RFR: 8361140: Missing OptimizePtrCompare check in ConnectionGraph::reduce_phi_on_cmp [v4]

[Guanqiang Han]

> When running with `-XX:-OptimizePtrCompare` (which disables pointer comparison optimization), the compiler may hit an assertion failure in debug builds because `optimize_ptr_compare` is still being called. This violates the intended usage of the flag and leads to unexpected crashes.
> 
> This patch adds an early return to `reduce_phi_on_cmp` when `OptimizePtrCompare` is false. Since the optimization relies on `optimize_ptr_compare` for static reasoning about comparisons, there's no benefit in proceeding with `reduce_phi_on_cmp` when this flag is disabled.

Guanqiang Han has updated the pull request with a new target base due to a merge or a rebase. The incremental webrev excludes the unrelated changes brought in by the merge/rebase. The pull request contains seven additional commits since the last revision:

 - Remove the unused variable
 - Merge remote-tracking branch 'upstream/master' into 8361140
 - update regression test
 - Merge remote-tracking branch 'upstream/master' into 8361140
 - update modification and add regression test
 - Merge remote-tracking branch 'upstream/master' into 8361140
 - 8361140: Missing OptimizePtrCompare check in ConnectionGraph::reduce_phi_on_cmp
   
   When running with `-XX:-OptimizePtrCompare` (which disables pointer comparison optimization), the compiler may hit an assertion failure in debug builds because `optimize_ptr_compare` is still being called. This violates the intended usage of the flag and leads to unexpected crashes.
   
   This patch adds an early return to `reduce_phi_on_cmp` when `OptimizePtrCompare` is false. Since the optimization relies on `optimize_ptr_compare` for static reasoning about comparisons, there's no benefit in proceeding with `reduce_phi_on_cmp` when this support is disabled.

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Changes:
  - all: https://git.openjdk.org/jdk/pull/26125/files
  - new: https://git.openjdk.org/jdk/pull/26125/files/fd6f90f5..0e9aa956

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=26125&range=03
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=26125&range=02-03

  Stats: 377 lines in 16 files changed: 113 ins; 179 del; 85 mod
  Patch: https://git.openjdk.org/jdk/pull/26125.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/26125/head:pull/26125

PR: https://git.openjdk.org/jdk/pull/26125