On Sun, Dec 13, 2015 at 5:23 AM, Oded Gabbay <oded.gab...@gmail.com> wrote: > On Sun, Dec 13, 2015 at 11:56 AM, Jonathan Gray <j...@jsg.id.au> wrote: >> On Sat, Dec 12, 2015 at 06:41:56PM +0000, Emil Velikov wrote: >>> On 10 December 2015 at 08:42, Oded Gabbay <oded.gab...@gmail.com> wrote: >>> > On Wed, Dec 9, 2015 at 8:30 PM, Matt Turner <matts...@gmail.com> wrote: >>> >> On Tue, Dec 8, 2015 at 9:37 PM, Jonathan Gray <j...@jsg.id.au> wrote: >>> >>> Change the __m128i variables to be volatile so gcc 4.9 won't optimise >>> >>> all of them out with -O1 or greater. The _mm_set1_epi32/pinsrd calls >>> >>> still get optimised out but now there is at least one SSE4.1 instruction >>> >>> generated via _mm_max_epu32/pmaxud. When all of the sse4.1 instructions >>> >>> got optimised out the configure test would incorrectly pass when the >>> >>> compiler supported the intrinsics and the assembler didn't support the >>> >>> instructions. >>> >>> >>> >>> Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=91806 >>> >>> Signed-off-by: Jonathan Gray <j...@jsg.id.au> >>> >>> Cc: "11.0 11.1" <mesa-sta...@lists.freedesktop.org> >>> >>> --- >>> >>> configure.ac | 2 +- >>> >>> 1 file changed, 1 insertion(+), 1 deletion(-) >>> >>> >>> >>> diff --git a/configure.ac b/configure.ac >>> >>> index 260934d..1d82e47 100644 >>> >>> --- a/configure.ac >>> >>> +++ b/configure.ac >>> >>> @@ -384,7 +384,7 @@ CFLAGS="$SSE41_CFLAGS $CFLAGS" >>> >>> AC_COMPILE_IFELSE([AC_LANG_SOURCE([[ >>> >>> #include <smmintrin.h> >>> >>> int main () { >>> >>> - __m128i a = _mm_set1_epi32 (0), b = _mm_set1_epi32 (0), c; >>> >>> + volatile __m128i a = _mm_set1_epi32 (0), b = _mm_set1_epi32 (0), c; >>> >>> c = _mm_max_epu32(a, b); >>> >>> return 0; >>> >> >>> >> I would have extracted an int from the result of _mm_max_epu32 and >>> >> returned that instead of 0. >>> > >>> > Instead of the volatile I assume ? >>> > >>> Precisely. If anyone wants to follow on Matt's suggestion we can pick >>> that one as well. I'd like to get a patch for the next stable releases >>> (next Friday for 11.0.x and just after new year for 11.1.1) so I'll >>> take whatever's around :-) >>> >>> -Emil >> >> I avoided that as I wasn't sure if there was a case where autoconf >> cared about the return code. If someone wants to create a new diff >> feel free, I have limited connectivity till the middle of next week. > > So I'm not a huge SSE expert, but I tried doing this (remove volatile > and return _mm_cvtsi128_si32 of c): > > ------------------------ > #include <mmintrin.h> > #include <xmmintrin.h> > #include <emmintrin.h> > > int main () { > __m128i a = _mm_set1_epi32 (0), b = _mm_set1_epi32 (0), c; > c = _mm_xor_si128 (a, b); > return _mm_cvtsi128_si32(c); > } > ------------------------- > > When compiling with "gcc -O1 -msse2", gcc is 4.8.5 (from RHEL 7.2), I got: > > --------------------- > main: > .LFB521: > .cfi_startproc > movl $0, %eax > ret > .cfi_endproc > ------------------- > > So unless I misunderstood matt's suggestion, I think we *have* to use > the volatile as it forces the compiler to produce pxor and movdqa > assembly commands.
Since all the arguments to the intrinsics are constants, GCC is constant-evaluating them. I expect all you'd need to do is pass some global variables to the intrinsics or similar. _______________________________________________ mesa-dev mailing list mesa-dev@lists.freedesktop.org http://lists.freedesktop.org/mailman/listinfo/mesa-dev
