[Mesa-dev] [PATCH] i965/fs: Use UW-typed immediate in multiply inst.

[Neil Roberts]

Looks good to me. Thanks for fixing this. I guess I still have more to
learn about the ISA.

However, should we not also fix the vec4 version? With that,

Reviewed-by: Neil Roberts <neil at linux.intel.com>

If we wanted to play safe and avoid the MUL, we could change it to this
and still avoid having a temporary:

      /* addr = (((sampler << 8) | sampler) +
       *         base_binding_table_index) & 0xfff
       */
      brw_SHL(p, addr, sampler_reg, brw_imm_ud(8u));
      brw_OR(p, addr, addr, sampler_reg);

I just thought the MUL trick was more fun. I'm not sure which would be
faster. The SHL+OR might take up fewer clock cycles but it also
introduces a bubble because it is writing to a register and then
immediately reading from it in the next instruction.

On the other hand it's probably really not worth worrying about
optimising this bit of code because literally nothing is using it in
shader-db. We can just go with whatever works.

Regards,
- Neil

Matt Turner <mattst88 at gmail.com> writes:

> Some hardware reads only the low 16-bits even if the type is UD, but
> other hardware like Cherryview can't handle this.
>
> Fixes spec at arb_gpu_shader5@execution at sampler_array_indexing@fs-simple on
> Cherryview.
> ---
>  src/mesa/drivers/dri/i965/brw_fs_generator.cpp | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/src/mesa/drivers/dri/i965/brw_fs_generator.cpp b/src/mesa/drivers/dri/i965/brw_fs_generator.cpp
> index 40a3db3..ff05b2a 100644
> --- a/src/mesa/drivers/dri/i965/brw_fs_generator.cpp
> +++ b/src/mesa/drivers/dri/i965/brw_fs_generator.cpp
> @@ -788,7 +788,7 @@ fs_generator::generate_tex(fs_inst *inst, struct brw_reg dst, struct brw_reg src
>        brw_set_default_access_mode(p, BRW_ALIGN_1);
>  
>        /* addr = ((sampler * 0x101) + base_binding_table_index) & 0xfff */
> -      brw_MUL(p, addr, sampler_reg, brw_imm_ud(0x101));
> +      brw_MUL(p, addr, sampler_reg, brw_imm_uw(0x101));
>        if (base_binding_table_index)
>           brw_ADD(p, addr, addr, brw_imm_ud(base_binding_table_index));
>        brw_AND(p, addr, addr, brw_imm_ud(0xfff));
> -- 
> 2.3.6
>
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