The lowering of MonitorEnterNode and MonitorExitNode in Graal21 has an issue where it "pushes" more arguments than needed by the callee (monitorenterStub and monitorexitStub, respectively) when JVMCIUseFastLocking is disabled. See Stacktrace of the error below.

Thread[#19,JVMCI-native CompilerThread2,5,main]: Compilation of java.util.concurrent.ConcurrentHashMap.putVal(Object, Object, boolean) @ -1 failed: java.lang.ArrayIndexOutOfBoundsException: Index 3 out of bounds for length 3
at jdk.internal.vm.compiler/org.graalvm.compiler.replacements.SnippetTemplate$Arguments.addConst(SnippetTemplate.java:641)
at jdk.internal.vm.compiler/org.graalvm.compiler.replacements.SnippetTemplate$Arguments.addConst(SnippetTemplate.java:636)
at jdk.internal.vm.compiler/org.graalvm.compiler.hotspot.replacements.MonitorSnippets$Templates.lower(MonitorSnippets.java:911)
at jdk.internal.vm.compiler/org.graalvm.compiler.hotspot.meta.DefaultHotSpotLoweringProvider.lowerWithoutDelegation(DefaultHotSpotLoweringProvider.java:459)
at jdk.internal.vm.compiler/org.graalvm.compiler.hotspot.meta.DefaultHotSpotLoweringProvider.lower(DefaultHotSpotLoweringProvider.java:629)
at jdk.internal.vm.compiler/org.graalvm.compiler.hotspot.amd64.AMD64HotSpotLoweringProvider.lower(AMD64HotSpotLoweringProvider.java:87)
at jdk.internal.vm.compiler/org.graalvm.compiler.nodes.spi.Lowerable.lower(Lowerable.java:40)
at jdk.internal.vm.compiler/org.graalvm.compiler.phases.common.LoweringPhase.process(LoweringPhase.java:665)
at jdk.internal.vm.compiler/org.graalvm.compiler.phases.common.LoweringPhase$ProcessFrame.preprocess(LoweringPhase.java:553)
at jdk.internal.vm.compiler/org.graalvm.compiler.phases.common.LoweringPhase.processBlock(LoweringPhase.java:764)
at jdk.internal.vm.compiler/org.graalvm.compiler.phases.common.LoweringPhase.lower(LoweringPhase.java:297)
at jdk.internal.vm.compiler/org.graalvm.compiler.phases.common.LoweringPhase.run(LoweringPhase.java:271)
at jdk.internal.vm.compiler/org.graalvm.compiler.phases.common.LoweringPhase.run(LoweringPhase.java:113)
at jdk.internal.vm.compiler/org.graalvm.compiler.phases.BasePhase.apply(BasePhase.java:434)
at jdk.internal.vm.compiler/org.graalvm.compiler.phases.BasePhase.apply(BasePhase.java:322)
at jdk.internal.vm.compiler/org.graalvm.compiler.core.phases.BaseTier.run(BaseTier.java:47)
at jdk.internal.vm.compiler/org.graalvm.compiler.phases.BasePhase.apply(BasePhase.java:434)
at jdk.internal.vm.compiler/org.graalvm.compiler.phases.BasePhase.apply(BasePhase.java:322)
at jdk.internal.vm.compiler/org.graalvm.compiler.core.GraalCompiler.emitFrontEnd(GraalCompiler.java:304)
at jdk.internal.vm.compiler/org.graalvm.compiler.core.GraalCompiler.compile(GraalCompiler.java:169)
at jdk.internal.vm.compiler/org.graalvm.compiler.core.GraalCompiler.compileGraph(GraalCompiler.java:137)
at jdk.internal.vm.compiler/org.graalvm.compiler.hotspot.HotSpotGraalCompiler.compileHelper(HotSpotGraalCompiler.java:244)
at jdk.internal.vm.compiler/org.graalvm.compiler.hotspot.HotSpotGraalCompiler.compile(HotSpotGraalCompiler.java:259)
at jdk.internal.vm.compiler/org.graalvm.compiler.hotspot.CompilationTask$HotSpotCompilationWrapper.performCompilation(CompilationTask.java:202)
at jdk.internal.vm.compiler/org.graalvm.compiler.hotspot.CompilationTask$HotSpotCompilationWrapper.performCompilation(CompilationTask.java:108)
at jdk.internal.vm.compiler/org.graalvm.compiler.core.CompilationWrapper.run(CompilationWrapper.java:222)
at jdk.internal.vm.compiler/org.graalvm.compiler.hotspot.CompilationTask.runCompilation(CompilationTask.java:382)
at jdk.internal.vm.compiler/org.graalvm.compiler.hotspot.CompilationTask.runCompilation(CompilationTask.java:357)
at jdk.internal.vm.compiler/org.graalvm.compiler.hotspot.HotSpotGraalCompiler.compileMethod(HotSpotGraalCompiler.java:159)
at jdk.internal.vm.compiler/org.graalvm.compiler.hotspot.HotSpotGraalCompiler.compileMethod(HotSpotGraalCompiler.java:693)
at jdk.internal.vm.compiler/org.graalvm.compiler.hotspot.HotSpotGraalCompiler.compileMethod(HotSpotGraalCompiler.java:110)
at jdk.internal.vm.ci@21.0.6/jdk.vm.ci.hotspot.HotSpotJVMCIRuntime.compileMethod(HotSpotJVMCIRuntime.java:924)