RFR: 8340708: Optimize StackMapGenerator::processMethod [v3]

[Shaojin Wen]

> A small optimization of processMethod, by using local variables and extracting exception methods, reduces codeSize from 326 to 283

Shaojin Wen has updated the pull request incrementally with one additional commit since the last revision:

  reduce getFrame

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Changes:
  - all: https://git.openjdk.org/jdk/pull/21137/files
  - new: https://git.openjdk.org/jdk/pull/21137/files/ba35444b..ba1f9aa4

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=21137&range=02
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=21137&range=01-02

  Stats: 3 lines in 1 file changed: 1 ins; 1 del; 1 mod
  Patch: https://git.openjdk.org/jdk/pull/21137.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/21137/head:pull/21137

PR: https://git.openjdk.org/jdk/pull/21137