On Sun, 23 May 2010 11:06:24 +0200 Benjamin Zores <b...@geexbox.org> said:
> On Sun, May 23, 2010 at 6:22 AM, Carsten Haitzler <ras...@rasterman.com> > wrote: > > On Sat, 22 May 2010 23:46:56 +0200 Benjamin Zores <b...@geexbox.org> said: > > > > any reason you use just -O not -O2? > > > > fyi - no attached file - sf.net filtered it out. :) though generally this > > kind of a problem is a result of compiler issues - eg no neon support in > > gcc (or poor/older support) etc. generally anyway. > > It used to be -O4 actually. Then I just switch to -O just to ensure it > was not triggered by any compiler optimization bug. > Apparently this wasn't the case. aaah gotcha. tho in my experience -O2 is about as good as it gets without using -mtune/cpu etc to generate instructions for a specific architecture level or tune for it. at least in my experience. i have a suggestion. dont go about -O2 unless you can really justify it - that means benchmarks show real solid speedups (consistently more than 5%). in the past at least -O3 and above have also been wonderful sources of compiler bugs, that produce incorrect code - and you may end up suffering from bugs that don't actually exist in the code - but lie in the compiler, so... just beware of high -O levels. test to be sure it actually is worth it. do real benchmarking. remember it's a risk tradeoff - you gain N% more speed for a higher chance of bugs (that cant actually be fixed in the src - but in the compiler which makes it harder). thus why i say more than 5% - it is, of course, a fuzzy number, but it means "you need a real significant and noticeable speedup". for evas at any rate, use expedite and do benchmarks. better results come from higher -c counts (loop count - so the more loops it does the less you'll be hit by entropy - default is 128 - so use -c 256 if you are patient if you want very accurate results). as an example - results for x86 (32bit) evas speed (weighted): -O0 185.74 -O1 271.33 -O2 274.52 -O3 274.30 -O4 272.46 (all of them used -march=nocona as well in CFLAGS - on a core2 duo laptop). notice performance actually peaks at -O2 :) (also -O0 is horrible - but just to note - i write a lot of my code to assume a compiler will have a decent optimiser, so it will pick up the pieces with what may seem "stupid code", but that "sutpid code" is meant to be more readable/maintainable (need i get into -funroll-loops ?) :) -- ------------- Codito, ergo sum - "I code, therefore I am" -------------- The Rasterman (Carsten Haitzler) ras...@rasterman.com ------------------------------------------------------------------------------ _______________________________________________ enlightenment-devel mailing list enlightenment-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/enlightenment-devel
