On Thu, 20 Aug 2026 at 12:59, Yuao Ma <[email protected]> wrote: > > On Thu, Aug 20, 2026 at 6:31 PM Jonathan Wakely <[email protected]> wrote: > > > > On Thu, 20 Aug 2026 at 11:30, Jonathan Wakely <[email protected]> wrote: > > > > > > On Wed, 19 Aug 2026 at 17:23, Yuao Ma <[email protected]> wrote: > > > > > > > > Hi! > > > > > > > > Similar to std::for_each, this patch optimizes ranges::for_each for > > > > segmented iterators. > > > > > > If I understand correctly, this will break cases that require > > > std::invoke to invoke the function object, e.g. > > > > > > ranges::for_each(r, &T::f); > > > > A more concrete example: > > > > struct T { void f() { } }; > > std::deque<T> d; > > ranges::for_each(d, &T::f); > > > > deque's _S_for_each_segment just uses __func without std::invoke, doesn't > > it? > > > > Actually this will compile and run without error, and my local check > verifies this. I think the reason is that what we passed to the __func > is the internal lambda of the std::__for_each_segmented, rather than > the &T::f. The only place which will be called with member function is > correctly handled with std::invoke.
Ah yes! When ranges::__for_each stops recursing and calls the 'else' branch it uses std::__invoke. Nice. Is there any benefit to passing __f and __proj separately, using two parameter slots? ranges::__for_each could take a single __f with no proj, and then just call __f(*__first) in its else branch. And ranges::for_each could pass it a lambda which invokes proj and f. That would mean an additional indirection, but only passing one parameter. Maybe it's not an improvement. > > > > > > > > > > > > Fully tested on x86_64-linux with no regressions. > > > > > > > > Using the newly added benchmark, it shows a 3x improvement when using > > > > ranges::for_each with std::deque. > > > > > > > > === Wed Aug 19 03:28:22 PM UTC 2026 === > > > > for_each.cc std::for_each vector<int> 2r 1u 0s > > > > 0mem 0pf > > > > for_each.cc std::for_each deque<int> 2r 2u 0s > > > > 0mem 0pf > > > > for_each.cc std::for_each list<int> 13r 14u 0s > > > > 0mem 0pf > > > > for_each.cc std::ranges::for_each vector<int> 2r 2u > > > > 0s 0mem 0pf > > > > for_each.cc std::ranges::for_each deque<int> 6r 5u > > > > 0s 0mem 0pf > > > > for_each.cc std::ranges::for_each list<int> 13r 14u > > > > 0s 0mem 0pf > > > > === Wed Aug 19 04:09:51 PM UTC 2026 === > > > > for_each.cc std::for_each vector<int> 2r 1u 0s > > > > 0mem 0pf > > > > for_each.cc std::for_each deque<int> 2r 2u 0s > > > > 0mem 0pf > > > > for_each.cc std::for_each list<int> 13r 14u 0s > > > > 0mem 0pf > > > > for_each.cc std::ranges::for_each vector<int> 2r 2u > > > > 0s 0mem 0pf > > > > for_each.cc std::ranges::for_each deque<int> 2r 1u > > > > 0s 0mem 0pf > > > > for_each.cc std::ranges::for_each list<int> 13r 14u > > > > 0s 0mem 0pf > > > > > > > > Please take a look when you are available, thanks! > > > > > > > > Note: after preparing this patch I found the -std=gnu++11 in the check > > > > performance script based on Jonathan's guidance. I can prepare a patch > > > > for this tomorrow and get rid of the STD in the benchmark. > > > > > > > > Yuao > > >
