The following test failed in the JDK16 CI:

runtime/cds/appcds/cacheObject/CheckCachedMirrorTest.java

Here's a snippet from the log file:

----------stdout:(21/1714)----------
# To suppress the following error report, specify this argument
# after -XX: or in .hotspotrc: SuppressErrorAt=/type.hpp:667
#
# A fatal error has been detected by the Java Runtime Environment:
#
# Internal Error (/System/Volumes/Data/mesos/work_dir/slaves/4076d11c-c6ed-4d07-84c1-4ab8d55cd975-S435659/frameworks/1735e8a2-a1db-478c-8104-60c8b0af87dd-0196/executors/58150fc4-7bd5-4707-bc8f-021d0c4034b8/runs/b6a18f16-f9fa-4fec-bf90-a6320f6cec14/workspace/open/src/hotspot/share/opto/type.hpp:667), pid=12219, tid=22531
# assert(i < _cnt) failed: oob
#
# JRE version: Java(TM) SE Runtime Environment (16.0+21) (fastdebug build 16-ea+21-1133)
# Java VM: Java HotSpot(TM) 64-Bit Server VM (fastdebug 16-ea+21-1133, mixed mode, tiered, compressed oops, g1 gc, bsd-amd64)
# Core dump will be written. Default location: core.12219
#
# An error report file with more information is saved as:
# /System/Volumes/Data/mesos/work_dir/slaves/4076d11c-c6ed-4d07-84c1-4ab8d55cd975-S443996/frameworks/1735e8a2-a1db-478c-8104-60c8b0af87dd-0196/executors/42426cde-5b61-4992-a481-016c331fecdf/runs/af1b5403-0ccf-45ed-93c6-6ade25ee2115/testoutput/test-support/jtreg_open_test_hotspot_jtreg_hotspot_tier2_runtime/scratch/0/hs_err_pid12219.log
#
# Compiler replay data is saved as:
# /System/Volumes/Data/mesos/work_dir/slaves/4076d11c-c6ed-4d07-84c1-4ab8d55cd975-S443996/frameworks/1735e8a2-a1db-478c-8104-60c8b0af87dd-0196/executors/42426cde-5b61-4992-a481-016c331fecdf/runs/af1b5403-0ccf-45ed-93c6-6ade25ee2115/testoutput/test-support/jtreg_open_test_hotspot_jtreg_hotspot_tier2_runtime/scratch/0/replay_pid12219.log
#
# If you would like to submit a bug report, please visit:
# https://bugreport.java.com/bugreport/crash.jsp
#
result: Error. Agent communication error: java.io.EOFException; check console log for any additional details

Here's the crashing thread's stack:

--------------- T H R E A D ---------------

Current thread (0x00007fa1e1855820): JavaThread "C2 CompilerThread0" daemon [_thread_in_native, id=22531, stack(0x0000700007ca0000,0x0000700007da0000)]


Current CompileTask:
C2: 256615 9032 4 com.sun.tools.javac.parser.JavacParser::classOrInterfaceOrRecordBodyDeclaration (994 bytes)

Stack: [0x0000700007ca0000,0x0000700007da0000], sp=0x0000700007d9be30, free space=1007k
Native frames: (J=compiled Java code, A=aot compiled Java code, j=interpreted, Vv=VM code, C=native code)
V [libjvm.dylib+0x11639c5] VMError::report_and_die(int, char const*, char const*, __va_list_tag*, Thread*, unsigned char*, void*, void*, char const*, int, unsigned long)+0x6d5
V [libjvm.dylib+0x11640fb] VMError::report_and_die(Thread*, void*, char const*, int, char const*, char const*, __va_list_tag*)+0x3b
V [libjvm.dylib+0x61d24f] report_vm_error(char const*, int, char const*, char const*, ...)+0x13f
V [libjvm.dylib+0xe0c4d0] ProjNode::proj_type(Type const*) const+0xb0
V [libjvm.dylib+0xed1c05] PhaseIterGVN::transform_old(Node*)+0x385
V [libjvm.dylib+0xed1466] PhaseIterGVN::optimize()+0x246
V [libjvm.dylib+0x5c9020] Compile::remove_speculative_types(PhaseIterGVN&)+0x4c0
V [libjvm.dylib+0x5c243d] Compile::Optimize()+0x50d
V [libjvm.dylib+0x5c047c] Compile::Compile(ciEnv*, ciMethod*, int, bool, bool, bool, bool, DirectiveSet*)+0x140c
V [libjvm.dylib+0x4b5b90] C2Compiler::compile_method(ciEnv*, ciMethod*, int, bool, DirectiveSet*)+0x1d0
V [libjvm.dylib+0x5dc318] CompileBroker::invoke_compiler_on_method(CompileTask*)+0x608
V [libjvm.dylib+0x5dbaa6] CompileBroker::compiler_thread_loop()+0x2e6
V [libjvm.dylib+0x10bcd24] JavaThread::thread_main_inner()+0x2b4
V [libjvm.dylib+0x10b84e7] Thread::call_run()+0x1b7
V [libjvm.dylib+0xe74f2f] thread_native_entry(Thread*)+0x15f
C [libsystem_pthread.dylib+0x6109] _pthread_start+0x94
C [libsystem_pthread.dylib+0x1b8b] thread_start+0xf