On Thu, 7 Sep 2023 11:13:44 GMT, Per Minborg <pminb...@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. The microbenchmark is deliberately minimalist and mainly verifies that the JIT _can_ eliminate allocation of the `keySet` and `values` and is as such a good starting point for further analysis. Worth noting also that eliminating these two transient fields would save 8-16 bytes from every `HashMap`, `LinkedHashMap`, `Map.of(..)` et.c. ------------- PR Comment: https://git.openjdk.org/jdk/pull/15614#issuecomment-1710352704
