RFR: JDK-8210858: AArch64: remove Math.log intrinsic [v2]

[Tobias Holenstein]

On Thu, 18 Jan 2024 14:44:25 GMT, Tobias Holenstein <tholenstein at openjdk.org> wrote:

>> [JDK-8215133](https://bugs.openjdk.org/browse/JDK-8215133) disabled vmIntrinsics::_dlog. Remove it now
>> 
>> ### Why remove
>> 
>> That Java  specification says:
>> 
>> "The computed result must be within 1 ulp of the exact result. Results must be semi-monotonic... whenever the mathematical function is non-decreasing, so is the floating-point approximation, likewise, whenever the mathematical function is non-increasing, so is the floating-point approximation"
>> 
>> There is no proof of the monotonicity of this intrinsics at the moment.
>
> Tobias Holenstein has updated the pull request incrementally with one additional commit since the last revision:
> 
>   remove MacroAssembler::fast_log() and generate_dlog()

> > Separately, I do wonder if [JDK-8301202](https://bugs.openjdk.org/browse/JDK-8301202) gives us a reason to avoid even calling to runtime, and instead just stay in Java completely.
> 
> Yes, would be nice to stay in Java. We had a similar discussion in #13606 where I benchmarked the intrinsics on different platforms. But, they still gave up to 40% performance improvement vs. staying in java. I don't think much has changed performance wise since then..

@jddarcy any thoughts on that?

Perhaps I should re-run the benchmarks from May 2023..

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PR Comment: https://git.openjdk.org/jdk/pull/17480#issuecomment-1903912495