Since Compact Strings implementation, there are simple methods in String and StringBuilders: coder(), value(), isLatin1(). They are mostly there to capture COMPACT_STRINGS settings that would fold to "false" when compact strings are disabled with -XX:-CompactStrings.

This was to guarantee the same performance when Compact String are unimplemented and/or have surprising performance behaviors. Quite some time had passed since JDK 9 release, and we can consider simplifying these.

Prototype patch improves the startup performance on Hello World, about 0.5 msec (or ~1.6%) less time spent. The improvement is quite probably more pronunciated on larger workloads, i.e. large application servers.

Draft PR:
 https://github.com/openjdk/jdk/pull/2334