inline functions

[Caligo]

On Fri, Mar 25, 2011 at 11:56 PM, Jonathan M Davis <jmdavisProg at gmx.com> wrote:
> On 2011-03-25 21:21, Caligo wrote:
>> On Fri, Mar 25, 2011 at 10:49 PM, Jonathan M Davis <jmdavisProg at gmx.com>
> 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.