On 2011-03-26 01:06, Caligo wrote: > On Fri, Mar 25, 2011 at 11:56 PM, Jonathan M Davis <[email protected]> wrote: > > On 2011-03-25 21:21, Caligo wrote: > >> On Fri, Mar 25, 2011 at 10:49 PM, Jonathan M Davis <[email protected]> > > > > wrote: > >> > On 2011-03-25 19:04, Caligo wrote: > >> >> T[3] data; > >> >> > >> >> T dot(const ref Vector o){ > >> >> return data[0] * o.data[0] + data[1] * o.data[1] + data[2] * > >> >> o.data[2]; } > >> >> > >> >> T LengthSquared_Fast(){ return data[0] * data[0] + data[1] * data[1] > >> >> + data[2] * data[2]; } > >> >> T LengthSquared_Slow(){ return dot(this); } > >> >> > >> >> > >> >> The faster LengthSquared() is twice as fast, and I've test with GDC > >> >> and DMD. Is it because the compilers don't inline-expand the dot() > >> >> function call? I need the performance, but the faster version is too > >> >> verbose. > >> > > >> > It sure sounds like it didn't inline it. Did you compile with -inline? > >> > If you didn't then it definitely won't inline it. > >> > > >> > - Jonathan M Davis > >> > >> I didn't know I had to supply GDC with -inline, so I did, and it did > >> not help. In fact, with the -inline option the performance gets worse > >> (for DMD and GDC), even for code that doesn't contain any function > >> calls. In any case, code compiled with DMD is always behind GDC when > >> it comes to performance. > > > > I don't know what gdc does, but you have to use -inline with dmd if you > > want it to inline anything. It also really doesn't make any sense at all > > that inlining would harm performance. If that's the case, something > > weird is going on. I don't see how inlining could _ever_ harm > > performance unless it just makes the program's binary so big that _that_ > > harms performance. That isn't very likely though. So, if using -inline > > is harming performance, then something weird is definitely going on. > > > > - Jonathan M Davis > > The only time that -inline has no effect is when I turn on -O3. This > is also when the code performs the best. I've never used -O3 in my > C++ code, but I guess things are different in D even with the same > back-end.
I really don't know what gdc does. With dmd, inlining is not turned on unless -inline is used. Also, -inline with dmd does not force inlining, it merely turns on the optimization. The compiler still chooses where and when it's best to inline. With gcc, I believe that inlining is normally turned on at a pretty low optimization level (probably -O), and like dmd, it chooses where and when it's best to inline, but unlike dmd, it uses the inline keyword in C++ as a hint as to what it should do. However, -O3 forces inlining on all functions marked with inline. How gdc deals with that given that D doesn't have an inline keyword, I don't know. Regardless, given what inlining does, I have a _very_ hard time believing that it would ever degrade performance unless it's buggy. - Jonathan M Davis
