RFR: 8325478: Restructure the macro expansion compiler phase to not include macro elimination [v8]

[Vladimir Kozlov]

On Tue, 1 Jul 2025 16:28:27 GMT, Saranya Natarajan <snatarajan at openjdk.org> wrote:

>> This changeset restructures the macro expansion phase to not include macro elimination and also adds a flag StressMacroElimination which randomizes macro elimination ordering for stress testing purposes.
>> 
>> Changes:
>> - Implemented a method `eliminate_opaque_looplimit_macro_nodes` that removes the functionality for eliminating Opaque and LoopLimit nodes from the `expand_macro_nodes ` method. 
>> - Introduced compiler phases` PHASE_AFTER_MACRO_ELIMINATION` 
>> -  Added a new Ideal phase for individual macro elimination steps. 
>> - Implemented the flag `StressMacroElimination`. Added functionality tests for `StressMacroElimination`, similar to previous stress flag `StressMacroExpansion` ([JDK-8317349](https://bugs.openjdk.org/browse/JDK-8317349)).
>> 
>> Below is a sample screenshot (IGV print level 4 ) mainly showing the new phase .
>> ![image](https://github.com/user-attachments/assets/16013cd4-6ec6-4939-ac66-33bb03d59cd6)
>> 
>> Questions to reviewers: 
>> - Is the new macro elimination phase OK, or should we change anything?
>> - In `compile.cpp `, `PHASE_ITER_GVN_AFTER_ELIMINATION` follows `PHASE_AFTER_MACRO_ELIMINATION` in the current fix. Should `PHASE_ITER_GVN_AFTER_ELIMINATION` be removed ? 
>> 
>> Testing:
>> GitHub Actions
>> tier1 to tier5 on windows-x64, linux-x64, linux-aarch64, macosx-x64, and macosx-aarch64.
>> Tested that thousands of graphs are correctly opened and visualized with IGV using the same test used in  ([JDK-8317349](https://bugs.openjdk.org/browse/JDK-8317349))
>
> Saranya Natarajan has updated the pull request incrementally with one additional commit since the last revision:
> 
>   review comments fix part 1

Good.

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Marked as reviewed by kvn (Reviewer).

PR Review: https://git.openjdk.org/jdk/pull/25682#pullrequestreview-2976289575