> On Fri, 25 Jun 2010, it was written: > > On Thu, Jun 24, 2010 at 11:50:52AM -0700, Taras Glek wrote: > > > We switched gcc4.3 for gcc4.5 and our automated benchmarking > > > infrastructure reported 4-19% slowdown on most of our performance > > > metrics on 32 and 64bit Linux. > > > > Could you please also try gcc4.4, so that it is clear if the slowdowns > > are between 4.3 and 4.4 or 4.4 and 4.5? Would be nice to narrow the changes > > a little bit. > > There sure is something in 4.5. I've seen a 1-10% slowdown at the GiNaC > (a computer algebra library) benchmark suite after switching from 4.4 to > 4.5 on x86_64 when compiling with -O2. And there hasn't been a measurable > performance differences between 4.3 and 4.4.
FP intensive code could be also affected by: On x86 targets, code containing floating-point calculations may run significantly slower when compiled with GCC 4.5 in strict C99 conformance mode than they did with earlier GCC versions. This is due to stricter standard conformance of the compiler and can be avoided by using the option -fexcess-precision=fast; also see below. (see http://gcc.gnu.org/gcc-4.5/changes.html) If not, I would be interested to take a look. C++ code in general tends to challenge inliner heruistic. We assembled a benchmark suite that we use for tunning the interprocedural optimizers pretty much every release. So perhaps GiNaC can be used as one of the tests. Honza > > -richy. > -- > Richard B. Kreckel > <http://www.ginac.de/~kreckel/>