>> > > I'm trying to use _addcarryx_u64. GCC 7.1 is still generating ADD and >> > > ADC instead of ADCX or ADOX: >> > >> > Does that compute wrong values? Make the program slower? >> >> It looks like the values are computed correctly. >> >> I don't know the affect on performance. The only benchmarks I have are >> for add/adc. I can't get the adcx/adox generated to benchmark them. >> >> Compared to Intel ICC code generation, Intel's code is about 20% to 30% smaller. > > GCC once used ADCX but got silly results. So Uros disabled it. Well, that explains a lot. Thanks. I can't help but wonder why GCC defined __ADX__ when it does not support it. Perhaps GCC should emit a warning to save the next guy from wasting hours on the problem. Jeff
