On Sun, Oct 11, 2015 at 5:30 AM, Siarhei Siamashka < siarhei.siamas...@gmail.com> wrote:
> On Sun, 11 Oct 2015 04:53:08 +0300 > Siarhei Siamashka <siarhei.siamas...@gmail.com> wrote: > > > On Sat, 10 Oct 2015 16:03:53 -0700 > > Jeremy Huddleston Sequoia <jerem...@freedesktop.org> wrote: > > > > > > On Oct 10, 2015, at 13:48, Andrea Canciani <ranm...@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? Andrea And if this configure check fails (because of using an old compiler), > then simply disable MMX support when building pixman. > > -- > Best regards, > Siarhei Siamashka >
0001-mmx-Improve-detection-of-support-for-K-constraint.patch
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