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

[Ian Romanick]

On 05/08/2018 12:13 PM, Ian Romanick wrote:
> 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.

Now that I've read the rest of the thread,

Reviewed-by: Ian Romanick <ian.d.romanick at intel.com>

>> 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 {
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