[Mesa-dev] [PATCH] ac/nir: mark some texture intrinsics as convergent

[Ilia Mirkin]

txf supplies an lod, but tg4's is implicitly always 0.

On Thu, May 30, 2019 at 2:26 PM Bas Nieuwenhuizen
<bas at basnieuwenhuizen.nl> wrote:
>
> On Thu, May 30, 2019 at 6:50 PM Rhys Perry <pendingchaos02 at gmail.com> wrote:
> >
> > Otherwise LLVM can sink them and their texture coordinate calculations
> > into divergent branches.
> >
> > Cc: <mesa-stable at lists.freedesktop.org>
> > Signed-off-by: Rhys Perry <pendingchaos02 at gmail.com>
> > ---
> >  src/amd/common/ac_nir_to_llvm.c | 29 +++++++++++++++++++++++++++++
> >  1 file changed, 29 insertions(+)
> >
> > diff --git a/src/amd/common/ac_nir_to_llvm.c b/src/amd/common/ac_nir_to_llvm.c
> > index 265e3b636c4..d2dc617de36 100644
> > --- a/src/amd/common/ac_nir_to_llvm.c
> > +++ b/src/amd/common/ac_nir_to_llvm.c
> > @@ -1316,6 +1316,30 @@ static nir_deref_instr *get_tex_texture_deref(const nir_tex_instr *instr)
> >         return texture_deref_instr;
> >  }
> >
> > +static bool has_implicit_derivatives(const nir_tex_instr *instr)
> > +{
> > +       switch (instr->op) {
> > +       case nir_texop_txs:
> > +       case nir_texop_query_levels:
> > +       case nir_texop_texture_samples:
> > +       case nir_texop_samples_identical:
> > +               return false;
> > +       default:
> > +               break;
> > +       }
> > +       for (unsigned i = 0; i < instr->num_srcs; i++) {
> > +               switch (instr->src[i].src_type) {
> > +               case nir_tex_src_lod:
> > +               case nir_tex_src_ddx:
> > +               case nir_tex_src_ddy:
> > +                       return false;
> > +               default:
> > +                       break;
> > +               }
> > +       }
> > +       return true;
> > +}
>
> txf, tg4 and friends do not provide any of lod/ddx/ddy do they?
>
> > +
> >  static LLVMValueRef build_tex_intrinsic(struct ac_nir_context *ctx,
> >                                         const nir_tex_instr *instr,
> >                                         struct ac_image_args *args)
> > @@ -1394,6 +1418,11 @@ static LLVMValueRef build_tex_intrinsic(struct ac_nir_context *ctx,
> >         }
> >
> >         args->attributes = AC_FUNC_ATTR_READNONE;
> > +       /* Prevent texture instructions with implicit derivatives from being
> > +        * sinked into branches. */
> > +       if (has_implicit_derivatives(instr))
> > +               args->attributes |= AC_FUNC_ATTR_CONVERGENT;
> > +
> >         return ac_build_image_opcode(&ctx->ac, args);
> >  }
> >
> > --
> > 2.21.0
> >
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