The attached fuzzer test fails with the following assertion.

To reproduce:
$ java -Xmx1G -Xcomp -Xbatch -XX:-TieredCompilation -XX:CompileOnly=Test Test.java

#
# A fatal error has been detected by the Java Runtime Environment:
#
#  Internal Error (/home/christian/jdk/open/src/hotspot/share/opto/loopTransform.cpp:1263), pid=23631, tid=23643
#  assert(skeleton_predicate_has_opaque(iff)) failed: unexpected
#
# JRE version: Java(TM) SE Runtime Environment (16.0) (slowdebug build 16-internal+0-2020-09-25-1122319.christian...)
# Java VM: Java HotSpot(TM) 64-Bit Server VM (slowdebug 16-internal+0-2020-09-25-1122319.christian..., compiled mode, compressed oops, g1 gc, linux-amd64)
# Problematic frame:
# V  [libjvm.so+0xd143f5]  PhaseIdealLoop::copy_skeleton_predicates_to_main_loop_helper(Node*, Node*, Node*, IdealLoopTree*, LoopNode*, unsigned int, unsigned int, unsigned int, Node*, Node*, Node_List const&)+0x3b5
..........
Command Line: -Xmx1G -Xcomp -Xbatch -XX:-TieredCompilation -XX:CompileOnly=Test --add-modules=ALL-DEFAULT jdk.compiler/com.sun.tools.javac.launcher.Main Test.java
..........
Current thread (0x00007fc5bc335fa0):  JavaThread "C2 CompilerThread0" daemon [_thread_in_native, id=23643, stack(0x00007fc59f1cd000,0x00007fc59f2ce000)]


Current CompileTask:
C2:   9432   90   !b        Test::mainTest (512 bytes)

Stack: [0x00007fc59f1cd000,0x00007fc59f2ce000],  sp=0x00007fc59f2c7d30,  free space=1003k
Native frames: (J=compiled Java code, A=aot compiled Java code, j=interpreted, Vv=VM code, C=native code)
V  [libjvm.so+0xd143f5]  PhaseIdealLoop::copy_skeleton_predicates_to_main_loop_helper(Node*, Node*, Node*, IdealLoopTree*, LoopNode*, unsigned int, unsigned int, unsigned int, Node*, Node*, Node_List const&)+0x3b5
V  [libjvm.so+0xd15145]  PhaseIdealLoop::copy_skeleton_predicates_to_main_loop(CountedLoopNode*, Node*, Node*, IdealLoopTree*, LoopNode*, unsigned int, unsigned int, unsigned int, Node*, Node*, Node_List const&)+0x107
V  [libjvm.so+0xd15e3c]  PhaseIdealLoop::insert_pre_post_loops(IdealLoopTree*, Node_List&, bool)+0xcb6
V  [libjvm.so+0xd1dd6c]  IdealLoopTree::iteration_split_impl(PhaseIdealLoop*, Node_List&)+0x388
V  [libjvm.so+0xd1e001]  IdealLoopTree::iteration_split(PhaseIdealLoop*, Node_List&)+0x10b
V  [libjvm.so+0xd1e09f]  IdealLoopTree::iteration_split(PhaseIdealLoop*, Node_List&)+0x1a9
V  [libjvm.so+0xd1df32]  IdealLoopTree::iteration_split(PhaseIdealLoop*, Node_List&)+0x3c
V  [libjvm.so+0xd1e09f]  IdealLoopTree::iteration_split(PhaseIdealLoop*, Node_List&)+0x1a9
V  [libjvm.so+0xd1e09f]  IdealLoopTree::iteration_split(PhaseIdealLoop*, Node_List&)+0x1a9
V  [libjvm.so+0xd1e09f]  IdealLoopTree::iteration_split(PhaseIdealLoop*, Node_List&)+0x1a9
V  [libjvm.so+0xd1e09f]  IdealLoopTree::iteration_split(PhaseIdealLoop*, Node_List&)+0x1a9
V  [libjvm.so+0xd3138e]  PhaseIdealLoop::build_and_optimize(LoopOptsMode)+0x1470
V  [libjvm.so+0x6f8aa7]  PhaseIdealLoop::PhaseIdealLoop(PhaseIterGVN&, LoopOptsMode)+0xb3
V  [libjvm.so+0x6f8ba2]  PhaseIdealLoop::optimize(PhaseIterGVN&, LoopOptsMode)+0x46
V  [libjvm.so+0x6ec785]  Compile::optimize_loops(PhaseIterGVN&, LoopOptsMode)+0xf7
V  [libjvm.so+0x6ed533]  Compile::Optimize()+0xc0b
V  [libjvm.so+0x6e67d8]  Compile::Compile(ciEnv*, ciMethod*, int, bool, bool, bool, bool, DirectiveSet*)+0x1090
V  [libjvm.so+0x5e12a9]  C2Compiler::compile_method(ciEnv*, ciMethod*, int, bool, DirectiveSet*)+0x15b
V  [libjvm.so+0x701859]  CompileBroker::invoke_compiler_on_method(CompileTask*)+0x895
V  [libjvm.so+0x7004df]  CompileBroker::compiler_thread_loop()+0x3df
V  [libjvm.so+0x10c508f]  compiler_thread_entry(JavaThread*, Thread*)+0x69
V  [libjvm.so+0x10c035a]  JavaThread::thread_main_inner()+0x14c
V  [libjvm.so+0x10c0206]  JavaThread::run()+0x118
V  [libjvm.so+0x10bc35a]  Thread::call_run()+0x180
V  [libjvm.so+0xec5db6]  thread_native_entry(Thread*)+0x1e4