https://gcc.gnu.org/bugzilla/show_bug.cgi?id=116958
Bug ID: 116958
Summary: [missed optimization] std::views::transform loses
track of the range size
Product: gcc
Version: 15.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: libstdc++
Assignee: unassigned at gcc dot gnu.org
Reporter: avi at scylladb dot com
Target Milestone: ---
Consider
```
#include <ranges>
#include <span>
#include <vector>
#include <functional>
std::vector<int> add1(std::span<int> r) {
return r
| std::views::transform(std::bind_front(std::plus<int>(), 1))
| std::ranges::to<std::vector>();
}
```
If I comment out the line calling transform(), it compiles to a call to
operator new + memcpy. As is, it compiles to a traditional expanding vector
loop. Since transform() doesn't change the size, it could have returned a
sized_range which to()/vector<> could have used to reserve the right size in
advance.
https://godbolt.org/z/xaae1oMnf
