Running the following test:

make run-test TEST=compiler/loopopts/TestVerifyLoopOptimizations.java TEST_VM_OPTS="-XX:+UseShenandoahGC"

fails with:

# Internal Error (/home/admin/src/openjdk/jdk/src/hotspot/share/opto/loopnode.hpp:470), pid=2362836, tid=2362881
# assert(cle != nullptr) failed: loopexit is null

Current CompileTask:
C2:18095 3693 b 4 java.lang.invoke.LambdaMetafactory::metafactory (71 bytes)

Stack: [0x0000fffee79e6000,0x0000fffee7be4000], sp=0x0000fffee7bde510, free space=2017k
Native frames: (J=compiled Java code, j=interpreted, Vv=VM code, C=native code)
V [libjvm.so+0x11e7a94] IdealLoopTree::verify_tree(IdealLoopTree*) const+0x6d4 (loopnode.hpp:470)
V [libjvm.so+0x11e78a8] IdealLoopTree::verify_tree(IdealLoopTree*) const+0x4e8 (loopnode.cpp:5149)
V [libjvm.so+0x11ea728] PhaseIdealLoop::verify() const+0x2d8 (loopnode.cpp:4926)
V [libjvm.so+0x11eb30c] PhaseIdealLoop::build_and_optimize()+0xa4c (loopnode.cpp:4725)
V [libjvm.so+0x930094] PhaseIdealLoop::optimize(PhaseIterGVN&, LoopOptsMode)+0x304 (loopnode.hpp:1115)
V [libjvm.so+0x929b5c] Compile::optimize_loops(PhaseIterGVN&, LoopOptsMode)+0x68 (compile.cpp:2189)
V [libjvm.so+0x1653c94] ShenandoahBarrierC2Support::expand(Compile*, PhaseIterGVN&)+0xd0 (shenandoahSupport.cpp:58)
V [libjvm.so+0x1582554] ShenandoahBarrierSetC2::expand_barriers(Compile*, PhaseIterGVN&) const+0x14 (shenandoahBarrierSetC2.cpp:750)
V [libjvm.so+0x92ba7c] Compile::Optimize()+0xcdc (compile.cpp:2465)
V [libjvm.so+0x92e75c] Compile::Compile(ciEnv*, ciMethod*, int, Options, DirectiveSet*)+0x15a8 (compile.cpp:861)
V [libjvm.so+0x77a838] C2Compiler::compile_method(ciEnv*, ciMethod*, int, bool, DirectiveSet*)+0x174 (c2compiler.cpp:142)
V [libjvm.so+0x93b364] CompileBroker::invoke_compiler_on_method(CompileTask*)+0xab0 (compileBroker.cpp:2305)
V [libjvm.so+0x93bf74] CompileBroker::compiler_thread_loop()+0x634 (compileBroker.cpp:1964)
V [libjvm.so+0xdf3f70] JavaThread::thread_main_inner()+0xec (javaThread.cpp:721)
V [libjvm.so+0x179d104] Thread::call_run()+0xb0 (thread.cpp:221)
V [libjvm.so+0x13debb8] thread_native_entry(Thread*)+0x138 (os_linux.cpp:864)

It only seems to happen with Shenandoah, not with other GCs. Also, I can easily reproduce the problem on linux-x86_64 and linux-aarch64, but not on macosx-aarch64.

The assert seems to have started occuring with JDK-8309622, but I don't think this is the root cause of the problem.