[Mesa-dev] [PATCH v2 4/9] nir/deref: Add helpers for getting offsets

[Jason Ekstrand]

On Mon, Jul 2, 2018 at 11:10 AM, Kenneth Graunke <kenneth at whitecape.org>
wrote:

> On Friday, June 29, 2018 5:13:52 PM PDT Jason Ekstrand wrote:
> > These are very similar to the related function in nir_lower_io except
> > that they don't handle per-vertex or packed things (that could be added,
> > in theory) and they take a more detailed size/align function pointer.
> > One day, we should consider switching nir_lower_io over to using the
> > more detailed size/align functions and then we could make it use these
> > helpers instead of having its own.
> > ---
> >  src/compiler/nir/nir_deref.c | 91 ++++++++++++++++++++++++++++++++++++
> >  src/compiler/nir/nir_deref.h |  6 +++
> >  2 files changed, 97 insertions(+)
> >
> > diff --git a/src/compiler/nir/nir_deref.c b/src/compiler/nir/nir_deref.c
> > index 22ecde4ecca..94f91df5a0f 100644
> > --- a/src/compiler/nir/nir_deref.c
> > +++ b/src/compiler/nir/nir_deref.c
> > @@ -120,6 +120,97 @@ nir_deref_instr_has_indirect(nir_deref_instr
> *instr)
> >     return false;
> >  }
> >
> > +static unsigned
> > +type_get_array_stride(const struct glsl_type *elem_type,
> > +                      glsl_type_size_align_func size_align)
> > +{
> > +   unsigned elem_size, elem_align;
> > +   glsl_get_natural_size_align_bytes(elem_type, &elem_size,
> &elem_align);
> > +   return ALIGN_POT(elem_size, elem_align);
> > +}
> > +
> > +static unsigned
> > +struct_type_get_field_offset(const struct glsl_type *struct_type,
> > +                             glsl_type_size_align_func size_align,
> > +                             unsigned field_idx)
> > +{
> > +   assert(glsl_type_is_struct(struct_type));
> > +   unsigned offset = 0;
> > +   for (unsigned i = 0; i <= field_idx; i++) {
> > +      unsigned elem_size, elem_align;
> > +      glsl_get_natural_size_align_bytes(glsl_get_struct_field(struct_type,
> i),
> > +                                        &elem_size, &elem_align);
> > +      offset = ALIGN_POT(offset, elem_align);
> > +      if (i < field_idx)
> > +         offset += elem_size;
> > +   }
> > +   return offset;
> > +}
> > +
> > +unsigned
> > +nir_deref_instr_get_const_offset(nir_deref_instr *deref,
> > +                                 glsl_type_size_align_func size_align)
> > +{
> > +   nir_deref_path path;
> > +   nir_deref_path_init(&path, deref, NULL);
> > +
> > +   assert(path.path[0]->deref_type == nir_deref_type_var);
> > +   nir_deref_instr **p = &path.path[1];
> > +
> > +   unsigned offset = 0;
> > +   for (; *p; p++) {
>
> Personally, I'd just write
>
>    for (nir_deref_instr **p = &path.path[1]; *p; p++) {
>
> since you don't need it after the loop.
>

Good call.  Done.  The only reason I wrote it the way I did was because the
code I copied it from did it that way.  I think there is a good reason
there but not here.

--Jason


> > +      if ((*p)->deref_type == nir_deref_type_array) {
> > +         offset += nir_src_as_const_value((*p)->arr.index)->u32[0] *
> > +                   type_get_array_stride((*p)->type, size_align);
> > +      } else if ((*p)->deref_type == nir_deref_type_struct) {
> > +         /* p starts at path[1], so this is safe */
> > +         nir_deref_instr *parent = *(p - 1);
> > +         offset += struct_type_get_field_offset(parent->type,
> size_align,
> > +                                                (*p)->strct.index);
> > +      } else {
> > +         unreachable("Unsupported deref type");
> > +      }
> > +   }
> > +
> > +   nir_deref_path_finish(&path);
> > +
> > +   return offset;
> > +}
> > +
> > +nir_ssa_def *
> > +nir_build_deref_offset(nir_builder *b, nir_deref_instr *deref,
> > +                       glsl_type_size_align_func size_align)
> > +{
> > +   nir_deref_path path;
> > +   nir_deref_path_init(&path, deref, NULL);
> > +
> > +   assert(path.path[0]->deref_type == nir_deref_type_var);
> > +   nir_deref_instr **p = &path.path[1];
> > +
> > +   nir_ssa_def *offset = nir_imm_int(b, 0);
> > +   for (; *p; p++) {
>
> Ditto here.
>
> > +      if ((*p)->deref_type == nir_deref_type_array) {
> > +         nir_ssa_def *index = nir_ssa_for_src(b, (*p)->arr.index, 1);
> > +         nir_ssa_def *stride =
> > +            nir_imm_int(b, type_get_array_stride((*p)->type,
> size_align));
> > +         offset = nir_iadd(b, offset, nir_imul(b, index, stride));
> > +      } else if ((*p)->deref_type == nir_deref_type_struct) {
> > +         /* p starts at path[1], so this is safe */
> > +         nir_deref_instr *parent = *(p - 1);
> > +         unsigned field_offset =
> > +            struct_type_get_field_offset(parent->type, size_align,
> > +                                         (*p)->strct.index);
> > +         nir_iadd(b, offset, nir_imm_int(b, field_offset));
> > +      } else {
> > +         unreachable("Unsupported deref type");
> > +      }
> > +   }
> > +
> > +   nir_deref_path_finish(&path);
> > +
> > +   return offset;
> > +}
> > +
> >  bool
> >  nir_remove_dead_derefs_impl(nir_function_impl *impl)
> >  {
> > diff --git a/src/compiler/nir/nir_deref.h b/src/compiler/nir/nir_deref.h
> > index 0980bae7215..6f4141aaf82 100644
> > --- a/src/compiler/nir/nir_deref.h
> > +++ b/src/compiler/nir/nir_deref.h
> > @@ -48,6 +48,12 @@ void nir_deref_path_init(nir_deref_path *path,
> >                           nir_deref_instr *deref, void *mem_ctx);
> >  void nir_deref_path_finish(nir_deref_path *path);
> >
> > +unsigned nir_deref_instr_get_const_offset(nir_deref_instr *deref,
> > +                                          glsl_type_size_align_func
> size_align);
> > +
> > +nir_ssa_def *nir_build_deref_offset(nir_builder *b, nir_deref_instr
> *deref,
> > +                                    glsl_type_size_align_func
> size_align);
> > +
> >  #ifdef __cplusplus
> >  } /* extern "C" */
> >  #endif
> >
>
>
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