https://gcc.gnu.org/bugzilla/show_bug.cgi?id=102684
Bug ID: 102684
Summary: [missed optimization] std::min_element /
ranges::min_element does not get optimized away with
std::gcd
Product: gcc
Version: 11.2.1
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: xkeviota at gmail dot com
Target Milestone: ---
This code which calculates the gcd of the minimum and maximum element of a
range of elements gets optimized away entirely with clang to just a `return`
statement with `-O3` while gcc (trunk) produces up to 232 lines of assembly
depending on the optimization level
(https://compiler-explorer.com/z/TYrx5exP3).
#include <algorithm>
#include <numeric>
#include <span>
#include <vector>
namespace r = std::ranges;
template <typename T>
constexpr auto find_gcd(std::span<T> container) {
return std::gcd(*r::min_element(container),
*r::max_element(container));
}
int main() {
std::vector<int> ints = {2, 4, 6, 10};
return find_gcd<int>(ints);
}
The same happens when `std::min_element` is used for example. I found one other
post regarding `std::min_element` from 2018 about custom predicates but I
wasn't sure if it might have the same underlying problem.
