[Mesa-dev] [PATCH] mesa/st: glsl_to_tgsi: Dissolve arrays who's elements are only accessed directly

[Gert Wollny]

Am Montag, den 27.11.2017, 12:14 +0100 schrieb Gert Wollny:
> Am Sonntag, den 26.11.2017, 18:01 -0800 schrieb Eric Anholt:
> > 
> > 
> > This looks like something that should be done with (at most) a
> > small change to opt_array_splitting.cpp, rather than reimplementing
> > it here.
> 
> It seems that the reason the arrays are not split there is that in
> the case of the given piglits, the arrays are accessed in loops, and
> only because the loops are completely unrolled (on r600), the array
> elements are then no longer addressed indirectly and can be split.


> 
> Since I have not yet looked at that part of the code I wonder now 
> whether it one can simply move the "optimize_split_arrays" step past
> the loop unrolling, or whether one should duplicate that step. 

Okay, now I see that the optimization is run various times, so it is
not clear to me why the array is not split in 
glsl-1.50/execution/geometry/max-input-components

There the array that doesn't get split is declared like 

in blk {
  float f[min(gl_MaxGeometryInputComponents,   
              gl_MaxVertexOutputComponents)];
} ins[];

The typical IR for the element access then looks like this 

(if 
 (expression bool != (array_ref 
                      (record_ref 
                       (array_ref 
                        (var_ref ins) 
                         (constant int (4)) 
                        )  
                      f) 
                     (constant int (81)) ) 
                       (constant float (4082.000000)) ) (
        (assign  (x) (var_ref ok)  (constant bool (0)) ) 
      )
      ())

in TGSI this is. 

  FSNE TEMP[851].x := ARRAY(1)[81].xxxx, IMM[83].xxxx
 
i.e. direct addressing. 


If I understand the comments in opt_array_splitting, arrays of arrays
are not properly handled there. Curretly, I don't see how I can fix
this, because I simply didn't look at any code there before. 

Best, 
Gert