[Mesa-dev] [PATCH 0/6] i965/fs: Integer multiplication improvements

[Jason Ekstrand]

On Fri, May 15, 2015 at 2:02 PM, Matt Turner <mattst88 at gmail.com> wrote:
> This series reworks how we do integer multiplication in the i965/fs
> backend and significantly improves code generation for Broadwell's
> scalar vertex shaders with NIR by allowing constant propagation into
> the MUL instruction (wow that code was stupid, and it still kind of
> is!).
>
> Before this series, Jason said enabling NIR for scalar vertex shaders
> had this result:
>
> total instructions in shared programs: 2724483 -> 2711790 (-0.47%)
> instructions in affected programs:     1860859 -> 1848166 (-0.68%)
> helped:                                4387
> HURT:                                  4758
>
> After this series, the results are:
>
> Broadwell, vertex shaders only, with and without NIR:
> total instructions in shared programs: 2742062 -> 2681339 (-2.21%)
> instructions in affected programs:     1514770 -> 1454047 (-4.01%)
> helped:                                5813
> HURT:                                  1120
>
> Along the way, I move when we split integer multiplication into multiple
> instructions (on Gen < 8), implement SIMD16 support, and reimplement
> integer multiplication on Gen < 8 without using the accumulator.
>
> Patches 3 and 4, add SIMD16 support (for Haswell only, since pre-Gen7
> already works, and IVB/BYT have a bug that prevents it from working).
> I don't particularly care if those patches go in separately, or if 6/6
> is squashed with 4/6, but I think they are instructive -- I'll follow
> up with a piglit test that demonstrates that settings the wrong quarter
> control indeed generates incorrect results.

I've got a comment on 6 that I think needs some fixing but 1-5 are

Reviewed-by: Jason Ekstrand <jason.ekstrand at intel.com>

Please leave 4 and 6 unsquashed.
--Jason

> I did not touch the imul_high opcode, though it could be lowered in a
> similar way (and probably in 3 instructions using the same tricks in 6/6).
> That would be a nice follow-on project, and it would mean we'd never see
> a MACH instruction during optimizations.
>
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