RFR: 8345485: C2 MergeLoads: merge adjacent array/native memory loads into larger load [v3]

[kuaiwei]

> WIP.
> 
> It worked for cases in the TestMergeLoads.java and can observe performance improvement in MergeLoadBench.getIntB . Need to check more cases.

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

  Add tests

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Changes:
  - all: https://git.openjdk.org/jdk/pull/24023/files
  - new: https://git.openjdk.org/jdk/pull/24023/files/7a1c524d..fb6cd3d7

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=24023&range=02
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=24023&range=01-02

  Stats: 304 lines in 3 files changed: 293 ins; 4 del; 7 mod
  Patch: https://git.openjdk.org/jdk/pull/24023.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/24023/head:pull/24023

PR: https://git.openjdk.org/jdk/pull/24023