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

[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.

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

Changes: https://git.openjdk.java.net/jdk/pull/1078/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=1078&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8255598
  Stats: 2 lines in 1 file changed: 1 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