RFR: 8296155: Simplify CDS heap region address calculation [v2]

[Ioi Lam]

On Tue, 1 Nov 2022 21:51:58 GMT, Coleen Phillimore <coleenp at openjdk.org> wrote:

>> src/hotspot/share/cds/filemap.cpp line 1558:
>> 
>>> 1556:   _is_bitmap_region = (region_index == MetaspaceShared::bm);
>>> 1557: 
>>> 1558:   if (_is_heap_region) {
>> 
>> Explain please.  Only heap region has a non-null dumptime base?
>
> ie add a comment here too.

I added comments here. There are also comments in cds.h that explains what these fields should be for different types of regions.

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PR: https://git.openjdk.org/jdk/pull/10923