Vladimir Makarov (vmakarov@xxxxxxxxxx) said: > >Since I was a bit (intentionally) curt and dismissive in my other > >response in this thread, I'll add some anecdata here. I have actually > >tried building xserver with clang and running the standard set of > >microbenchmarks. I found one relevant path where the clang build was > >~15% faster [1]. Something like 60% of the rest were within ±3%. For > >everything else clang was uniformly worse by usually about 5%. > > > The another usual mistake when people compare speed of GCC and LLVM > is to use -O2 for the both compilers. But the true is that -O1 of > GCC is -O2 of LLVM with the point of code generation quality. The > compiler speed of GCC with -O1 is the same as for LLVM with -O2. > You can find the latest comparison of LLVM and GCC on > http://vmakarov.fedorapeople.org/spec/ (see 2011 comparison at the > bottom of the left frame). Speaking of potential magic bullets... is there any reason we don't enable auto-vectorization by default (with -O3, or with the assorted -f/-m flags?) - Is it not stable enough? - Does it not take effect often enough? - Is it not done generically enough that we would run into instruction set problems? (I belive on x86_64 we can assume SSE2. x86 is a mess, obvs.) Bill -- devel mailing list devel@xxxxxxxxxxxxxxxxxxxxxxx https://admin.fedoraproject.org/mailman/listinfo/devel
