On 09/11/2012 04:15 PM, Markus Trippelsdorf wrote: > On 2012.09.11 at 16:00 +0100, Andrew Haley wrote: >> On 09/11/2012 03:56 PM, Pete Flugstad wrote: >>> Hi, >>> >>> I'm trying to profile (using valgrind's callgrind) some code that >>> uses sin/cos and I'm seeing some things I'm not expecting. >>> >>> My OS is Ubuntu 12.04/x86_64, hardware is an Intel Xeon X5690. GCC >>> is the distro version, gcc (Ubuntu/Linaro 4.6.1-9ubuntu3) 4.6.1. I'm >>> compiling with -O2. >>> >>> The strange thing is that I'm seeing sincos (from libm.so) is >>> showing up in the callgrind output. From reading the manual, GCC >>> should replace our calls to sin and cos with __builtin_ versions, >>> right? >> >> Yes, it does, and one of the things that expanding the builtins does is >> call sincos(). > > BTW, s_sincos.S was removed from glibc a while ago. So if you're running > a recent glibc version you end up with the slow floating-point sin/cos > implementation, that causes a 50% slowdown. > See: http://sourceware.org/bugzilla/show_bug.cgi?id=14412 > > However Intel has recently posted fast SSE sin/cos/sincos versions for > libm (sinf, cosf and sincosf). I think gcc should be updated to call > those instead. Well, gcc will call whatever sincos is in the library. If there's a faster accurate way to do sincos(), glibc should do it. Andrew.
