[lworld] RFR: 8367553: [lworld] compiler/valhalla/inlinetypes/TestNullableArrays.java fails with segfault in C1 compiled code on aarch64

[Marc Chevalier]

Seems that it was just [JDK-8367151: [lworld] CorrectlyRestoreRfp.java triggers "bad oop found" during deoptimization](https://bugs.openjdk.org/browse/JDK-8367151)/https://github.com/openjdk/valhalla/pull/1751. When I checked first if it still reproduces, https://github.com/openjdk/valhalla/pull/1751 wasn't integrated yet. And after investigation, it turned out to be the same issue. And after integration of the said PR, the problem didn't show again under much more extensive testing than what was enough to reproduce before.

In more details, the case I investigated was mostly in `test76_verifier` (occasionally in `test78_verifier`)
https://github.com/openjdk/valhalla/blob/acb511a9f5c7b750b41e1ce77aab3d1a59613097/test/hotspot/jtreg/compiler/valhalla/inlinetypes/TestNullableArrays.java#L2100-L2120

that is C1-compiled. During a call to C2-compiled `verify`:
https://github.com/openjdk/valhalla/blob/acb511a9f5c7b750b41e1ce77aab3d1a59613097/test/hotspot/jtreg/compiler/valhalla/inlinetypes/TestNullableArrays.java#L1145-L1153

an oop is passed in rfp. Sometimes, the GC moves the object during the execution of `verify`, it updated the wrong copy of RFP on the stack. Then `verify` hits an uncommon trap, and in the process picks the wrong `rfp` by exactly the same mechanism as in [JDK-8367151](https://bugs.openjdk.org/browse/JDK-8367151). Later in `test76_verify`, the content of rfp, that now contains a wrong oop, is used, garbage is read, segfault.

The fact that is goes through an uncommon trap makes it a slightly different flavor than what I've seen before. Also, not I should have taken my own advice, and use SerialGC, it would have saved me some complications!

I suggest we just un-problem list now.

Thanks,
Marc

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

Commit messages:
 - un-ProblemList

Changes: https://git.openjdk.org/valhalla/pull/1766/files
  Webrev: https://webrevs.openjdk.org/?repo=valhalla&pr=1766&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8367553
  Stats: 7 lines in 1 file changed: 0 ins; 7 del; 0 mod
  Patch: https://git.openjdk.org/valhalla/pull/1766.diff
  Fetch: git fetch https://git.openjdk.org/valhalla.git pull/1766/head:pull/1766

PR: https://git.openjdk.org/valhalla/pull/1766