https://gcc.gnu.org/bugzilla/show_bug.cgi?id=102059
--- Comment #6 from Martin Liška <marxin at gcc dot gnu.org> --- And the OPTION_MASK_P8_FUSION mask is set here: /* Enable power8 fusion if we are tuning for power8, even if we aren't generating power8 instructions. Power9 does not optimize power8 fusion cases. */ if (!(rs6000_isa_flags_explicit & OPTION_MASK_P8_FUSION)) { if (processor_target_table[tune_index].processor == PROCESSOR_POWER8) rs6000_isa_flags |= OPTION_MASK_P8_FUSION; else rs6000_isa_flags &= ~OPTION_MASK_P8_FUSION; }