RFR: JDK-8319784: VM crash during heap dump after JDK-8287061 [v3]

[Cesar Soares Lucas]

> This fixes an incorrect assert in `debugInfo.hpp`. The assert is incorrect because this method may be called before rematerialization of the ObjectValue takes place, and therefore, `_selected` will be nullptr. This pull request patches the method to just return `Handle() => nullptr` if the rematerialization of the object hasn't taken place yet. This is the same behavior used by scalar-replaced objects not participating in merges.
> 
> I added a test to reproduce a scenario where the assert was causing a problem.
> 
> Tested on Ubuntu/MacOS/Windows x86_64 tier1-4.

Cesar Soares Lucas has updated the pull request incrementally with one additional commit since the last revision:

  Update test/hotspot/jtreg/compiler/c2/TestReduceAllocationAndHeapDump.java
  
  Co-authored-by: Aleksey Shipilëv <shipilev at amazon.de>

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/16622/files
  - new: https://git.openjdk.org/jdk/pull/16622/files/26f7c936..43856812

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=16622&range=02
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=16622&range=01-02

  Stats: 1 line in 1 file changed: 0 ins; 0 del; 1 mod
  Patch: https://git.openjdk.org/jdk/pull/16622.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/16622/head:pull/16622

PR: https://git.openjdk.org/jdk/pull/16622