RFR (M): 8199742: Clean up state flags in G1CollectorState

[Thomas Schatzl]

Hi all,

  I would like to request reviews for this change that cleans up the
flags in G1CollectorState, applying uniform naming, removing members
that were basically temporary variables for a single method, and remove
redundant flags (the four flags in the "XXX" block were basically a
single one).

While this is just a step towards my goal of removing the flags as much
as possible and merging them into enums, I think this is a very
worthwhile step on that way. Further it blocks a few more changes of
mine :P

Naming guidelines:
  - flags indicating a particular GC were named "in_XXX_gc"
  - durations spanning multiple garbage collections, i.e. phases have
the "phase" postfix.

Other than that there were general updates for the names to hopefully
make them reflect reality a bit closer.

Main changes apart from naming were

- in g1CollectionSet.cpp where I made  add_young_region_common() to not
update statistics. This avoids the need to make the full gc also a
young gc (at least as far as flags are concerned); to fix this properly
we would need to know the previous phase we were in when coming into
the full gc. I just do not think it is worth adding a new state here
(and the code has been wrong previously too, unconditionally adding
these statistics to the young-only phase).

I made a note in the follow-up change JDK-8080226.

- the changes in G1Policy::record_collection_pause_end() were mostly
due to removing the last_gc_was_young() member which was basically a
reminder just for this method that the current gc was a young-only gc.

There is still _initiate_conc_mark_if_possible flag that indicates that
a state change to initial mark should occur asap, but I think that
should be moved to e.g. g1policy in a next change.

CR:
https://bugs.openjdk.java.net/browse/JDK-8199742
Webrev:
http://cr.openjdk.java.net/~tschatzl/8199742/webrev
Testing:
hs-tier 1-5

These changes are based on the rebuild remembered sets concurrently
changes. As it may be a bit of work to get them working (I already
pushed to first four), here is a webrev that updates latest jdk/hs to
that level at http://cr.openjdk.java.net/~tschatzl/8199742/baseline/web
rev/

Thanks,
  Thomas