RFR: Epsilon GC

[Aleksey Shipilev]

Hi,

This is the review thread for Epsilon GC changes.

JEP, targeted to 11:
  http://openjdk.java.net/jeps/318
  (you can find links to binary builds and sandbox locations there)

Webrev:
  http://cr.openjdk.java.net/~shade/epsilon/webrev.05/

Notes:

  *) See how the whole things is _almost_ drop-in to hotspot/share/gc, without having arch-specific
mess -- thanks to GC interface work done over last years;

  *) There are some leftovers due to GC barriers work in progress: templateTable_arm.cpp addition
goes away after JDK-8201786 [1], c1_LIRGenerator.cpp change should go away after C1 barriers
modularization is complete, graphKit.cpp change should go away after C2 barriers modularization is
complete;

  *) Half of the webrev are Epsilon-specific tests. They take ~30s in release and ~60s in fastdebug
on my desktop. They are not in tier1, so smoke testing time is not affected;

  *) UseEpsilonGC is experimental. This should be fine after conditional GC compilation [2], so
vendors who are unwilling to extend whatever small notion [3] of support comes with experimental VM
option, may choose not to build it.

Testing: all platform builds, gc/epsilon on x86_64

Thanks,
-Aleksey

[1] https://bugs.openjdk.java.net/browse/JDK-8201786
[2] https://bugs.openjdk.java.net/browse/JDK-8200729
[3] http://hg.openjdk.java.net/jdk/jdk/file/3661f31c6df4/src/hotspot/share/runtime/globals.hpp#l150

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