RFR: 8372162: G1: Merge subclasses of G1IHOPControl into parent class

[Albert Mingkun Yang]

On Wed, 19 Nov 2025 15:12:39 GMT, Albert Mingkun Yang <ayang at openjdk.org> wrote:

> Merging two subclasses into the parent class to simplify type hierarchy. The internal `bool` flag doesn't introduce much complexity; instead, improves readability, IMO.
> 
> Perf neutral on linux-x64/aarch64: cachestree, dacapo, dacapo23, specjbb2005, specjbb2015, specjvm2008.
> 
> Test: tier1-5

Thanks for review.

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PR Comment: https://git.openjdk.org/jdk/pull/28391#issuecomment-3563112941