[Mesa-dev] [PATCH 0/3] Fix racy full-vector writes for v[i].x

[Jason Ekstrand]

On Mon, Nov 9, 2015 at 3:52 PM, Ian Romanick <idr at freedesktop.org> wrote:
> On 11/04/2015 03:55 PM, Jason Ekstrand wrote:
>> Here's some shader-db  numbers:
>>
>> total instructions in shared programs: 6236146 -> 6255385 (0.31%)
>> instructions in affected programs:     203629 -> 222868 (9.45%)
>> helped:                                118
>> HURT:                                  1989
>> GAINED:                                18
>> LOST:                                  0
>
> I recall from off-line discussions that many (almost all?) of the really
> hurt shaders were vertex shaders that we no longer getting benefit from
> the vectorizer pass.  How hard would be it be to modify the lowering
> pass to have an option to only lower SSBOs and other memories that
> actually need the early lowering?  We could then lower those early, do
> the vectorizing, the lower the others late (as we do now).
>
> I know we really want a NIR vectorizer, but I think that's a bigger
> project than we want to tackle right now.  If we think this stop-gap
> could be implemented quickly enough, maybe we should do that for now
> instead.

I believe this has all been fixed in v2.

>> We should probably look into that.
>>
>>
>> On Wed, Nov 4, 2015 at 3:33 PM, Kristian Høgsberg Kristensen
>> <krh at bitplanet.net> wrote:
>>> This little series fixes a problem where we lower
>>>
>>>   v[i] = s
>>>
>>> to
>>>
>>>   v = vector_insert(v, s, i)
>>>
>>> turning a component write into a full vector write. This used to be
>>> ok, since none of this was visible to other threads.  Now with SSBOs
>>> (and compute shader SLM and tesselation outputs) this rewrite is racy
>>> and we have to handle this different in case the vector is in globally
>>> visible storage.
>>>
>>> Kristian Høgsberg Kristensen (3):
>>>   glsl: Drop exec_list argument to lower_ubo_reference
>>>   glsl: Lower UBO and SSBO access in glsl linker
>>>   glsl: Use array deref for access to vector components
>>>
>>>  src/glsl/Makefile.sources                  |   1 +
>>>  src/glsl/ast_array_index.cpp               |   5 +-
>>>  src/glsl/ast_function.cpp                  |  24 ++-----
>>>  src/glsl/ast_to_hir.cpp                    |  43 ------------
>>>  src/glsl/ir_optimization.h                 |   3 +-
>>>  src/glsl/ir_validate.cpp                   |   7 +-
>>>  src/glsl/linker.cpp                        |  10 +++
>>>  src/glsl/lower_ubo_reference.cpp           |  18 ++++-
>>>  src/glsl/lower_vector_derefs.cpp           | 104 +++++++++++++++++++++++++++++
>>>  src/glsl/opt_dead_code_local.cpp           |   2 +
>>>  src/mesa/drivers/dri/i965/brw_link.cpp     |   2 -
>>>  src/mesa/drivers/dri/i965/brw_shader.cpp   |   2 +
>>>  src/mesa/main/mtypes.h                     |   2 +
>>>  src/mesa/state_tracker/st_extensions.c     |   1 +
>>>  src/mesa/state_tracker/st_glsl_to_tgsi.cpp |   1 -
>>>  15 files changed, 151 insertions(+), 74 deletions(-)
>>>  create mode 100644 src/glsl/lower_vector_derefs.cpp
>>>
>>> --
>>> 2.6.2
>>>
>>> _______________________________________________
>>> mesa-dev mailing list
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>