[Mesa-dev] [PATCH 1/2] nir: Add a function to determine if a source is dynamically uniform

[Francisco Jerez]

Jason Ekstrand <jason at jlekstrand.net> writes:

> On Oct 1, 2015 12:18 PM, "Matt Turner" <mattst88 at gmail.com> wrote:
>>
>> On Fri, Aug 7, 2015 at 9:31 AM, Neil Roberts <neil at linux.intel.com> wrote:
>> > Adds nir_src_is_dynamically_uniform which returns true if the source
>> > is known to be dynamically uniform. This will be used in a later patch
>> > to add a workaround for cases that only work with dynamically uniform
>> > sources. Note that the function is not definitive, it can return false
>> > negatives (but not false positives). Currently it only detects
>> > constants and uniform accesses. It could easily be extended to include
>> > more cases.
>> > ---
>> >  src/glsl/nir/nir.c | 29 +++++++++++++++++++++++++++++
>> >  src/glsl/nir/nir.h |  1 +
>> >  2 files changed, 30 insertions(+)
>> >
>> > diff --git a/src/glsl/nir/nir.c b/src/glsl/nir/nir.c
>> > index 78ff886..242f0b4 100644
>> > --- a/src/glsl/nir/nir.c
>> > +++ b/src/glsl/nir/nir.c
>> > @@ -1784,6 +1784,35 @@ nir_src_as_const_value(nir_src src)
>> >     return &load->value;
>> >  }
>> >
>> > +/**
>> > + * Returns true if the source is known to be dynamically uniform.
> Otherwise it
>> > + * returns false which means it may or may not be dynamically uniform
> but it
>> > + * can't be determined.
>> > + */
>> > +bool
>> > +nir_src_is_dynamically_uniform(nir_src src)
>> > +{
>> > +   if (!src.is_ssa)
>> > +      return false;
>> > +
>> > +   /* Constants are trivially dynamically uniform */
>> > +   if (src.ssa->parent_instr->type == nir_instr_type_load_const)
>> > +      return true;
>> > +
>> > +   /* As are uniform variables */
>> > +   if (src.ssa->parent_instr->type == nir_instr_type_intrinsic) {
>> > +      nir_intrinsic_instr *intr =
> nir_instr_as_intrinsic(src.ssa->parent_instr);
>> > +
>> > +      if (intr->intrinsic == nir_intrinsic_load_uniform)
>> > +         return true;
>> > +   }
>> > +
>> > +   /* XXX: this could have many more tests, such as when a sampler
> function is
>> > +    * called with dynamically uniform arguments.
>> > +    */
>> > +   return false;
>> > +}
>>
>> This functions seems correct as-is, so it gets a
>>
>> Reviewed-by: Matt Turner <mattst88 at gmail.com>
>>
>> On top of being useful for fixing the nonconst/nonuniform piglit
>> tests, knowing which values are uniform can allow better optimization
>> and knowing which branches are uniform would allow us to enable Single
>> Program Flow.
>>
>> Cc'ing Jason for a discussion about how we'd like to handle this kind
>> of information in NIR. Add a bool is_uniform or something to
>> nir_ssa_def and hook into the metadata system?
>
> That was more-or-less my plan. We should probably have a proper pass that
> handles things like phi nodes and ALU operations.
>

Heh, I hadn't noticed this series until now and happen to have started
to sketch such an analysis pass just this week, with a completely
unrelated purpose in mind (enable a restricted form of GCM for texturing
ops with implicit derivatives).  Any volunteers to write it (Neil?) or
shall I go ahead with it?

> --Jason
> _______________________________________________
> mesa-dev mailing list
> mesa-dev at lists.freedesktop.org
> http://lists.freedesktop.org/mailman/listinfo/mesa-dev
-------------- next part --------------
A non-text attachment was scrubbed...
Name: signature.asc
Type: application/pgp-signature
Size: 212 bytes
Desc: not available
URL: <http://lists.freedesktop.org/archives/mesa-dev/attachments/20151002/52c9d770/attachment-0001.sig>