The following assertion was hit by runthese testing in JDK12-24 ATR testing:

#
# A fatal error has been detected by the Java Runtime Environment:
#
# Internal Error (t:/workspace/open/src/hotspot/share/opto/split_if.cpp:322), pid=33176, tid=40244
# assert(prior_n->is_Region()) failed: must be a post-dominating merge point
#
# JRE version: Java(TM) SE Runtime Environment (12.0+24) (fastdebug build 12-ea+24)
# Java VM: Java HotSpot(TM) 64-Bit Server VM (fastdebug 12-ea+24, mixed mode, sharing, tiered, compressed oops, parallel gc, windows-amd64)
# Core dump will be written. Default location: T:\testOutput\test-support\jtreg_closed_test_hotspot_jtreg_applications_runthese_RunThese30M_java\scratch\0\hs_err_pid33176.mdmp
#
# If you would like to submit a bug report, please visit:
# http://bugreport.java.com/bugreport/crash.jsp
#

--------------- S U M M A R Y ------------

Command Line: -XX:MaxRAMPercentage=8 -XX:+UseParallelGC -XX:+UseParallelOldGC -XX:+UseNUMA -XX:+IgnoreUnrecognizedVMOptions --add-opens=java.base/java.net=ALL-UNNAMED -Dseed=4189835214713881 -XX:MaxRAMPercentage=50 applications.runthese.Runner -duration 30 -runlist T:\testOutput\test-support\jtreg_closed_test_hotspot_jtreg_applications_runthese_RunThese30M_java\scratch\0\.\RunTheseTestList.dat

Host: sca00mgr, Intel(R) Xeon(R) CPU E5-2690 0 @ 2.90GHz, 6 cores, 30G, Windows Server 2012 R2 , 64 bit Build 9600 (6.3.9600.17415)
Time: Sun Dec 16 07:36:47 2018 Ame elapsed time: 195 seconds (0d 0h 3m 15s)

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

Current thread (0x00000087f35ad800): JavaThread "C2 CompilerThread0" daemon [_thread_in_native, id=40244, stack(0x00000087f4ed0000,0x00000087f4fd0000)]


Current CompileTask:
C2: 195431 32218 4 jdk.internal.module.Checks::isJavaIdentifier (76 bytes)

Stack: [0x00000087f4ed0000,0x00000087f4fd0000]
Native frames: (J=compiled Java code, j=interpreted, Vv=VM code, C=native code)
V [jvm.dll+0xb58ee1] os::platform_print_native_stack+0xf1 (os_windows_x86.cpp:369)
V [jvm.dll+0xd77310] VMError::report+0xe80 (vmerror.cpp:698)
V [jvm.dll+0xd78b64] VMError::report_and_die+0x854 (vmerror.cpp:1471)
V [jvm.dll+0xd79224] VMError::report_and_die+0x64 (vmerror.cpp:1295)
V [jvm.dll+0x57e3fe] report_vm_error+0x7e (debug.cpp:232)
V [jvm.dll+0xc4ef90] PhaseIdealLoop::spinup+0x2e0 (split_if.cpp:322)
V [jvm.dll+0xc4efe4] PhaseIdealLoop::spinup+0x334 (split_if.cpp:328)
V [jvm.dll+0xc4eae5] PhaseIdealLoop::handle_use+0x1d5 (split_if.cpp:419)
V [jvm.dll+0xc4e5b4] PhaseIdealLoop::do_split_if+0xe14 (split_if.cpp:546)
V [jvm.dll+0xa0991d] PhaseIdealLoop::split_if_with_blocks_post+0x69d (loopopts.cpp:1304)
V [jvm.dll+0xa09247] PhaseIdealLoop::split_if_with_blocks+0x1d7 (loopopts.cpp:1491)
V [jvm.dll+0x9e7139] PhaseIdealLoop::build_and_optimize+0xeb9 (loopnode.cpp:2969)
V [jvm.dll+0x511ee7] Compile::optimize_loops+0x157 (compile.cpp:2180)
V [jvm.dll+0x505df8] Compile::Optimize+0x1498 (compile.cpp:2362)
V [jvm.dll+0x501fa2] Compile::Compile+0xed2 (compile.cpp:871)
V [jvm.dll+0x3fe2fb] C2Compiler::compile_method+0x10b (c2compiler.cpp:112)
V [jvm.dll+0x51ccf9] CompileBroker::invoke_compiler_on_method+0x729 (compilebroker.cpp:2123)
V [jvm.dll+0x51ac79] CompileBroker::compiler_thread_loop+0x309 (compilebroker.cpp:1808)
V [jvm.dll+0xd1be71] JavaThread::run+0x2c1 (thread.cpp:1792)
V [jvm.dll+0xd10b8b] Thread::call_run+0x21b (thread.cpp:394)
V [jvm.dll+0xb57783] thread_native_entry+0x123 (os_windows.cpp:459)
C [ucrtbase.DLL+0x1d885]
C [KERNEL32.DLL+0x13d2]
C [ntdll.dll+0x154f4]