RFR: 8283681: Improve ZonedDateTime offset handling [v3]

[Claes Redestad]

On Fri, 25 Mar 2022 15:16:42 GMT, Claes Redestad <redestad at openjdk.org> wrote:

>> Richard Startin prompted me to have a look at a case where java.time underperforms relative to joda time (https://twitter.com/richardstartin/status/1506975932271190017). 
>> 
>> It seems the java.time test of his suffer from heavy allocations due ZoneOffset::getRules allocating a new ZoneRules object every time and escape analysis failing to do the thing in his test. The patch here adds a simple specialization so that when creating ZonedDateTimes using a ZoneOffset we don't query the rules at all. This removes the risk of extra allocations and slightly speeds up ZonedDateTime creation for both ZoneOffset (+14%) and ZoneRegion (+5%) even when EA works like it should (the case in the here provided microbenchmark).
>
> Claes Redestad has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Override ZoneOffset::normalized, cache ZoneOffset::getRules, revert change to add 2nd parameter to ZoneId::getOffset

Thanks for reviews!

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PR: https://git.openjdk.java.net/jdk/pull/7957