RFR (M): 8235860: Obsolete the UseParallelOldGC option

[Kim Barrett]

> On Dec 17, 2019, at 10:51 AM, Thomas Schatzl <thomas.schatzl at oracle.com> wrote:
> 
> Hi all,
> 
>  can I get reviews for this change that implements obsoletion of the UseParallelOldGC option, i.e. removal of the Parallel GC Serial Old collector?
> 
> ((I am counting this as "M" because it's 99% removal of code)
> 
> CR:
> https://bugs.openjdk.java.net/browse/JDK-8235860
> Webrev:
> http://cr.openjdk.java.net/~tschatzl/8235860/webrev/
> Testing:
> hs-tier1-5 almost done
> 
> Thanks,
>  Thomas

Looks good.  One very minor issue and some pre-existing issues with
the block comment before SplitInfo.  That block comment should be
dealt with separately from this change.

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src/hotspot/share/gc/parallel/parallelArguments.cpp
  47   assert(UseParallelGC, "Error");
  48   FLAG_SET_DEFAULT(UseParallelGC, true);

I think line 48 was to account for the possibility that we got here
via +UseParallelOldGC.  It's redundant now.

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src/hotspot/share/gc/parallel/psParallelCompact.hpp
 886 // ...  The permanent generation is

Pre-existing lingering comments about permgen.

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src/hotspot/share/gc/parallel/psParallelCompact.hpp

Pre-existing: It seems like the big block comment before SplitInfo
should have received some updates as part of the recent shadow-region
patch, but it wasn't touched.

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