[Mesa-dev] [PATCH 8/8 v2] i965: Enable EXT_shader_samples_identical

[Ian Romanick]

On 11/19/2015 09:34 AM, Neil Roberts wrote:
> Jason Ekstrand <jason at jlekstrand.net> writes:
> 
>> On Nov 18, 2015 6:38 PM, "Ian Romanick" <idr at freedesktop.org> wrote:
>>>
>>> From: Ian Romanick <ian.d.romanick at intel.com>
>>>
>>> v2: Handle immediate value for MCS smarter.  Rebase on changes to
>>> nir_texop_sampels_identical (missing second parameter).  Suggested by
>>> Jason.  This still doesn't handle the 16x MSAA case.
> 
> 16x MSAA has a field in the program sampler key because it needs a new
> instruction to fetch from the texture. For 16x MSAA it just uses two of
> the registers that are returned by the MCS fetch instruction instead of
> just one. Maybe you could do something like this:
> 
>       if (mcs.file == BRW_IMMEDIATE_VALUE) {
>          bld.MOV(dst, fs_reg(0));
>       } else if ((key_tex->msaa_16 & (1 << sampler))) {
>          fs_reg tmp = vgrf(glsl_type::uint_type);
>          bld.OR(tmp, mcs, offset(mcs, bld, 1));
>          bld.CMP(dst, tmp, src_reg(0u), BRW_CONDITIONAL_EQ);
>       } else {
>          bld.CMP(dst, mcs, src_reg(0u), BRW_CONDITIONAL_EQ);
>       }
> 
> I tested this on my SKL and it passes all of your Piglit tests. The
> optimiser quite neatly removes the second instruction and the temporary
> register in the 16x case and makes the OR directly update the flag
> registers, so it is possibly the same cost as the 8x case in practice.

I was looking at the msaa_16 flags last night after I sent out v2.  I
was thinking of something along these lines.  Am I correct that nothing
special is needed in the vec4 backend?  It seems like mcs should know
the register size, and the CMP with 0 should just do the right thing.

I'll add your code to the FS and your S-o-b to the commit message... and
hopefully this can land soon. :)

> I can confirm that I've already pushed the 16x MSAA patches to master.
> 
> Regards,
> - Neil