05 PM, Matt Turner <mattst88 at gmail.com> wrote:
> ---
> This code generates
>
>         mov(1)          f0<1>UW         g1.14<0,1,0>UW
>         mov(8)          g2<1>UD         0x00000000UD
>         (+f0) sel(8)    g3<1>D          g2<8,8,1>D      -1D
>
> which I don't love because it uses the flag register, and likely uses
> of gl_HelperInvocation will be in an if condition, in which case we
> could have just used f0 directly.
>
> Alternative implementation ideas:
>
>   - Shift dispatch mask with a vector-immediate, and then
>     resolve it to true/false with -(x & 1):
>
>         shr(8)  tmp<1>UW  g1.14<1,8,0>UB  0x76543210V

I got this working (needed to read g1.28, not g1.24) modulo one yet
unexplained issue. Once that is fixed, I'll send a replacement for
this patch.