https://gcc.gnu.org/bugzilla/show_bug.cgi?id=55212
--- Comment #101 from Kazumoto Kojima <kkojima at gcc dot gnu.org> --- > Perhaps the both codes are ok, though something odd happens > on atomic things anyway. I've forgotten that some atomic builtins fail with spill_failure in class 'R0_REGS' for old RA. So libstdc++-v3 was configured so to undefine _GLIBCXX_ATOMIC_BUILTINS for old RA and we see the above difference. I've tried to disable it on LRA build and rebuild libstdc++-v3 libs. 14.exe still fails and it looks very sensitive with code/option changes. Weird.
