Could we get a notice that if something breaks with customized CFLAGS (in the CFLAGS section), that the user is to try "-march= -O2" before reporting a bug? I've had bugreports from people who use : -march=pentium3 -O3 -pipe -fomit-frame-pointer -fexpensive-optimizations -fprefetch-loop-arrays -ffast-math -funroll-loops -foptimize-sibling-calls -freorder-blocks and it was only because of overoptimization that things refused to go through configure stage even.
In witch document to add this? Install guide? FAQs? somewhere else?
in the FAQ, preferrably directly after this section: I'm finding things to be really unstable and I'm using "-O9 -ffast-math -fomit-frame-pointer" optimizations. What gives? When you use any optimizations beyond -O3, you're really taking the risk of having broken packages. Very aggressive optimizations sometimes cause the compiler to streamline the assembly code to the point where it doesn't quite do the same thing anymore. Loc-Dog (on IRC) uses -O3 -mcpu=i686 -march=i686 -fforce-addr -fomit-frame-pointer -funroll-loops -frerun-cse-after-loop -frerun-loop-opt -malign-functions=4, which is about as much as I'd want to push global optimization settings. Beyond this, it's best to use ultra-high optimizations only with specific packages where you really need that extra 2%, (eg graphics and various multimedia programs), and where you can easily test the package to ensure that it hasn't been optimized into oblivion.
fixed in the CVS
