On 2017-08-21 07:31 -0400, Jeffrey Walton wrote: > On Mon, Aug 21, 2017 at 7:20 AM, Marc Glisse <marc.glisse@xxxxxxxx> wrote: > > On Mon, 21 Aug 2017, Jeffrey Walton wrote: > > > > > 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. See <https://gcc.gnu.org/bugzilla/show_bug.cgi?id=67317>, or <https://gcc.gnu.org/ml/gcc-bugs/2015-08/msg01534.html> if you can't access Bugzilla. > Jeff -- Xi Ruoyao <ryxi@xxxxxxxxxxxxxxxxx> School of Aerospace Science and Technology, Xidian University
