[Mesa-dev] [PATCH] i965/cs: Don't use a thread channel ID for small local sizes

[Jordan Justen]

On 2016-10-19 13:47:35, Ian Romanick wrote:
> On 10/19/2016 12:45 PM, Jordan Justen wrote:
> > When the local group size is 8 or less, we will execute the program at
> > most 1 time. Therefore, the local channel ID will always be 0. By
> > using a constant 0 in this case we can prevent using push constant
> > data.
> > 
> > This is not expected to be common a occurance in real applications,
> > but it has been seen in tests.
> > 
> > We could extend this optimization to 16 and 32 for SIMD16 and SIMD32,
> > but it gets a bit more complicated, because this optimization is
> > currently being done early on, before we have decided the SIMD size.
> > 
> > Signed-off-by: Jordan Justen <jordan.l.justen at intel.com>
> > ---
> >  src/mesa/drivers/dri/i965/brw_nir_intrinsics.c | 13 +++++++++++--
> >  1 file changed, 11 insertions(+), 2 deletions(-)
> > 
> > diff --git a/src/mesa/drivers/dri/i965/brw_nir_intrinsics.c b/src/mesa/drivers/dri/i965/brw_nir_intrinsics.c
> > index 9ae161f..60f302e 100644
> > --- a/src/mesa/drivers/dri/i965/brw_nir_intrinsics.c
> > +++ b/src/mesa/drivers/dri/i965/brw_nir_intrinsics.c
> > @@ -39,12 +39,21 @@ struct lower_intrinsics_state {
> >  static nir_ssa_def *
> >  read_thread_local_id(struct lower_intrinsics_state *state)
> >  {
> > +   nir_builder *b = &state->builder;
> > +   nir_shader *nir = state->nir;
> > +   const unsigned *sizes = nir->info.cs.local_size;
> > +   const group_size = sizes[0] * sizes[1] * sizes[2];
>            ^
>             Isn't this missing a type?  Did you test this? :)

Yikes. Yeah, I sent it through jenkins. I guess it defaults to int in
this case:

  CC       brw_nir_intrinsics.lo
brw_nir_intrinsics.c: In function ‘read_thread_local_id’:
brw_nir_intrinsics.c:45:10: warning: type defaults to ‘int’ in declaration of ‘group_size’ [-Wimplicit-int]
    const group_size = sizes[0] * sizes[1] * sizes[2];
          ^

I'll add unsigned.

-Jordan

> > +
> > +   /* Some programs have local_size dimensions so small that the thread local
> > +    * ID will always be 0.
> > +    */
> > +   if (group_size <= 8)
> > +      return nir_imm_int(b, 0);
> > +
> >     assert(state->cs_prog_data->thread_local_id_index >= 0);
> >     state->cs_thread_id_used = true;
> >     const int id_index = state->cs_prog_data->thread_local_id_index;
> >  
> > -   nir_builder *b = &state->builder;
> > -   nir_shader *nir = state->nir;
> >     nir_intrinsic_instr *load =
> >        nir_intrinsic_instr_create(nir, nir_intrinsic_load_uniform);
> >     load->num_components = 1;
> > 
>