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

[Christian Hagedorn]

On Fri, 11 Jul 2025 00:37:10 GMT, Guanqiang Han <duke at openjdk.org> wrote:

>> 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.

Looks good, thanks! I'll give this a spinning in our testing and report back again.

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

Marked as reviewed by chagedorn (Reviewer).

PR Review: https://git.openjdk.org/jdk/pull/26125#pullrequestreview-3008979770