Author: Robert Hyatt
Date: 18:21:54 12/22/02
Go up one level in this thread
On December 22, 2002 at 08:42:23, Joel wrote: >Hey all, > >Was reading some of the previous threads where the general consensus seemed to >be that the Intel C++ 7.0 compiler did a much better job at optimising than the >VC 6.0 Sp4 compiler did. > >My compiler knowledge is very limited - I have written a C compiler before (uni >assignment), but optimisation wasn't an issue. I have no real idea how an >optimising compiler goes about it's work. > >For the record I have an Athlon XP 2100+, and my engine is bitboard based. > >Having said that, I installed the Intel compiler, and tried compiling my latest >version of Bodo, and then ran my dodgy little speed benchmark on it. It was >actually slower than the VC 6.0 compiler, though I have reason to suspect my >incompetence is the issue, largely due to statements like: > >"Did you use the intel C++ 7.0? Of course not. Did you do the profile-feedback >optimizations? Probably not." > >What I am asking is how do I do this profile-feedback optimisations, and or any >other optimisations which you guys do? > >What would be particularly helpful is other people could give me the compiler >command line parameters they use to generate fast code. > >I really need to buy a book on optimising compilers so I understand what the >hell is happening here. :| > >Any help greatly appreciated, > >Joel Veness You need to compile with the options -prof_gen and -prof_dir <dirpath> options. You then run a set of what you think are "representative positions" thru the compiler. After you finish running whatever you want, you then recompile, but this time you replace the -prof_gen option with the -prof_use option and away it goes. After this compile, it will probably be 10% faster than compiling without this profiling approach.
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