flat_map slow insertion introduced in boost-1.80.0

[biljazovic]

Hello,

I noticed that inserting elements in flat_map<int,int> is around 2 times slower going from version boost-1.79.0 to boost-1.80.0. I've found the relevant commit, 0d5068.

Sample code that is 2x faster when said commit is reverted:

#include <boost/container/flat_map.hpp>

int main() {
    boost::container::flat_map<int, int> m_flat_map;
    for (int i = 100000; i >= 0; --i) m_flat_map[i] = 1;
    return 0;
}

compiler: clang 15.0.7, linux-gnu platform

[psiha]

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