RFC: Code cache scan should use RESOLVE?

[Aleksey Shipilev]

Hi,

Looking through nightly test failures, this caught my eye:

#  Internal Error
(/opt/jenkins/workspace/jdk9-shenandoah-fastdebug/hotspot/src/share/vm/gc/shenandoah/shenandoahConcurrentMark.inline.hpp:247),
pid=16927, tid=16935
#  assert(oopDesc::unsafe_equals(obj,
ShenandoahBarrierSet::resolve_oop_static(obj))) failed: need to-space object here

V  [libjvm.so+0xa6653a]  report_vm_error(char const*, int, char const*, char
const*, ...)+0xea
V  [libjvm.so+0x143f2d5]  ShenandoahMarkRefsClosure::do_oop(oop*)+0x115
V  [libjvm.so+0x11f1862]  nmethod::oops_do(OopClosure*, bool)+0x542
V  [libjvm.so+0xd74a89]  CodeBlobToOopClosure::do_code_blob(CodeBlob*)+0x29
V  [libjvm.so+0x985523]  CodeCache::blobs_do(CodeBlobClosure*)+0x163
V  [libjvm.so+0x148e03f]  SCMConcurrentMarkingTask::work(unsigned int)+0x1df
V  [libjvm.so+0x16d9225]  GangWorker::loop()+0xc5
V  [libjvm.so+0x1252152]  thread_native_entry(Thread*)+0x112

It seems to me that with ShenandoahConcurrentCodeRoots enabled recently, we are
hitting this path. And oops coming from code roots may be stale, so we need to
RESOLVE them? If so, here's a blind patch:
  http://cr.openjdk.java.net/~shade/shenandoah/codecache-roots-assert/webrev.01/

I was unable to replicate the failure locally, so this is a shot in the dark.

Thanks,
-Aleksey