More Info on GCC 4.x can be found in this nicely-written summary: http://www.ibm.com/developerworks/linux/library/l-gcc4/index.html
On Tue, Sep 15, 2009 at 11:05 PM, Paolo Falcone <[email protected]> wrote: > The "never ever use -O3" isn't an absolute rule. > > What the -O3 optimization flag does are turning on the following > options: -finline-functions, -funswitch-loops, -fpredictive-commoning, > -fgcse-after-reload and -ftree-vectorize. These, when coupled with > good code, can produce remarkable differences if you compare them with > the results from -O2 given that the compiler is free to optimize the > code by inlining functions, using vectorization on tree structures > (rather than processing it serially), .It is true that with inlining, > etc, there's a possibility that you can get bigger binaries and > greater memory usage - but at the price of faster performing code. > > There are other known flags that you can use like -findirect-inlining > that you can use if you compile with profile-guided optimizations. > > Use these if you know your code well. Otherwise, refer to the rule of > thumb. There has been tons of improvements in the 4.x line, especially > if you're into C++. But those aren't excuses for unnecessary "ricing". > > Hard disk and memory are getting cheaper nowadays... long ago 4GB of > RAM and 500GB of disk space is something you'll spend beyond 5 > digits... > > if you can produce static binaries for performance-sensitive stuff > that will be better. > > > On Tue, Sep 15, 2009 at 6:11 PM, Jimmy Lim <[email protected]> wrote: >> On Mon, Sep 14, 2009 at 11:37 PM, Alec Joseph Rivera <[email protected]> >> wrote: >>> Currently, we use GCC with -O3 and target i686 as the LCD for our >>> compilation. >> >> Rule of thumb, never ever use -O3 optimization on gcc-4.x.x. >> >> [0] -O3: This is the highest level of optimization possible, and also >> the riskiest. It will take a longer time to compile your code with >> this option, and in fact it should not be used system-wide with gcc >> 4.x. The behavior of gcc has changed significantly since version 3.x. >> In 3.x, -O3 has been shown to lead to marginally faster execution >> times over -O2, but this is no longer the case with gcc 4.x. Compiling >> all your packages with -O3 will result in larger binaries that require >> more memory, and will significantly increase the odds of compilation >> failure or unexpected program behavior (including errors). The >> downsides outweigh the benefits; remember the principle of diminishing >> returns. Using -O3 is not recommended for gcc 4.x. >> >> [0] http://www.gentoo.org/doc/en/gcc-optimization.xml >> >> -- >> Jimmy B. Lim >> j i m m y b l i m @ g m a i l . c o m >> _________________________________________________ >> Philippine Linux Users' Group (PLUG) Mailing List >> http://lists.linux.org.ph/mailman/listinfo/plug >> Searchable Archives: http://archives.free.net.ph >> > > > > -- > Paolo > -- Paolo _________________________________________________ Philippine Linux Users' Group (PLUG) Mailing List http://lists.linux.org.ph/mailman/listinfo/plug Searchable Archives: http://archives.free.net.ph
