RFR: JDK-8302736: Major performance regression in Math.log on aarch64

[Andrew Haley]

On Thu, 11 May 2023 01:44:08 GMT, Dean Long <dlong at openjdk.org> wrote:

> > The trade-off of course is that if we push this too far down we may have to execute it far more often and so take a performance hit. So figuring out the optimum placement for these in the call stack seems rather difficult.
> 
> Most code does not care what the WXWrite state is. We could use an alternative approach where code that needs a particular WXWrite state sets it, but when it is done not change the state back.

Yes, I agree. Given a very fast way to query the current state, we can do the transition the first time we need to write into the code cache. Given a very fast way to query the current state, we'd be fine.

We could even consider trapping on a fault, enabling WX then returning in some cases. I guess there's no reason that'd not work, but I may be wrong.

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PR Comment: https://git.openjdk.org/jdk/pull/13606#issuecomment-1543618358