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

[Roland Scheidegger]

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



> 
>> 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
>>
>> [...]
>