[Mesa-dev] [PATCH 3/3] i965/nir: use vectorization for non-scalar stages

[Ian Romanick]

On 10/18/2018 01:22 PM, Jason Ekstrand wrote:
> On Thu, Oct 18, 2018 at 3:11 PM Ian Romanick <idr at freedesktop.org
> <mailto:idr at freedesktop.org>> wrote:
> 
>     On 10/17/2018 11:33 AM, Jason Ekstrand wrote:
>     > From: Connor Abbott <cwabbott0 at gmail.com <mailto:cwabbott0 at gmail.com>>
>     >
>     > Shader-db results on Haswell:
>     >
>     >     total instructions in shared programs: 2180337 -> 2154080 (-1.20%)
>     >     instructions in affected programs: 959766 -> 933509 (-2.74%)
>     >     helped: 5653
>     >     HURT: 2560
>     >
>     >     total cycles in shared programs: 12339326 -> 12307102 (-0.26%)
>     >     cycles in affected programs: 6102794 -> 6070570 (-0.53%)
>     >     helped: 3838
>     >     HURT: 4868
> 
>     Here's the results I got with these 3 patches on 322a919a41f:
> 
>     total instructions in shared programs: 13674046 -> 13643001 (-0.23%)
>     instructions in affected programs: 1248672 -> 1217627 (-2.49%)
>     helped: 7168
>     HURT: 2841
>     helped stats (abs) min: 1 max: 39 x̄: 5.40 x̃: 3
>     helped stats (rel) min: 0.21% max: 33.33% x̄: 4.55% x̃: 3.54%
>     HURT stats (abs)   min: 1 max: 21 x̄: 2.71 x̃: 3
>     HURT stats (rel)   min: 0.19% max: 22.73% x̄: 3.86% x̃: 3.53%
>     95% mean confidence interval for instructions value: -3.23 -2.97
>     95% mean confidence interval for instructions %-change: -2.28% -2.05%
>     Instructions are helped.
> 
>     total cycles in shared programs: 373694400 -> 373745788 (0.01%)
>     cycles in affected programs: 23171532 -> 23222920 (0.22%)
>     helped: 4890
>     HURT: 5632
>     helped stats (abs) min: 2 max: 1268 x̄: 52.04 x̃: 34
>     helped stats (rel) min: 0.04% max: 45.71% x̄: 7.43% x̃: 4.64%
>     HURT stats (abs)   min: 2 max: 6042 x̄: 54.30 x̃: 32
>     HURT stats (rel)   min: 0.05% max: 60.66% x̄: 8.19% x̃: 6.21%
>     95% mean confidence interval for cycles value: 1.30 8.47
>     95% mean confidence interval for cycles %-change: 0.73% 1.14%
>     Cycles are HURT.
> 
>     total spills in shared programs: 82569 -> 82572 (<.01%)
>     spills in affected programs: 70 -> 73 (4.29%)
>     helped: 0
>     HURT: 3
> 
>     total fills in shared programs: 93445 -> 93449 (<.01%)
>     fills in affected programs: 71 -> 75 (5.63%)
>     helped: 0
>     HURT: 4
> 
>     This is pretty different from your result... and not good. :(  What SHA
>     of master were you on?
> 
> 
> For one thing, I scrubbed all the non-vec4 programs from the results
> because this doesn't affect FS.  I'm not sure what master; something
> from the last two days; I just rebased.  Maybe you have a newer shader-db?

I doubt my shader-db is newer.  The last time I updated was when you
added a bunch of shaders. :)  Scrubbing FS programs should only affect
the values shown in "total XXX in shader programs", right?  Or did you
do something other than

./report.py <(grep -v SIMD before.txt) <(grep -v SIMD after.txt)

When I do that, I get 'total ...' numbers a bit closer to, but still
larger than, yours.

Looking at the actual data, the shaders most hurt for cycles are all
shaders that have been in shader-db for years... lots of Unigine and
L4D2. :(  The spills / fills hurt are all TES in Tomb Raider.

>     > Most of the hurt programs seem to be because we generate extra
>     MOV's due
>     > to vectorizing things. For example, in
>     > shaders/non-free/steam/anomaly-2/158.shader_test, this:
>     >
>     > add(8)          g116<1>.xyF     g12<4,4,1>.xyyyF g1.4<0,4,1>.xyyyF
>     { align16 NoDDClr 1Q };
>     > add(8)          g117<1>.xyF     g12<4,4,1>.xyyyF g1.4<0,4,1>.zwwwF
>     { align16 NoDDClr 1Q };
>     > add(8)          g116<1>.zwF     g12<4,4,1>.xxxyF
>     -g1.4<0,4,1>.xxxyF { align16 NoDDChk 1Q };
>     > add(8)          g117<1>.zwF     g12<4,4,1>.xxxyF
>     -g1.4<0,4,1>.zzzwF { align16 NoDDChk 1Q };
>     >
>     > Turns into this:
>     >
>     > add(8)          g13<1>F         g12<4,4,1>.xyxyF g1.4<0,4,1>F   {
>     align16 1Q };
>     > add(8)          g14<1>F         g12<4,4,1>.xyxyF -g1.4<0,4,1>F  {
>     align16 1Q };
>     > mov(8)          g116<1>.xyD     g13<4,4,1>.xyyyD                {
>     align16 NoDDClr 1Q };
>     > mov(8)          g117<1>.xyD     g13<4,4,1>.zwwwD                {
>     align16 NoDDClr 1Q };
>     > mov(8)          g116<1>.zwD     g14<4,4,1>.xxxyD                {
>     align16 NoDDChk 1Q };
>     > mov(8)          g117<1>.zwD     g14<4,4,1>.zzzwD                {
>     align16 NoDDChk 1Q };
>     >
>     > So we eliminated two add's, but then had to introduce four mov's to
>     > transpose the result.  Some of the hurt is because vectorization
>     is a bit
>     > over-aggressive and we vectorize something when we should have left it
>     > as a scalar and CSEd it.  Unfortunately, this is all really tricky
>     to do
>     > as it involves the interactions between many different components.
>     > ---
>     >  src/intel/compiler/brw_nir.c | 6 ++++++
>     >  1 file changed, 6 insertions(+)
>     >
>     > diff --git a/src/intel/compiler/brw_nir.c
>     b/src/intel/compiler/brw_nir.c
>     > index 297845b89b7..564fd004a94 100644
>     > --- a/src/intel/compiler/brw_nir.c
>     > +++ b/src/intel/compiler/brw_nir.c
>     > @@ -568,6 +568,12 @@ brw_nir_optimize(nir_shader *nir, const
>     struct brw_compiler *compiler,
>     >        OPT(nir_copy_prop);
>     >        OPT(nir_opt_dce);
>     >        OPT(nir_opt_cse);
>     > +
>     > +      if (!is_scalar) {
>     > +         OPT(nir_opt_vectorize);
>     > +         OPT(nir_copy_prop);
>     > +      }
>     > +
>     >        OPT(nir_opt_peephole_select, 0);
>     >        OPT(nir_opt_intrinsics);
>     >        OPT(nir_opt_algebraic);
>     >
>