2014-02-06 Julian Taylor <jtaylor.deb...@googlemail.com>: > On 06.02.2014 00:39, Jaromír Mikeš wrote: > > > 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 >
Can you elaborate a bit here? When I builded in clean chroot (amd64) I never noticed that these flags would be added. > > > -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. > > > -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) > > > -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 > Thank you for commenting these flag. They looks like they shouldn't be generally applied in all cases. best regards mira
