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

[Vladimir Kozlov]

On Fri, 6 Jun 2025 22:40:34 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 5 with) 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))

src/hotspot/share/opto/compile.cpp line 2540:

> 2538:       return;
> 2539:     }
> 2540:     mex.eliminate_opaque_looplimit_macro_nodes();

Missing `failing()` check.

src/hotspot/share/opto/macro.cpp line 2480:

> 2478: void PhaseMacroExpand::eliminate_opaque_looplimit_macro_nodes() {
> 2479:   if (C->macro_count() == 0)
> 2480:     return;

Code style: use {}.

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PR Review Comment: https://git.openjdk.org/jdk/pull/25682#discussion_r2138406210
PR Review Comment: https://git.openjdk.org/jdk/pull/25682#discussion_r2138399110