RFR: 8255598: [PPC64] assert(Universe::heap()->is_in(result)) failed: object not in heap [v2]

[Martin Doerr]

> JDK-8237363 introduced "assert(Universe::heap()->is_in..." check in CompressedOops::decode functions.
> This assertion restricts the usability of the decode functions. There are periods of time (during GC) at which we can't use " Universe::heap()->is_in" because the pointer gets switched between old and new location, but "Universe::heap()->is_in" is not yet accurate.
> PPC64 code has a usage of CompressedOops::decode which is affected by this problem. (It was observed with SerialGC, see JBS.)
> We could also use a weaker assertion, but seems like other people value the stronger assertion more. So I suggest to use decode_raw as workaround for PPC64.

Martin Doerr has updated the pull request incrementally with one additional commit since the last revision:

  add comment and use CompressedOops::is_null

-------------

Changes:
  - all: https://git.openjdk.java.net/jdk/pull/1078/files
  - new: https://git.openjdk.java.net/jdk/pull/1078/files/4ffffa95..400ecfda

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=1078&range=01
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=1078&range=00-01

  Stats: 4 lines in 1 file changed: 3 ins; 0 del; 1 mod
  Patch: https://git.openjdk.java.net/jdk/pull/1078.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/1078/head:pull/1078

PR: https://git.openjdk.java.net/jdk/pull/1078