RFR: 8376220: C2: Refactor the logic to in MemNode::find_previous_store [v3]

[Quan Anh Mai]

> Hi,
> 
> This patch refactors the logic in `MemNode::find_previous_store` and makes a small improvement to `MemNode::detect_ptr_independence`. An IR test accompanies the improvement.
> 
> Please take a look and share your thoughts, thanks a lot.

Quan Anh Mai has updated the pull request incrementally with one additional commit since the last revision:

  Fix test failures

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/29390/files
  - new: https://git.openjdk.org/jdk/pull/29390/files/ac27cabf..4a88d34b

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=29390&range=02
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=29390&range=01-02

  Stats: 35 lines in 2 files changed: 14 ins; 1 del; 20 mod
  Patch: https://git.openjdk.org/jdk/pull/29390.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/29390/head:pull/29390

PR: https://git.openjdk.org/jdk/pull/29390