RFR: 8316493: Remove the caching fields in AbstractMap [v11]

[Chen Liang]

On Fri, 10 Nov 2023 08:17:22 GMT, Per Minborg <pminborg at openjdk.org> wrote:

>> This PR outlines a solution for making immutable maps `@ValueBased` by removing cacheing of certain values in `AbstractMap`.
>> 
>> By removing these caching fields in `AbstractMap`, we can make the immutable maps `@ValueBased` and at the same time, performance is likely improved because the JVM is probably able to optimize away object creation anyway via escape analysis. Also, all maps will occupy less space as we get rid of a number of objects and references stored for each map.
>> 
>> We need to benchmark this solution to better understand its implications.
>
> Per Minborg has updated the pull request with a new target base due to a merge or a rebase. The pull request now contains 14 commits:
> 
>  - Merge branch 'master' into vb-map2
>  - Fix formatting
>  - Remove caching in TreeMap
>  - Remove caching from CHM and CSLM
>  - Move back clone to original position
>  - Reintroduce AbstractMap::clone
>  - Add 'fresh' to implSpec
>  - Remove AbstractMap::clone
>  - Merge master
>  - Merge branch 'master' into vb-map2
>  - ... and 4 more: https://git.openjdk.org/jdk/compare/9cce9fe0...b1bfcd17

test/micro/org/openjdk/bench/java/util/HashMapViews.java line 48:

> 46: @Fork(1)
> 47: @State(Scope.Thread)
> 48: public class HashMapViews {

Can we test TreeMap too? WeakHashMap, IdentityHashMap, and EnumMap have specific key requirements that prevents testing unfortunately.

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PR Review Comment: https://git.openjdk.org/jdk/pull/15614#discussion_r1443347052