On Tue, 2016-01-12 at 20:34 +1100, Timothy Arceri wrote:
> From Section 4.4.5 (Uniform and Shader Storage Block Layout
> Qualifiers) of the OpenGL 4.50 spec:
> 
>   "The align qualifier makes the start of each block member have a
>   minimum byte alignment.  It does not affect the internal layout
>   within each member, which will still follow the std140 or std430
>   rules. The specified alignment must be a power of 2, or a
>   compile-time error results.
> 
>   The actual alignment of a member will be the greater of the
>   specified align alignment and the standard (e.g., std140) base
>   alignment for the member's type. The actual offset of a member is
>   computed as follows: If offset was declared, start with that
>   offset, otherwise start with the next available offset. If the
>   resulting offset is not a multiple of the actual alignment,
>   increase it to the first offset that is a multiple of the actual
>   alignment. This results in the actual offset the member will have.
> 
>   When align is applied to an array, it affects only the start of
>   the array, not the array's internal stride. Both an offset and an
>   align qualifier can be specified on a declaration.
> 
>   The align qualifier, when used on a block, has the same effect as
>   qualifying each member with the same align value as declared on
>   the block, and gets the same compile-time results and errors as if
>   this had been done. As described in general earlier, an individual
>   member can specify its own align, which overrides the block-level
>   align, but just for that member.
> ---
>  src/glsl/ast_to_hir.cpp | 51
> ++++++++++++++++++++++++++++++++++++++++++++++---
>  1 file changed, 48 insertions(+), 3 deletions(-)
> 
> diff --git a/src/glsl/ast_to_hir.cpp b/src/glsl/ast_to_hir.cpp
> index f5da771..fd05fd7 100644
> --- a/src/glsl/ast_to_hir.cpp
> +++ b/src/glsl/ast_to_hir.cpp
> @@ -6212,7 +6212,8 @@
> ast_process_struct_or_iface_block_members(exec_list *instructions,
>                                            ir_variable_mode var_mode,
>                                            ast_type_qualifier
> *layout,
>                                            unsigned block_stream,
> -                                          unsigned expl_location)
> +                                          unsigned expl_location,
> +                                          unsigned expl_align)
>  {
>     unsigned decl_count = 0;
>     unsigned next_offset = 0;
> @@ -6466,6 +6467,34 @@
> ast_process_struct_or_iface_block_members(exec_list *instructions,
>              }
>           } else {
>              fields[i].offset = -1;
> +         }
> +
> +         if (qual->flags.q.explicit_align || expl_align != 0) {
> +            unsigned offset = fields[i].offset != -1 ?
> fields[i].offset :
> +               next_offset;
> +            if (align == 0 || size == 0) {
> +               _mesa_glsl_error(&loc, state, "align can only be used
> with "
> +                                "std430 and std140 layouts");
> +            } else if (qual->flags.q.explicit_align) {
> +               unsigned member_align;
> +               if (process_qualifier_constant(state, &loc, "align",
> +                                              qual->align,
> &member_align)) {
> +                  if (member_align == 0 ||

I have modified ubo-block-align-zero.vert piglit test to set the align
qualifier only to block members and tested with align = 0. The shader
compiles on NVIDIA proprietary driver.

According to the spec, the specified alignment must be a power of 2.
However align = 0 could have different interpretations (for example,
when applied to a block member, it would mean to ignore block's align
value). As I am not sure about this case...

Have you checked if align = 0 is invalid?

Sam

> +                      member_align & (member_align - 1)) {
> +                     _mesa_glsl_error(&loc, state, "align layout
> qualifier "
> +                                      "in not a power of 2");
> +                  } else {
> +                     fields[i].offset = glsl_align(offset,
> member_align);
> +                     next_offset = glsl_align(fields[i].offset +
> size, align);
> +                  }
> +               }
> +            } else {
> +               fields[i].offset = glsl_align(offset, expl_align);
> +               next_offset = glsl_align(fields[i].offset + size,
> align);
> +            }
> +         }
> +
> +         if (!qual->flags.q.explicit_offset) {
>              if (align != 0 && size != 0)
>                 next_offset = glsl_align(next_offset + size, align);
>           }
> @@ -6590,7 +6619,8 @@ ast_struct_specifier::hir(exec_list
> *instructions,
>                                                  ir_var_auto,
>                                                  layout,
>                                                  0, /* for interface
> only */
> -                                                expl_location);
> +                                                expl_location,
> +                                                0 /* for interface
> only */);
>  
>     validate_identifier(this->name, loc, state);
>  
> @@ -6771,6 +6801,20 @@ ast_interface_block::hir(exec_list
> *instructions,
>        }
>     }
>  
> +   unsigned expl_align = 0;
> +   if (layout.flags.q.explicit_align) {
> +      if (!process_qualifier_constant(state, &loc, "align",
> +                                      layout.align, &expl_align)) {
> +         return NULL;
> +      } else {
> +         if (expl_align == 0 || expl_align & (expl_align - 1)) {

Same as before.

Sam

> +            _mesa_glsl_error(&loc, state, "align layout qualifier in
> not a "
> +                             "power of 2.");
> +            return NULL;
> +         }
> +      }
> +   }
> +
>     unsigned int num_variables =
>        ast_process_struct_or_iface_block_members(&declared_variables,
>                                                  state,
> @@ -6782,7 +6826,8 @@ ast_interface_block::hir(exec_list
> *instructions,
>                                                  var_mode,
>                                                  &this->layout,
>                                                  qual_stream,
> -                                                expl_location);
> +                                                expl_location,
> +                                                expl_align);
>  
>     state->struct_specifier_depth--;
>  

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