[Mesa-stable] [PATCH] glsl: change ast_type_qualifier bitset size to work around GCC 5.4 bug

[Ian Romanick]

On 05/08/2018 07:43 AM, Brian Paul wrote:
> Change the size of the bitset from 128 bits to 96.  This works around an
> apparent GCC 5.4 bug in which bad SSE code is generated, leading to a
> crash in ast_type_qualifier::validate_in_qualifier() (ast_type.cpp:654).

Is there a difference in the code quality on newer versions of GCC?
This work-around seems fine, but I wonder if it should be restricted to
the affected GCC versions.

> This can be repro'd with the Piglit test tests/spec/glsl-1.50/execution/
> varying-struct-basic-gs-fs.shader_test
> 
> Bugzilla:https://bugs.freedesktop.org/show_bug.cgi?id=105497
> Cc: mesa-stable at lists.freedesktop.org
> ---
>  src/compiler/glsl/ast.h | 8 +++++++-
>  1 file changed, 7 insertions(+), 1 deletion(-)
> 
> diff --git a/src/compiler/glsl/ast.h b/src/compiler/glsl/ast.h
> index a1ec0d5..9b88ff5 100644
> --- a/src/compiler/glsl/ast.h
> +++ b/src/compiler/glsl/ast.h
> @@ -474,7 +474,13 @@ enum {
>  
>  struct ast_type_qualifier {
>     DECLARE_RALLOC_CXX_OPERATORS(ast_type_qualifier);
> -   DECLARE_BITSET_T(bitset_t, 128);
> +   /* Note: this bitset needs to have at least as many bits as the 'q'
> +    * struct has flags, below.  Previously, the size was 128 instead of 96.
> +    * But an apparent bug in GCC 5.4.0 causes bad SSE code generation
> +    * elsewhere, leading to a crash.  96 bits works around the issue.
> +    * See https://bugs.freedesktop.org/show_bug.cgi?id=105497
> +    */
> +   DECLARE_BITSET_T(bitset_t, 96);
>  
>     union flags {
>        struct {