callgrind and sin/cos under GCC

[Markus Trippelsdorf]

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. 

-- 
Markus