On Tue, Sep 10, 2013 at 11:06 AM, Jan Hubicka <hubi...@ucw.cz> wrote: >> On 10/09/13 10:11, Jakub Jelinek wrote: >> > On Tue, Sep 10, 2013 at 10:06:04AM +0200, David Brown wrote: >> >> This last point is crucial. I haven't looked at the code in question, >> >> but one point to check is how the functions are called. If they are >> >> often called with constant values, then they may be very much simplified >> >> due to constant propagation. Secondly, if a function is inlined, the >> >> compiler has full knowledge of the effects of the function "call" and >> >> can thus optimise better (keeping data in registers over the "call", >> >> shuffling around loads and stores, etc.). Finally, if the functions are >> >> called in loops or other time-critical code, it can be worth spending >> >> more code section space for a faster result (but sometimes smaller code >> >> is faster due to caches, branch prediction buffers, etc.). >> >> >> >> The ideal situation is that LTO figures this out for you, and the code >> > >> > At least until LTO keeps to end up with unusable or hardly usable debug >> > info, effectively requiring LTO for good compiler performance is a >> > non-starter. And, the inliner we have is not dumb, if it sees an inline >> > function, but it is too large, it will usually not inline it. >> > So, rather than counting the lines of inline functions in headers, IMHO it >> > is better to look at inliner's decisions about those functions, if it >> > never inlines them, then supposedly moving them out of line is reasonable. >> > >> > Jakub >> > >> >> That should be easy enough with "-Winline", I think. > > What i also do from time to time is to do LTO profiledbootstrap and look into > inline dump. Then you have inlining ordered by pretty realistic measure of > benefits, so you see what matters and what not. > > Inliner knows that constant callbacks are good to inline and will bump up > its limits. > > One problem is that we do have those functions as static inlines, so they ends > up duplicated, with C++ we may consider moving them to comdat.
But then inlining / cloning is no longer cheap, no? And will be disabled at -O2? Richard. > Honza >> >> David
