RFR: 8346552: C2: Add IR tests to check that Parse Predicate cloning in Loop Unswitching works as expected

[Manuel Hässig]

On Mon, 7 Apr 2025 07:49:08 GMT, Manuel Hässig <duke at openjdk.org> wrote:

> # Issue Summary
> 
> When a loop is unswitched, all parse predicates from the original loop must be cloned to the second loop that is created. Forgetting to clone a parse predicate is a common error during development on loop unswitching code that we could not catch previously. Since we have the IR-framework now, this PR introduces a test to catch this error.
> 
> # Changes
> 
> The main contribution of this PR is a test to ensure that all predicates have been cloned into an unswitched loop. This also required some relating changes:
>  - add `OPAQUE_TEMPLATE_ASSERTION_PREDICATE_NODE` to the IR-framework,
>  - add some missing parse predicate nodes to the IR-framework,
>  - change the output of the labels of parse predicate nodes in the ideal graph so they can be recognized reliably by the IR-framework (the main problem was that `Loop ` is a prefix of `Loop Limit Check` that is hard to distinguish with spaces instead of underlines),
>  - rework the regex for detecting parse predicates in the IR-framework,
>  - add a test to ensure parse predicates are cloned into unswitched loops.
> 
> # Testing
> 
> - [Github Actions](https://github.com/mhaessig/jdk/actions/runs/14266369099)
> - tier1 through tier3 plus Oracle internal testing

After some discussion, we decided that we should add before and after loop phases to help with the IR phase matching.

Filed [JDK-8353842](https://bugs.openjdk.org/browse/JDK-8353842)

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PR Comment: https://git.openjdk.org/jdk/pull/24479#issuecomment-2782972982