[Mesa-dev] [RFC 0/7] nir, i965/fs: Lower indirect local variables to scratch

[Jason Ekstrand]

On Dec 5, 2016 12:14 PM, "Connor Abbott" <cwabbott0 at gmail.com> wrote:

I'm a little worried about this since it seems like the
load/store_scratch intrinsics are basically doing the same thing as
registers were originally intended to do. Either we should use the
existing register lowering, and make it conditional on the size like
you've done here, or we should just gut larger-than-vec4 registers
entirely and go with this instead. TBH, I'm kinda leaning towards the
latter, since I know Rob has expressed some interest in using
something like this instead of registers, and it seems like nobody
really wants the ability to indirectly address stuff inside, say, an
add instruction anyways.


The vec4 backend does use indirects on registers today.  Another option in
this series would be to put the heuristic in lower_indirect_derefs instead
and let the larger indirected things turn into registers and do it that
way.  But I do like having separate instructions rather than those weird
indirect sources.

On Mon, Dec 5, 2016 at 2:59 PM, Jason Ekstrand <jason at jlekstrand.net> wrote:
> This little series implements lowering of indirectly accessed local
> variables larger than some threshold (8 floats?) to scratch space.  This
> improves the performance of the CSDof synmark test by about 45% because it
> uses a large temporary array which we lower to if-ladders and then to
piles
> of scratch.
>
> The approach I've taken here is to add a new set of NIR intrinsics for
> reading and writing scratch.  It's treated like any other form of IO with
a
> new nir_lower_vars_to_scratch pass that lowers everything over a given
size
> threshold to scratch space.  Why do this in NIR?  The primary reason is
> that this lets us lower to scratch *before* we do
nir_lower_indirect_derefs
> so we can still use registers for small indirects where an if-ladder is
> more efficient than scratch space.  Also, after gaving it a try, I really
> liked how those intrinsics turned out.
>
> This series is marked RFC because it's still a bit sketchy at the moment.
> There are a few things that would need to be finished before it's ready
for
> landing:
>
>  1) I should probably run it through piglit.
>  2) The back-end portion doesn't yet handle doubles
>  3) We should use send-from-GRF for non-spill direct scratch reads/writes.
>     Right now, it's still using MRFs which isn't great.
>
> If people like where this series is going, I can probably find some time
to
> polish it to the point of mergeable.
>
> Jason Ekstrand (6):
>   nir: Add load/store_scratch intrinsics
>   nir: Add a pass for selectively lowering variables to scratch space
>   i965/fs: Add a CHANNEL_IDS opcode
>   i965/fs: Add DWord scattered read/write opcodes
>   i965/fs: Implement the new nir_scratch_load/store opcodes
>   i965: Lower large local arrays to scratch
>
> Timothy Arceri (1):
>   i965: use nir_lower_indirect_derefs() for GLSL
>
>  src/compiler/Makefile.sources                     |   1 +
>  src/compiler/nir/nir.h                            |   8 +-
>  src/compiler/nir/nir_clone.c                      |   1 +
>  src/compiler/nir/nir_intrinsics.h                 |   6 +-
>  src/compiler/nir/nir_lower_scratch.c              | 258
++++++++++++++++++++++
>  src/intel/vulkan/anv_pipeline.c                   |  10 -
>  src/mesa/drivers/dri/i965/brw_defines.h           |  10 +
>  src/mesa/drivers/dri/i965/brw_fs.cpp              | 113 ++++++++++
>  src/mesa/drivers/dri/i965/brw_fs.h                |   6 +
>  src/mesa/drivers/dri/i965/brw_fs_cse.cpp          |   1 +
>  src/mesa/drivers/dri/i965/brw_fs_generator.cpp    | 170 ++++++++++++++
>  src/mesa/drivers/dri/i965/brw_fs_nir.cpp          |  42 +++-
>  src/mesa/drivers/dri/i965/brw_fs_reg_allocate.cpp |   4 +-
>  src/mesa/drivers/dri/i965/brw_link.cpp            |  13 --
>  src/mesa/drivers/dri/i965/brw_nir.c               |  13 ++
>  src/mesa/drivers/dri/i965/brw_shader.cpp          |  12 +
>  16 files changed, 631 insertions(+), 37 deletions(-)
>  create mode 100644 src/compiler/nir/nir_lower_scratch.c
>
> --
> 2.5.0.400.gff86faf
>
> _______________________________________________
> mesa-dev mailing list
> mesa-dev at lists.freedesktop.org
> https://lists.freedesktop.org/mailman/listinfo/mesa-dev
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <https://lists.freedesktop.org/archives/mesa-dev/attachments/20161205/cdace495/attachment.html>