RFR: 8288537: Move Devirtualizer out of hotspot/share/memory/iterator.hpp [v3]

[Coleen Phillimore]

On Fri, 17 Jun 2022 15:13:57 GMT, Ioi Lam <iklam at openjdk.org> wrote:

>> HotSpot build time has regressed quite a bit since JDK 17 (1m46s vs 2m20s on my machine). Now it's time to do some header file cleanup.
>> 
>> iterator.hpp contains a hodge-podge of unrelated classes. Some of these classes have dependencies on other headers (e.g., `Devirtualizer` depends on bitMap.hpp) that slow down C++ compilation.
>> 
>> This patch moves two infrequently used classes, `Devirtualizer` and `SerializeClosure`, to their own header files. This reduces the total number of C++ lines compiled for libjvm.so for about 1%.
>
> Ioi Lam has updated the pull request incrementally with one additional commit since the last revision:
> 
>   renamed include guard macro

Looks like an improvement.

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Marked as reviewed by coleenp (Reviewer).

PR: https://git.openjdk.org/jdk/pull/9176