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Re: GCC does not generate ADCX or ADOX for _addcarryx_u64

>> > > 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
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