JDK-8361608 : C2: assert(opaq->outcnt() == 1 && opaq->in(1) == limit) failed
  • Type: Bug
  • Component: hotspot
  • Sub-Component: compiler
  • Affected Version: 26
  • Priority: P3
  • Status: Open
  • Resolution: Unresolved
  • Submitted: 2025-07-08
  • Updated: 2025-07-21
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JDK 26
26Unresolved
Related Reports
Relates :  
JDK-8355488 - Add stress mode for C2 loop peeling
Description
The attached Java Fuzzer test fails with the following assertion by using the new StressLoopPeeling flag (probably just revealed an existing issue that is not a recent regression, please add the affected versions accordingly once the root cause is known):

To reproduce (needs RepeatCompilation since it fails intermittently):
$ java -XX:CompileCommand=compileonly,Test::test -XX:-TieredCompilation -Xbatch -XX:+StressLoopPeeling -XX:PerMethodTrapLimit=0 -XX:CompileCommand=RepeatCompilation,*Test*::test,100 Test.java
$ java -XX:CompileCommand=compileonly,Reduced::test -XX:-TieredCompilation -Xbatch -XX:+StressLoopPeeling -XX:PerMethodTrapLimit=0 -XX:CompileCommand=RepeatCompilation,*Reduced*::test,100 Reduced.java

#
# A fatal error has been detected by the Java Runtime Environment:
#
#  Internal Error (c:\sb\prod\1751821445\workspace\open\src\hotspot\share\opto\loopTransform.cpp:1889), pid=19420, tid=35996
#  Error: assert(opaq->outcnt() == 1 && opaq->in(1) == limit) failed
#
# JRE version: Java(TM) SE Runtime Environment (26.0+6) (fastdebug build 26-ea+6-494)
# Java VM: Java HotSpot(TM) 64-Bit Server VM (fastdebug 26-ea+6-494, mixed mode, sharing, compressed oops, compressed class ptrs, g1 gc, windows-amd64)
# Problematic frame:
# V  [jvm.dll+0xc3e72d]  PhaseIdealLoop::do_unroll+0x115d
..........
Command Line: -XX:+UnlockDiagnosticVMOptions -XX:RepeatCompilation=99 -Xmx1G -XX:+IgnoreUnrecognizedVMOptions -XX:CompileCommand=quiet -XX:CompileCommand=compileonly,*Test*::* -XX:-TieredCompilation -Xbatch -XX:+UnlockDiagnosticVMOptions -XX:+StressLCM -XX:+StressGCM -XX:+StressIGVN -XX:+StressCCP -XX:+StressMacroExpansion -XX:+StressLoopPeeling -XX:+UnlockExperimentalVMOptions -XX:PerMethodSpecTrapLimit=0 -XX:PerMethodTrapLimit=0 -XX:MaxRAMPercentage=4.16667 -Dtest.boot.jdk=c:\ade\mesos\work_dir\jib-master\install\jdk\24\36\bundles\windows-x64\jdk-24_windows-x64_bin.zip\jdk-24 -Djava.io.tmpdir=c:\sb\prod\1751956893\testoutput\test-support\jtreg_closed_test_hotspot_jtreg_applications_javafuzzer_LongRunningTests_java\tmp -XX:+CreateCoredumpOnCrash Test
............
C2:5058    3 %  b        Test::bMeth @ 50 (277 bytes)

Stack: [0x000000b581e00000,0x000000b581f00000],  sp=0x000000b581efb300,  free space=1004k
Native frames: (J=compiled Java code, j=interpreted, Vv=VM code, C=native code)
V  [jvm.dll+0xc3e72d]  PhaseIdealLoop::do_unroll+0x115d  (loopTransform.cpp:1889)
V  [jvm.dll+0xc44a65]  IdealLoopTree::iteration_split_impl+0x685  (loopTransform.cpp:3516)
V  [jvm.dll+0xc44318]  IdealLoopTree::iteration_split+0x118  (loopTransform.cpp:3540)
V  [jvm.dll+0xc44234]  IdealLoopTree::iteration_split+0x34  (loopTransform.cpp:3524)
V  [jvm.dll+0xc44390]  IdealLoopTree::iteration_split+0x190  (loopTransform.cpp:3552)
V  [jvm.dll+0xc44390]  IdealLoopTree::iteration_split+0x190  (loopTransform.cpp:3552)
V  [jvm.dll+0xc44390]  IdealLoopTree::iteration_split+0x190  (loopTransform.cpp:3552)
V  [jvm.dll+0xc44390]  IdealLoopTree::iteration_split+0x190  (loopTransform.cpp:3552)
V  [jvm.dll+0xc44390]  IdealLoopTree::iteration_split+0x190  (loopTransform.cpp:3552)
V  [jvm.dll+0xc44390]  IdealLoopTree::iteration_split+0x190  (loopTransform.cpp:3552)
V  [jvm.dll+0xc44390]  IdealLoopTree::iteration_split+0x190  (loopTransform.cpp:3552)
V  [jvm.dll+0xc51b3e]  PhaseIdealLoop::build_and_optimize+0x103e  (loopnode.cpp:5019)
V  [jvm.dll+0x5c841b]  Compile::Optimize+0xbbb  (compile.cpp:2503)
V  [jvm.dll+0x5c5181]  Compile::Compile+0x10e1  (compile.cpp:860)
V  [jvm.dll+0x4c8e59]  C2Compiler::compile_method+0x179  (c2compiler.cpp:144)
V  [jvm.dll+0x5e36f4]  CompileBroker::invoke_compiler_on_method+0x804  (compileBroker.cpp:2336)
V  [jvm.dll+0x5e09ef]  CompileBroker::compiler_thread_loop+0x32f  (compileBroker.cpp:1972)
V  [jvm.dll+0x936df8]  JavaThread::thread_main_inner+0x288  (javaThread.cpp:774)
V  [jvm.dll+0x1044a02]  Thread::call_run+0x1b2  (thread.cpp:248)
V  [jvm.dll+0xdf6e21]  thread_native_entry+0xe1  (os_windows.cpp:562)
C  [ucrtbase.dll+0x2268a]  (no source info available)
C  [KERNEL32.DLL+0x17ac4]  (no source info available)
C  [ntdll.dll+0x5a8c1]  (no source info available)
Comments
ILW = Assertion failure during loop unrolling, single fuzzer test with StressLoopPeeling, disable compilation of affected method = HLM = P3
08-07-2025