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

[Kenneth Graunke]

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.

> +      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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