[jdk8u-dev] RFR: 8250825: C2 crashes with assert(field != __null) failed: missing field [v2]

[SendaoYan]

> Hi all,
> This is backport of [JDK-8250825](https://bugs.openjdk.org/browse/JDK-8250825). It's prefixed PR for [JDK-8255466](https://bugs.openjdk.org/browse/JDK-8255466) [backport](https://github.com/openjdk/jdk8u-dev/pull/536).
> New test fails without the patch, passes with it.
> 
> There are two parts make this backport not clean:
> 
> 1. Patch does not apply cleanly due to different context, before [JDK-8250825](https://bugs.openjdk.org/browse/JDK-8250825)  the  PR [JDK-8230505](https://bugs.openjdk.org/browse/JDK-8230505) change releated lines, and I think [JDK-8230505](https://bugs.openjdk.org/browse/JDK-8230505) do not needed backport to jdk8u-dev.
> 2. The added testcase can't backport to jdk8u directly, `import jdk.internal.misc.Unsafe` should instead of `import sun.misc.Unsafe` in jdk8u.
> 
> 
> 
> Additional testing:
> 
> - [ ] linux x64 tier1/2/3 jtreg test
> - [ ] inux aarch64 tier1/2/3 jtreg test

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

  implement Unsafe.getUnsafe() in jdk8u

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

Changes:
  - all: https://git.openjdk.org/jdk8u-dev/pull/552/files
  - new: https://git.openjdk.org/jdk8u-dev/pull/552/files/7f528207..f0bba3ee

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk8u-dev&pr=552&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk8u-dev&pr=552&range=00-01

  Stats: 12 lines in 1 file changed: 10 ins; 0 del; 2 mod
  Patch: https://git.openjdk.org/jdk8u-dev/pull/552.diff
  Fetch: git fetch https://git.openjdk.org/jdk8u-dev.git pull/552/head:pull/552

PR: https://git.openjdk.org/jdk8u-dev/pull/552