[Pixman] Pixman not building on MacOS X 10.11

[Matt Turner]

On Sun, Oct 11, 2015 at 10:34 AM, Andrea Canciani <ranma42 at gmail.com> wrote:
> On Sun, Oct 11, 2015 at 5:30 AM, Siarhei Siamashka
> <siarhei.siamashka at gmail.com> wrote:
>>
>> On Sun, 11 Oct 2015 04:53:08 +0300
>> Siarhei Siamashka <siarhei.siamashka at gmail.com> wrote:
>>
>> > On Sat, 10 Oct 2015 16:03:53 -0700
>> > Jeremy Huddleston Sequoia <jeremyhu at freedesktop.org> wrote:
>> >
>> > > > On Oct 10, 2015, at 13:48, Andrea Canciani <ranma42 at gmail.com>
>> > > > wrote:
>> > > > The attached hack gets the code to compile on modern clang, but I
>> > > > believe first of all we should improve the configure.ac detection
>> > > > code
>> > > > so that pixman can actually build both on old and on new clang
>> > > > versions (possibly with mmx disabled, if the asm constraints we need
>> > > > are not implemented).
>> >
>> > This workaround looks reasonable to me. We should probably just drop
>> > the whole "ifdef __OPTIMIZE__" part in
>> >
>> > http://cgit.freedesktop.org/pixman/tree/pixman/pixman-mmx.c?id=pixman-0.32.8#n92
>> >
>> > I don't quite like the fact that this way of returning results from
>> > a macro is a GNU C specific extension. But as you said, the configure
>> > test can be updated to better match the code and also check if the
>> > compiler supports this particular construct.
>> >
>> > Could you please submit the final variant of your patch in a
>> > "git format-patch" format with a commit message and your
>> > Signed-off-by tag?
>>
>> After looking at this issue a bit more, I realized that we are
>> about to add a second layer of workarounds on top of the existing
>> old workarounds :-)
>
>
> The attached patch should fix the issue with only minor changes.
> It keeps the workarounds :( but somewhat it simplifies them :)
> I followed your suggestion of checking&using block expressions.
> Given that the _mm_shuffle_pi16() function is always used in a "return"
> statement, if needed we could avoid the usage of block expressions by
> defining a macro "_return_mm_shuffle_pi16()" (which would return the result
> of the operation instead of making it available as an expression) both for
> the xmmintrin branch and for the hand-coded one.
>
>> The original problem is that certain compilers (just GCC?) did not
>> support some intrinsics when compiling MMX code (_mm_movemask_pi8,
>> _mm_mulhi_pu16, _mm_shuffle_pi16) and we got the following code:
>>
>> http://cgit.freedesktop.org/pixman/tree/pixman/pixman-mmx.c?id=pixman-0.32.8#n66
>>
>> In fact, these instructions were not available as part of the original
>> MMX, but only got introduced later with AMD Extended 3DNow! and Intel
>> SSE1. This is mentioned in the commit messages:
>>
>> http://cgit.freedesktop.org/pixman/commit/?id=84221f4c1687b8ea14e9cbdc78b2ba7258e62c9e
>>
>> http://cgit.freedesktop.org/pixman/commit/?id=14208344964f341a7b4a704b05cf4804c23792e9
>>
>> These extra instructions are unofficially known as MMX2. But GCC does
>> not have a separate option for "-mmmx2". Instead the GCC manual says
>> that these intrinsics are available when either "-msse" or a
>> combination of "-m3dnow -march=athlon" is used:
>>
>> https://gcc.gnu.org/onlinedocs/gcc-5.2.0/gcc/x86-Built-in-Functions.html#x86-Built-in-Functions
>>
>>
>> Now I wonder if the comment "We have to compile with -msse to use
>> xmmintrin.h" is still valid. I tried to tweak the following ifdef to
>> use the part of code, which includes <xmmintrin.h> and the it compiled
>> fine for me with CFLAGS="-O2 -m32" using recent versions of GCC and
>> Clang:
>>
>> http://cgit.freedesktop.org/pixman/tree/pixman/pixman-mmx.c?id=pixman-0.32.8#n63
>>
>> I believe that this might be somehow related to the new __ALL_ISA__
>> define, which had been mentioned in 2013:
>>     https://gcc.gnu.org/ml/gcc-patches/2013-04/txts5M0c0uU9y.txt
>>
>> So what about just dropping this ugly stuff and adding a configure
>> check, which would verify if the MMX code can include <xmmintrin.h>?
>
>
> I would love getting rid of the workarounds, but I'm somewhat worried about
> the possibility of regressions.
> If you believe is a valid option, we might definitely try to pursue it.
>
> What is the best way forward?

I've now reverted my commit and pushed yours.

Thanks.