x86 Intrinsics for fma in Math Library

[Vladimir Kozlov]

Good suggestion. Need a test to confirm "correct" results matching result of assembler instruction.

Thanks,
Vladimir

On 7/21/16 3:01 AM, Andrew Haley wrote:
> On 20/07/16 21:08, Vladimir Kozlov wrote:
>> The only thing is worrying me is a constant folding (when all arguments
>> are constants) in C2 which uses libm fma() method (in subnode.cpp):
>>
>> return TypeD::make(fma(d1, d2, d3));
>>
>> It may produce different result than vfmadd231sd instruction so I would
>> like to remove this optimization (leave only TOP checks).
>
> This would be a shame.  We could leave the optimization in,
> but guard it with
>
> #ifdef __STDC_IEC_559__
>
> That would guarantee that fma() is compliant with IEC 559, and the
> C language specification says:
>
> F.9.10.1 The fma functions
>
> - fma(x, y, z) computes xy + z, correctly rounded once.
>
> Andrew.
>