RFR: 8339205: Optimize StackMapGenerator [v6]

[Shaojin Wen]

> Reduce code size by combining calls and defining local variables

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

  use 4 spaces.

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Changes:
  - all: https://git.openjdk.org/jdk/pull/20756/files
  - new: https://git.openjdk.org/jdk/pull/20756/files/eca48ba0..c03758ea

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=20756&range=05
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=20756&range=04-05

  Stats: 7 lines in 1 file changed: 0 ins; 0 del; 7 mod
  Patch: https://git.openjdk.org/jdk/pull/20756.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/20756/head:pull/20756

PR: https://git.openjdk.org/jdk/pull/20756