https://gcc.gnu.org/bugzilla/show_bug.cgi?id=88971
--- Comment #8 from rguenther at suse dot de <rguenther at suse dot de> --- On Tue, 22 Jan 2019, maratrus at mail dot ru wrote: > https://gcc.gnu.org/bugzilla/show_bug.cgi?id=88971 > > --- Comment #7 from Marat Stanichenko <maratrus at mail dot ru> --- > (In reply to rguent...@suse.de from comment #6) > > > Do you believe that compiler can do better in such situations? Or the > > > current > > > behaviour is perfectly valid and no improvements are really needed? > > > > The compiler can of course do better when estimating the benefit of > > inlining. It's just not entirely clear if it is reasonably easy to > > do so ... [let aside the -finline-function issue] > > Is it only about inlining? > > Unfortunately, I cannot evaluate the technical difficulties but in patterns > like presented here i.e. > > ``` > if (condition) > Function(param); > ``` > > irrespective of the fact whether `Function()` is asked to be inlined or not > there are at least two observations that the compiler may notice before taking > an optimization decision: > > a) Whether `Function(param)` is empty or not. In both scenarios in the example > presented `PrintBad<false>("<", ">", t)` and `PrintGood<false>("<", t)` are > actually empty. > > b) Whether `param` is used in a `Function`. I think I can see the examples > when > function calls like `PrintBad<false>(">", t)` generates a code to construct > parameter ">" despite the fact that not only it is not used but also the > function body is empty. > > Of course, ideally I expect the parameter not to be constructed if it is not > used and the whole branch to be eliminated of the `Function` is empty and > `condition` does not have side effects. But as I said, I do not have enough > technical expertise to evaluate the cost. I speak from a solely user's > perspective. > > What do you think is the best way to solve this? Keep tracking examples until > some critical mass is collected? Well, it's more until any bright idea pops up how to solve this abstraction issue...
