As of boost 1.85, any key is found in any non-empty flat_multimap

[spth]

Consider this simple test program:

#include <iostream>
#include <boost/container/flat_map.hpp>

typedef boost::container::flat_multimap<int, short> operand_map_t;

operand_map_t o;

int main(void)
{
    o.insert(std::pair<int, short>(93, 48));
    if (o.find(97) != o.end())
        std::cout << "Boost is broken!\n";
    return 0;
}

When using boost 1.85, and compiling with GCC 13.2.0 at -O2, I get the "Boost is broken!" output. I do not see the bug when using boost 1.83. I do not know if this is a GCC or boost bug. I found the bug on Debian GNU/Linux on amd64, when looking into https://sourceforge.net/p/sdcc/bugs/3739/. Since that bug was reported by an SDCC user, multiple people have already run into this problem.

[iv-m]

Consider this simple test program

First, this is obviously a strict aliasing problem, as adding -fno-strict-aliasing to the compiler command line makes the program function correctly. So, as is pointed in the sdcc bug, this may be related (or same issue) as https://github.com/boostorg/container/issues/252.

git bisect with this example as the test shows that 1a4a205ea6ef7b4e67a2faab7c7d745711807695 is the first broken commit. Indeed, reverting it on top of tag boost-1.85.0 (6e697d796897b32b471b4f0740dcaa03d8ee57cc) fixes this issue for me.

[igaztanaga]

Thanks for the report. Hopefully this problem was fixed in commit (post 1.85):

https://github.com/boostorg/container/commit/20ad12f20e661978e90dc7f36d8ab8ac05e5a5a9

I see that gentoo has applied a patch based on that commit resolving the issue.