NPE on tiered compilation only (seeking help to narrow it down)

[Dawid Weiss]

Hello,

Uwe Schindler (CC) has been trying to narrow down a Lucene bug which
manifests itself on recent hotspot builds and results in odd NPEs. It
looks very strange -- similar to what I reported a while ago (and
thought to have been fixed by JDK-8060036).

The problem is that an NPE starts to appear at numerous places after
the JVM warms up a bit during a test run. What is odd is that:

1. it happens on 32 bit and 64 bit JVMs (32 bit is easier to reproduce),
2. it does *not* happen with -client,
3. it does happen with -server,
4. it does *not* seem to happen with -server and -XX:-TieredCompilation....

I am a bit lost about (4) and (3) -- both these should end up in C2
being used (with -server using tiered compilation). Is there any way
we can turn something on or off to narrow the scope there? What's
going on during tiered compilation that can be causing this?

Dawid