[Mesa-dev] [PATCH (resend)] r600/sb: Don't require array declarations for TGSI_FILE_SYSTEM_VALUE

[Gert Wollny]

Am Freitag, den 02.02.2018, 06:56 -0500 schrieb Ilia Mirkin:
> On Fri, Feb 2, 2018 at 4:07 AM, Gert Wollny <gw.fossdev at gmail.com>
> wrote:
> > Am Freitag, den 02.02.2018, 09:04 +0100 schrieb Roland Scheidegger:
> > > 
> > > 
> > > Yes, the _GL spec_ says it is an array.
> > > But in gallium it can't be. Therefore I think it's incorrect if
> > > we
> > > end up with array accesses there (albeit I was too lazy to
> > > actually
> > > look at the tgsi, but I'm pretty sure it isn't declard as an
> > > array).
> > 
> > the TGSI for the relevant shader in the piglit looks like this:
> > 
> > FRAG
> > DCL SV[0], SAMPLEMASK
> > DCL OUT[0], COLOR
> > DCL CONST[0][0]
> > DCL TEMP[0..1], LOCAL
> > DCL ADDR[0]
> > IMM[0] FLT32 {    1.0000,     0.0000,     0.0000,     0.0000}
> > IMM[1] INT32 {1, 0, 0, 0}
> >   0: MOV TEMP[0], IMM[0].xyyx
> >   1: UARL ADDR[0].x, CONST[0][0].xxxx
> >   2: USEQ TEMP[1].x, SV[ADDR[0].x].xxxx, IMM[1].xxxx
> 
> OK, this is a big problem. I'm guessing the GLSL code was something
> like
> 
> gl_SampleMaskIn[uniform]
> 
This is how the piglit is written, and the standard definess
gl_SampleMaskIn is defined as an array, so this makes sense. 

> What this got translated into was an indirect access into the *global
> implicit array of system values*. We don't want that. glsl_to_tgsi
> should just be dropping the indirect access entirely.
Just found this comment in mesa/st/st_glsl_to.tgsi.cpp:6495

 "TODO: If we ever support more than 32 samples, this will have
   to become an array." 

which would imply to me that in this stage the indirect access might at
one point become relevant. 
   
Best, 
Gert