[Mesa-dev] Allowing the reading of outputs for some drivers

[Vadim Girlin]

Hi,

I found some problem with glsl_to_tgsi: remove_output_reads function.
It's replacing outputs with temps, producing incorrect results with
relative addressing. You can see it e.g. with
"vs-varying-array-mat2-col-rd.shader_test". Here is a dump:

> VERT
> DCL IN[0]
> DCL OUT[0], POSITION
> DCL OUT[1], GENERIC[12]
> DCL OUT[2], GENERIC[13]
> DCL OUT[3], GENERIC[14]
> DCL OUT[4], GENERIC[15]
> DCL OUT[5], GENERIC[16]
> DCL OUT[6], GENERIC[17]
> DCL OUT[7], GENERIC[18]
> DCL CONST[0..5]
> DCL TEMP[0..1]
> DCL ADDR[0]
> IMM FLT32 {    1.0000,     2.0000,     3.0000,     4.0000}
> IMM FLT32 {    5.0000,     6.0000,     7.0000,     8.0000}
> IMM FLT32 {    9.0000,    10.0000,    11.0000,    12.0000}
> IMM FLT32 {    0.0000,     1.0000,     0.0000,     0.0000}
>   0: MUL TEMP[0], CONST[2], IN[0].xxxx
>   1: MAD TEMP[1], CONST[3], IN[0].yyyy, TEMP[0]
>   2: MAD TEMP[1], CONST[4], IN[0].zzzz, TEMP[1]
>   3: MAD OUT[0], CONST[5], IN[0].wwww, TEMP[1]
>   4: MOV OUT[2], IMM[0].xyyy
>   5: MOV OUT[3], IMM[0].zwww
>   6: MOV TEMP[0], IMM[1].xyyy

OUT[2-7] is a "varying mat2x2[3] m;", OUT[4] is replaced with the temp
in the instruction 6.

>   7: MOV OUT[5], IMM[1].zwww
>   8: MOV OUT[6], IMM[2].xyyy
>   9: MOV OUT[7], IMM[2].zwww
>  10: ARL ADDR[0].x, CONST[1].xxxx
>  11: SNE TEMP[1], TEMP[ADDR[0].x].xyyy, CONST[0].xyyy

Instruction 11 contains the read with the relative addressing using
this temp, which is incorrect.

I'm not sure how to fix it, but AFAICS at least for r600g this step
could be skipped completely - r600 can read outputs without any
problem, they are located in the general-purpose registers. Removing
calls to remove_output_reads and assert(src.File != TGSI_FILE_OUTPUT)
in the ureg_emit_src produces correct result and test passes on
evergreen (total number of fixed tests is about 60).

Probably it makes sense to make this step optional and ask the driver
whether to use it, if I'm not missing something?

Vadim