On Thu, 06 Feb 2014 00:47:54 +0100, Julian Taylor wrote: > On 06.02.2014 00:39, Jaromír Mikeš wrote: >> >> Hi all, >> >> I would like to add some optimization flags for amd64 arch in some >> packages (mostly LV2 nad LADSPA plugins). >> I found these as candidates for amd64 arch: >> >> -msse -msse2 -mfpmath=sse > > this is enabled by default on amd64 > >> -ffast-math > > this is dangerous it changes results, sometimes significantly (e.g. for > complex numbers), only use if you don't care about correctness or have > verified its still correct.
IME, audio processing software can get away with it. Csound and its 400+ library of opcodes has been built with this option and I have had no complaints yet. What is dangerous about this options? I see a warning in the gcc docs, but how can I know if my program relies "on a precise definition of IEEE floating point"? > >> -ftree-vectorize > > this does sometimes slow programs down, usually only programs doing > numeric work profit from it, these usually enable it by themselves. > It is enabled by the -O3 optimization level. > it is mostly safe to use if you follow the C standard strictly (i.e. no > unaligned access of aliased variables) Audio processing software tend to be about numeric work ;) It is probably better to pass -O3 to performance critical code. > >> -mtune=generic > > should be the default, but you can safely change that to something else. > generic in gcc < 4.9 is I think pentium4 which is a very old chip. > > gcc-4.9 will change the default of it to bulldozer/intel-core btw: > http://gcc.gnu.org/gcc-4.9/changes.html My experience is that -mtune=generic provides a great boost over no - mtune, at least on i386 when I tested it. I have just tested again on amd64 and it makes no difference. -- Saludos, Felipe Sateler -- To UNSUBSCRIBE, email to debian-devel-requ...@lists.debian.org with a subject of "unsubscribe". Trouble? Contact listmas...@lists.debian.org Archive: http://lists.debian.org/ld03jt$8d5$1...@ger.gmane.org