RFR: 8317349: Randomize order of macro node expansion in C2

[Roberto Castañeda Lozano]

On Fri, 2 Feb 2024 13:03:53 GMT, Daniel Lundén <dlunden at openjdk.org> wrote:

> This changeset adds a flag `StressMacroExpansion` which randomizes macro expansion ordering for stress testing purposes.
> 
> Changes:
> - Implement the flag `StressMacroExpansion`.
> - Add functionality tests for `StressMacroExpansion`, analogous to testing for previous stress flags such as `StressIGVN`.
> - Add `StressMacroExpansion` to a number of tests that already turn on all other stress flags (and therefore should also use `StressMacroExpansion`).
> - Rename the previous compiler phase `MACRO_EXPANSION` to `AFTER_MACRO_EXPANSION`.
> - Add new Ideal phases related to macro expansion, allowing `StressMacroExpansion` testing. Below is a sample phase list screenshot including some of the new phases (IGV print level 4).
>    <p align="center">
>       <img src="https://github.com/openjdk/jdk/assets/4222397/b65c67a0-13f7-45a6-aef4-5dfe259dab66" width="300">
>    </p>
> 
> 
> Question for the review: are the new macro expansion Ideal phases OK, or should we change anything?
> 
> Testing:
> - [GitHub Actions](https://github.com/dlunde/jdk/actions/runs/7756242938)
> - 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.

Looks good to me, modulo Christian's comments. Regarding whether to randomize macro node elimination, I find it a bit confusing that `PhaseMacroExpand` also eliminates macro nodes, perhaps it would be better to, in a separate RFE, split the phase into `PhaseMacroEliminate` and `PhaseMacroExpand`, and introduce a separate `StressMacroElimination` option and new phase names for the former?

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

PR Review: https://git.openjdk.org/jdk/pull/17684#pullrequestreview-1863049642