On Tue, Sep 10, 2013 at 10:11 AM, Jakub Jelinek <ja...@redhat.com> 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.
I mostly agree. Though please also factor in IPA-CP - the reason that get_addr_base_and_unit_offset_1 is inline is that it receives a callback which in all call-sites is constant or NULL and optimizing that function is cruical (it will be usually called once in each TU and thus either inlined or cloned for IPA-CP). Also the operand iterators are very important to optimize, so outlining them is a non-starter. There isn't much code I'd expect we want to put back into .c files instead given that we now use C++ I'd expect more code to be moved into header files because of the use of templates. That's the way of life with C++ - you got what you wanted ;) Richard. > Jakub
