https://gcc.gnu.org/bugzilla/show_bug.cgi?id=115345
--- Comment #8 from Jakub Jelinek <jakub at gcc dot gnu.org> --- Also, if building with GCC 11 works and with GCC 12 doesn't, can you build two trees, one with either compiler and then bisect first among the shared libraries or binaries (find out which shared library or binary is affected), among the static libraries (GCC 11 and 12 ought to be ABI compatible, so try linking some *.a libraries from one build and other from another build, among the object files (start with linking half of the objects built by one compiler and another half by another compiler and depending on if it works as expected or not change the set of objects to link). If you get to one object file which when compiled with GCC 11 works even when everything else has been compiled with GCC 12 or vice versa, you can then try different options on that one (e.g. the -fno-strict-aliasing Andrew mentioned, -O0 etc.), and/or bisect inside of the source using #pragma GCC optimize(0) etc. Anyway, if there is a single translation unit like that and ideally if you find out which function is problematic, trying to stub functions it calls and add a caller which calls that single function with the right arguments turns it into a self-contained reproducer.
