Your proposed modification to my patch makes sense. I’m not certain when I”ll have time to perform it.
> On Sep 17, 2017, at 6:40 AM, Siarhei Siamashka <siarhei.siamas...@gmail.com> > wrote: > > On Mon, 7 Aug 2017 07:52:29 -0700 > Rob Tsuk <r...@tsuk.com <mailto:r...@tsuk.com>> wrote: > >> From 662b17d0d691b567a3343af3439f5fbefe989584 Mon Sep 17 00:00:00 2001 >> From: Rob Tsuk <robt...@google.com> >> Date: Mon, 7 Aug 2017 07:11:10 -0700 >> Subject: [PATCH 1/1] Fix test for GCC vector extensions >> >> The previous test was getting a false positive for >> clang version 4. >> --- >> configure.ac | 2 +- >> 1 file changed, 1 insertion(+), 1 deletion(-) >> >> diff --git a/configure.ac b/configure.ac >> index e833e45..cbebc82 100644 >> --- a/configure.ac >> +++ b/configure.ac >> @@ -1101,7 +1101,7 @@ support_for_gcc_vector_extensions=no >> AC_MSG_CHECKING(for GCC vector extensions) >> AC_LINK_IFELSE([AC_LANG_SOURCE([[ >> unsigned int __attribute__ ((vector_size(16))) e, a, b; >> -int main (void) { e = a - ((b << 27) + (b >> (32 - 27))) + 1; return e[0]; } >> +int main (void) { __builtin_shuffle(a,b);e = a - ((b << 27) + (b >> (32 - >> 27))) + 1; return e[0]; } >> ]])], support_for_gcc_vector_extensions=yes) >> >> if test x$support_for_gcc_vector_extensions = xyes; then > > Thanks, the patch looks mostly good. We indeed have to add > the use of __builtin_shuffle() to the configure check code > snippet because it is used by pixman and Clang implements > this functionality in a different and incompatible way. > > We did not see this problem with older versions of Clang > because it did not support the shift vector by scalar operation > in its vector extensions. > > Too bad that GCC and Clang parted their ways and we can't have > a single unified implementation. The whole reason to use GCC > vector extension was that we could avoid platform-dependent > intrinsics in this code. > > About the patch. It would be great to use the result of > __builtin_shuffle() in the intermediate calculations just in > case. See > > https://cgit.freedesktop.org/pixman/commit/?id=a566f627dbd6ea8f2cba70a446e62caaa2ecbd26 > > <https://cgit.freedesktop.org/pixman/commit/?id=a566f627dbd6ea8f2cba70a446e62caaa2ecbd26> > > -- > Best regards, > Siarhei Siamashka
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