RFR(S) 8029302: Performance regression in Math.pow intrinsic

[Christian Thalinger]

I’ve said this before (see bug report) and I say it again (last time, I promise):  yes, it is a performance regression in the C2 compiler but a MUCH better place to “fix" this would be in the library.  Cover the common and special cases there and only use the intrinsic for the uncommon cases.

On Apr 17, 2014, at 7:21 AM, David Chase <david.r.chase at oracle.com> wrote:

> As long as we are doing this as a constant-driven transform in the compiler,
> it might not hurt to also consider the case of x**3.  Cubes are common enough.
> 
> David
> 
> 
> On 2014-04-17, at 11:45 AM, Vladimir Kozlov <vladimir.kozlov at oracle.com> wrote:
> 
>> Niclas,
>> 
>> Looking on __ieee754_pow() in sharedRuntimeTrans.cpp and it has other simple cases:
>> 
>> x**0 = 1
>> x**1 = x
>> x**-1  = 1/x
>> x**0.5 = sqrt(x)
>> 
>> It would be nice to know which are frequently used and implement them too.
>> 
>> Also there is check for NaN before all this cases except x**0 = 1:
>> 
>> /* +-NaN return x+y */
>> 
>> You need to test that new C2 code produces the same results for NaN values.
>> 
>> Thanks,
>> Vladimir
>