[jdk11u-dev] RFR: 8275610: C2: Object field load floats above its null check resulting in a segfault

[Goetz Lindenmaier]

I backport this for parity with 11.0.15-oracle.

I had to adapt the test.
@key randomness is not supported in 11, as are -XX:StressSeed=42 and -XX:+StressIGVN.
I removed these.  This makes the second @run call superfluous.

Still, the test crashes the VM without the fix.

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Commit messages:
 - Backport 7c6f57fcb1f1fcecf26f7b8046a5a41ca6d9c315

Changes: https://git.openjdk.java.net/jdk11u-dev/pull/784/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk11u-dev&pr=784&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8275610
  Stats: 110 lines in 2 files changed: 110 ins; 0 del; 0 mod
  Patch: https://git.openjdk.java.net/jdk11u-dev/pull/784.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk11u-dev pull/784/head:pull/784

PR: https://git.openjdk.java.net/jdk11u-dev/pull/784