compiler/stable/TestUnstableStable.java starts to fail after JDK-8372700 when run with --enable-preview:

#
# A fatal error has been detected by the Java Runtime Environment:
#
# Internal Error (/opt/mach5/mesos/work_dir/slaves/da1065b5-7b94-4f0d-85e9-a3a252b9a32e-S35745/frameworks/1735e8a2-a1db-478c-8104-60c8b0af87dd-0196/executors/762852bd-74e2-45bd-95e5-127f3bccd51f/runs/0b086b23-db0b-48e0-a47c-17873cab58dc/workspace/open/src/hotspot/share/ci/ciObject.hpp:161), pid=767934, tid=767955
# assert(is_instance()) failed: bad cast
#
# JRE version: Java(TM) SE Runtime Environment (27.0+1) (fastdebug build 27-valhalla+1-38)
# Java VM: Java HotSpot(TM) 64-Bit Server VM (fastdebug 27-valhalla+1-38, mixed mode, sharing, compressed oops, compressed class ptrs, g1 gc, linux-amd64)
# Problematic frame:
# V [libjvm.so+0xab7d18] ciFlatArray::field_value(int, ciField*)+0x4c8
..........
C2:136 54 b compiler.stable.TestUnstableStable::testArray0 (14 bytes)

Stack: [0x00007ff267f00000,0x00007ff268000000], sp=0x00007ff267ffae10, free space=1003k
Native frames: (J=compiled Java code, j=interpreted, Vv=VM code, C=native code)
V [libjvm.so+0xab7d18] ciFlatArray::field_value(int, ciField*)+0x4c8 (ciObject.hpp:161)
V [libjvm.so+0x1d2dd10] Type::make_constant_from_array_element(ciArray*, int, int, int, BasicType, bool)+0x50
V [libjvm.so+0x17b3ae5] LoadNode::Value(PhaseGVN*) const+0x205
V [libjvm.so+0x1997e9e] PhaseIterGVN::transform_old(Node*)+0x36e
V [libjvm.so+0x199ca35] PhaseIterGVN::optimize()+0xc5
V [libjvm.so+0xc18555] Compile::Optimize()+0x775
V [libjvm.so+0xc1bb3d] Compile::Compile(ciEnv*, ciMethod*, int, Options, DirectiveSet*)+0x1d8d
V [libjvm.so+0xa0a925] C2Compiler::compile_method(ciEnv*, ciMethod*, int, bool, DirectiveSet*)+0x4b5
V [libjvm.so+0xc2b480] CompileBroker::invoke_compiler_on_method(CompileTask*)+0x780
V [libjvm.so+0xc2cce0] CompileBroker::compiler_thread_loop()+0x530
V [libjvm.so+0x11f38cb] JavaThread::thread_main_inner()+0x13b
V [libjvm.so+0x1ce2246] Thread::call_run()+0xb6
V [libjvm.so+0x18f8358] thread_native_entry(Thread*)+0x118