[Mesa-dev] [PATCH 08/15] glsl: Switch ast_type_qualifier to a 128-bit bitset.

[Roland Scheidegger]

Am 25.02.2018 um 21:12 schrieb Francisco Jerez:
> Roland Scheidegger <sroland at vmware.com> writes:
> 
>> Am 25.02.2018 um 03:35 schrieb Francisco Jerez:
>>> Roland Scheidegger <sroland at vmware.com> writes:
>>>
>>>> This seems to have broken compilation with some gcc versions (with scons
>>>> build):
>>>>
>>>> In file included from src/compiler/glsl/ast_array_index.cpp:24:0:
>>>> src/compiler/glsl/ast.h:648:16: error: member
>>>> ‘ast_type_qualifier::bitset_t ast_type_qualifier::flags::i’ with
>>>> constructor not allowed in union
>>>>        bitset_t i;
>>>>                 ^
>>>
>>> Oops...  And the only reason bitset_t has a default constructor was...
>>> to avoid using another C++11 feature (defaulted member functions).
>>> Does the attached patch fix the build failure for you?  The cleaner
>>> alternative would be to define the default constructor of the bitset
>>> object like 'T() = default', but that would imply dropping support for
>>> GCC 4.2-4.3 which don't implement the feature...
>>
>> FWIW the compile error was happening with gcc 4.8 - I didn't see it with
>> gcc 5.4.
>> (I don't think at vmware we'd care about anything older than gcc 4.4 at
>> least but last time someone wanted to bump gcc requirements there were
>> still people requiring gcc 4.2.)
>>
>> The patch compiles albeit there's about two dozen warnings like the
>> following:
>> glsl/ast_type.cpp: In member function 'bool
>> ast_fully_specified_type::has_qualifiers(_mesa_glsl_parse_state*) const':
>> glsl/ast_type.cpp:50:67: warning: ISO C++ says that these are ambiguous,
>> even though the worst conversion for the first is better than the worst
>> conversion for the second: [enabled by default]
>>     return (this->qualifier.flags.i & ~subroutine_only.flags.i) != 0;
>>                                                                    ^
>> In file included from glsl/ast.h:31:0,
>>                  from glsl/ast_type.cpp:24:
>> ../../src/util/bitset.h:181:7: note: candidate 1: bool operator!=(const
>> ast_type_qualifier::bitset_t&, unsigned int)
>>        operator!=(const T &b, BITSET_WORD x)                     \
>>        ^
>> glsl/ast.h:477:4: note: in expansion of macro 'DECLARE_BITSET_T'
>>     DECLARE_BITSET_T(bitset_t, 128);
>>     ^
>> glsl/ast_type.cpp:50:67: note: candidate 2: operator!=(int, int) <built-in>
>>     return (this->qualifier.flags.i & ~subroutine_only.flags.i) != 0;
>>                                                                    ^
>> Roland
>>
> 
> Ah, yeah, that's because I didn't provide overloads for signed integer
> types, but it should be harmless since the two candidates have the same
> semantics, and should go away with a C++11-capable compiler.  I think
> the attached patch should shut the warnings on older compilers.

Yes, that compiles without warnings (with gcc 4.8)
Tested-by: Roland Scheidegger <sroland at vmware.com>


> 
>>
>>
>>>
>>>> src/compiler/glsl/ast.h:648:16: note: unrestricted unions only available
>>>> with -std=c++11 or -std=gnu++11
>>>> scons: *** [build/linux-x86_64-checked/compiler/glsl/ast_array_index.os]
>>>> Error 1
>>>> src/gallium/tests/unit/u_format_test.c: In function ‘main’:
>>>> src/gallium/tests/unit/u_format_test.c:649:44: warning: array subscript
>>>> is above array bounds [-Warray-bounds]
>>>>           unpacked[i][j] = test->unpacked[i][j][1];
>>>>                                             ^
>>>> In file included from src/compiler/glsl/ast_expr.cpp:24:0:
>>>> src/compiler/glsl/ast.h:648:16: error: member
>>>> ‘ast_type_qualifier::bitset_t ast_type_qualifier::flags::i’ with
>>>> constructor not allowed in union
>>>>        bitset_t i;
>>>>                 ^
>>>> src/compiler/glsl/ast.h:648:16: note: unrestricted unions only available
>>>> with -std=c++11 or -std=gnu++11
>>>>
>>>> Roland
>>>>
>>>> [...]
>>>
>