RFR: 8354899: Reduce overhead associated with type switches [v2]

[Chen Liang]

> The downcallHandle method in Linker has a complex implementation, and type switches is triggered in multiple places in that handle.
> 
> After bytestacks analysis of a simple program that links the native implementation of Class::forName0, it turns out that:
> 1. there are a few missed usages of type switch in ClassFile API
> 2. type switch can speed up generation by using explicit stack maps, as stack map gen is over 50% of the generation instructions because the switch is branch-heavy, but the frames are actually simple.
> 
> These two combined are not that significant in the overall overhead of downcallHandle, but would be helpful for other workloads.

Chen Liang has updated the pull request with a new target base due to a merge or a rebase. The incremental webrev excludes the unrelated changes brought in by the merge/rebase. The pull request contains four additional commits since the last revision:

 - Rollback classfile boot speed changes
 - Merge branch 'master' of https://github.com/openjdk/jdk into fix/switch-gen-speed
 - Fix adding potentially unbound labels
 - 8354899: Reduce overhead associated with type switches

-------------

Changes:
  - all: https://git.openjdk.org/jdk/pull/24705/files
  - new: https://git.openjdk.org/jdk/pull/24705/files/cbc3fd34..2c17dd1c

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=24705&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=24705&range=00-01

  Stats: 21331 lines in 383 files changed: 18828 ins; 1542 del; 961 mod
  Patch: https://git.openjdk.org/jdk/pull/24705.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/24705/head:pull/24705

PR: https://git.openjdk.org/jdk/pull/24705