I know you're going to reply with "BUT MY PREPROCESSOR", but template specialization is a big win and improvement (see qsort vs std::sort).
https://github.com/openzfs/zfs/commit/677c6f8457943fe5b56d7a...
The performance gain comes not from eliminating the function overhead, but enabling conditional move instructions to be used in the comparator, which eliminates a pipeline hazard on each loop iteration. There is some gain from eliminating the function overhead, but it is tiny in comparison to eliminating the pipeline hazard.
That said, C++ has its weaknesses too, particularly in its typical data structures, its excessive use of dynamic memory allocation and its exception handling. I gave an example here:
https://news.ycombinator.com/item?id=43827857
Honestly, I think these weaknesses are more severe than qsort being unable to inline the comparator.
Does not work if the compiler can not look into the function, but the same is true in C++.
Edit: It sort of works for the bsearch() standard library function:
https://godbolt.org/z/3vEYrscof
However, it optimized the binary search into a linear search. I wanted to see it implement a binary search, so I tried with a bigger array:
https://godbolt.org/z/rjbev3xGM
Now it calls bsearch instead of inlining the comparator.
That's not the most general case, but it's better than I expected.
That said, this brings me to my original reason for checking this, which is to say that it did not use a cmov instruction to eliminate unnecessary branching from the loop, so it is probably slower than a binary search that does:
https://en.algorithmica.org/hpc/data-structures/binary-searc...
That had been the entire motivation behind this commit to OpenZFS:
https://github.com/openzfs/zfs/commit/677c6f8457943fe5b56d7a...
It should be possible to adapt this to benchmark both the inlined bsearch() against an implementation designed to encourage the compiler to emit a conditional move to skip a branch to see which is faster:
https://github.com/scandum/binary_search
My guess is the cmov version will win. I assume merits a bug report, although I suspect improving this is a low priority much like my last report in this area: