On Wed, 18 Nov 2015 14:22:09 -0800 Matt Turner <matts...@gmail.com> wrote:
> On Sun, Oct 11, 2015 at 10:34 AM, Andrea Canciani <ranm...@gmail.com> wrote: > > 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? > > I've now reverted my commit and pushed yours. Oh, thanks. Though it is always a good idea to give a short notice before landing patches to git, especially controversial ones. What we had in pixman-0.33.4 was not exactly bad. Sure, GCC did not detect MMX support, but the other compilers had no problems with it. In a way, this was a good thing because GCC is known to have a broken _mm_empty() intrinsic handling and it is probably not going to be ever fixed: https://gcc.gnu.org/PR47759 In the case of pixman, it happened to cause problems on more than one occasion. We do have a test in the test suite, which can detect x87 registers corruption caused by a misplaced EMMS instruction due to compiler optimizations. But not everyone runs the test suite for 32-bit pixman builds on x86 with PIXMAN_DISABLE="sse2 ssse3" regularly enough. It is not like we want to retire the MMX support just because it is old and out of fashion. The reason is that it is a source of recurring troubles. Sigh. Let's see how long will it take until the MMX code breaks again with one compiler version or another. -- Best regards, Siarhei Siamashka _______________________________________________ Pixman mailing list Pixman@lists.freedesktop.org http://lists.freedesktop.org/mailman/listinfo/pixman
