On 7/3/08, Lee, Newbie <utmw0@xxxxxxxxxxx> wrote: > I thought function inlining is simple and easy thing. Inlining didn't become common until the mid 1980s. If it were easy, it would have happened earlier. :-) > But I read that gcc doesn't make function inline without > optimization flag, and function inlining is the last thing to do > when gcc optimize something. > > So I compiled a cpp file with -S and -O1, -O2, -O3 flags. > Document says that only -O3 turns on function inlining, but with > -O2, gcc also eliminated function calls. The result was better > than I expected. Part of the confusion may come from the kind of inlining. - Inlining of functions that are declared inline. - Inlining of functions that are not declared inline. The latter generally occurs only at higher optimization levels. > But I am confusing. > > 0. Does 'gcc -O2' make functions inline? If you declared them inline, yes. > 1. Is function inlining is dangerous? Yes, but only when used with linker interposition. Most functions are unaffected by inlining. > 2. Is 'gcc -O3 ' safe? (I heard -O2 is recommended) Higher levels of optimization will cause more of your bugs to activate. So, it all depends on what bugs you have in your code. > and any advice about this will help me. Write bug-free code. :-) Failing that, lots of tests help. -- Lawrence Crowl
