[Mesa-dev] [PATCH 0/9] glsl: cleanup and fix handling of unnamed struct types

[Ian Romanick]

On 05/15/2017 02:27 AM, Nicolai Hähnle wrote:
> Hi all,
> 
> This series aims to simplify how we handle unnamed struct types and fix some
> bugs on the way. Some of the patches should be uncontroversial, and all of
> them align with my understanding of the GLSL spec, but the spec isn't
> exactly explicit, so...
> 
> At a high level, the series changes two things:
> 
> 1) Unnamed structs can never match named structs during linking.
> 
> 2) Unnamed structs are considered the same type if they have the same
> content. They will literally use the same glsl_type instance.
> 
> The second point causes a deviation from the behavior of C/C++, in that the
> following code snippet now compiles (and does the reasonable thing):
> 
>   struct { float a; } s1;
>   struct { float a; } s2;
> 
>   s2 = s1;

I'll have to do some archaeology, but I believe this is what we used to
do.  I believe that we changed it because we were required to do so.

Does this fix some app, or is it just to simplify the code?

> The justification is basically that the GLSL spec says (when it comes to
> linking, in Section 4.2) that
> 
>    "Structures must have the same name, sequence of type names, and
>     type definitions, and member names to be considered the same type."
> 
> And since people generally seem to read that as mandating that globals of
> unnamed struct types should match if they're structurally the same, and the
> GLSL spec otherwise says nothing (as far as I can tell) about when struct
> types are equal, the cleanest thing is to just say that _in general_ (not
> just for linking) struct types are the same if and only if they have the
> same name and the same fields; where "same name" can mean that they both
> have no name.
> 
> Please contemplate and review! :)
> Thanks,
> Nicolai
> --
>  src/compiler/glsl/ast.h                   |  1 +
>  src/compiler/glsl/ast_to_hir.cpp          | 17 ++---
>  src/compiler/glsl/glsl_parser_extras.cpp  | 17 +++--
>  src/compiler/glsl/link_varyings.cpp       | 41 +++---------
>  src/compiler/glsl/linker.cpp              | 47 +++++---------
>  src/compiler/glsl/lower_ubo_reference.cpp |  2 +-
>  src/compiler/glsl_types.cpp               | 69 +++++++++------------
>  src/compiler/glsl_types.h                 | 11 ++--
>  8 files changed, 80 insertions(+), 125 deletions(-)
> 
> _______________________________________________
> mesa-dev mailing list
> mesa-dev at lists.freedesktop.org
> https://lists.freedesktop.org/mailman/listinfo/mesa-dev
>