RFR: 8341141: Optimize DirectCodeBuilder [v17]

[Shaojin Wen]

> Some DirectCodeBuilder related optimizations to improve startup and running performance:
> 1. Merge calls, merge writeU1 and writeU2 into writeU3
> 2. Merge calls, merge writeU1 and writeIndex operations
> 3. Directly use writeU1 instead of writeBytecode
> 4. Rewrite the implementation of load and store

Shaojin Wen has updated the pull request incrementally with two additional commits since the last revision:

 - optimize DirectClassBuilder::build
 - writeU2U2U2

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/21243/files
  - new: https://git.openjdk.org/jdk/pull/21243/files/e7b32d43..7029dfe7

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=21243&range=16
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=21243&range=15-16

  Stats: 59 lines in 5 files changed: 37 ins; 8 del; 14 mod
  Patch: https://git.openjdk.org/jdk/pull/21243.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/21243/head:pull/21243

PR: https://git.openjdk.org/jdk/pull/21243