Gentoo Archives: gentoo-user-fr

From: Guillaume Morin <webmaster@×××××××××××××.fr>
To: gentoo-user-fr@g.o
Subject: Re: [gentoo-user-fr] le systeme ne boote pas..
Date: Wed, 30 Jul 2003 12:25:28
In Reply to: Re: [gentoo-user-fr] le systeme ne boote pas.. by Montier Jacques
Montier Jacques a écrit :

>Merci aussi pour l'info sur l'erreur de frappe du commutateur -o3 ; >cela a-t-il eu une incidence sur le résultat de la compilation ?? > >Jacques > >
Oui bien sûr cela a une influence. L'option "-O" et ses variantes "-Ox" permettent d'optimiser le code. "-O" ou "-O1" est la plus faible optimisation, "-O3" en théorie la plus performante (mais c'est à voir, en effet dans de nombreux cas "-O2" est plus efficace). Un des gros intérêts de Gentoo est d'optimiser la compilation pour sa machine, et ça mérite donc un petit peu de temps de réflexion. Tu trouveras sur la page suivante la présentation des meilleurs options de compilation en fonction de ton processeur : Tout ceci est décrit dans le manuel de gcc (man gcc) : Options That Control Optimization These options control various sorts of optimizations: -O -O1 Optimize. Optimizing compilation takes somewhat more time, and a lot more memory for a large function. Without -O, the compiler's goal is to reduce the cost of compila- tion and to make debugging produce the expected results. State- ments are independent: if you stop the program with a breakpoint between statements, you can then assign a new value to any variable or change the program counter to any other statement in the func- tion and get exactly the results you would expect from the source code. With -O, the compiler tries to reduce code size and execution time, without performing any optimizations that take a great deal of com- pilation time. -O2 Optimize even more. GCC performs nearly all supported optimiza- tions that do not involve a space-speed tradeoff. The compiler does not perform loop unrolling or function inlining when you spec- ify -O2. As compared to -O, this option increases both compilation time and the performance of the generated code. -O2 turns on all optional optimizations except for loop unrolling, function inlining, and register renaming. It also turns on the -fforce-mem option on all machines and frame pointer elimination on machines where doing so does not interfere with debugging. Please note the warning under -fgcse about invoking -O2 on programs that use computed gotos. -O3 Optimize yet more. -O3 turns on all optimizations specified by -O2 and also turns on the -finline-functions and -frename-registers options. -O0 Do not optimize. -Os Optimize for size. -Os enables all -O2 optimizations that do not typically increase code size. It also performs further optimiza- tions designed to reduce code size. If you use multiple -O options, with or without level numbers, the last such option is the one that is effective. -- gentoo-user-fr@g.o mailing list