[Pixman] [PATCH] Workaround bug in llvm-gcc

[Soeren Sandmann]

Andrea Canciani <ranma42 at gmail.com> writes:

> llvm-gcc (shipped in Apple XCode 4.1.1 as the default compiler or in
> the 2.9 release of LLVM) performs an invalid optimization which
> unifies the empty_region and the bad_region structures because they
> have the same content.
>
> A bug has been filed against Apple Developers Tool for this
> issue. This commit works around this bug by making one of the two
> structures volatile, so that it cannot be merged.

Is the bug report publicly readable?

>  static const box_type_t PREFIX (_empty_box_) = { 0, 0, 0, 0 };
>  static const region_data_type_t PREFIX (_empty_data_) = { 0, 0 };
> +#if defined (__llvm__) && !defined (__clang__)
> +static const volatile region_data_type_t PREFIX (_broken_data_) = { 0, 0 };
> +#else
>  static const region_data_type_t PREFIX (_broken_data_) = { 0, 0 };
> +#endif

It worries me a little that these #ifdefs will still trigger when Apple
fix their compiler. Can we detect it at configure time instead by
running something like this:

        typedef struct { int x, y; } blah_t;

        static const blah_t b1 = { 0, 0 };
        static const blah_t b2 = { 0, 0 };

        int
        main ()
        {
                if (&b1 == &b2)
                        return 1;
                else
                        return 0;
        }


Soren