(synopsis is provisional, please feel free to change it as you see fit)

$ CONF=macosx-aarch64-server-fastdebug make test TEST=jdk/jfr/threading/TestManyVirtualThreads.java TEST_VM_OPTS=-XX:+UseShenandoahGC

# SIGSEGV (0xb) at pc=0x000000010304ab28, pid=47888, tid=43011
#
# JRE version: OpenJDK Runtime Environment (24.0) (fastdebug build 24-internal-adhoc.shipilev.shipilev-jdk)
# Java VM: OpenJDK 64-Bit Server VM (fastdebug 24-internal-adhoc.shipilev.shipilev-jdk, mixed mode, sharing, tiered, compressed oops, compressed class ptrs, shenandoah gc, bsd-aarch64)
# Problematic frame:
# V [libjvm.dylib+0xc66b28] PhaseIdealLoop::set_ctrl(Node*, Node*)+0x60

Current CompileTask:
C2:1378 1214 ! 4 jdk.internal.vm.Continuation::enter (19 bytes)

Stack: [0x0000000172398000,0x000000017259b000], sp=0x0000000172596ca0, free space=2043k
Native frames: (J=compiled Java code, j=interpreted, Vv=VM code, C=native code)
V [libjvm.dylib+0xc66b28] PhaseIdealLoop::set_ctrl(Node*, Node*)+0x60
V [libjvm.dylib+0x1086e10] PhaseIdealLoop::register_new_node(Node*, Node*)+0x64
V [libjvm.dylib+0x1063164] ShenandoahBarrierC2Support::pin_and_expand(PhaseIdealLoop*)+0x884
V [libjvm.dylib+0xfba0a4] ShenandoahBarrierSetC2::optimize_loops(PhaseIdealLoop*, LoopOptsMode, VectorSet&, Node_Stack&, Node_List&) const+0x4c
V [libjvm.dylib+0xca27e4] PhaseIdealLoop::build_and_optimize()+0x934
V [libjvm.dylib+0x4e6ed8] PhaseIdealLoop::PhaseIdealLoop(PhaseIterGVN&, LoopOptsMode)+0x180
V [libjvm.dylib+0x4d97a4] PhaseIdealLoop::optimize(PhaseIterGVN&, LoopOptsMode)+0x6c
V [libjvm.dylib+0x105b9a4] ShenandoahBarrierC2Support::expand(Compile*, PhaseIterGVN&)+0x5c
V [libjvm.dylib+0xfba04c] ShenandoahBarrierSetC2::expand_barriers(Compile*, PhaseIterGVN&) const+0x14
V [libjvm.dylib+0x4d29f0] Compile::Optimize()+0xbac
V [libjvm.dylib+0x4d0a48] Compile::Compile(ciEnv*, ciMethod*, int, Options, DirectiveSet*)+0x13bc
V [libjvm.dylib+0x3949b4] C2Compiler::compile_method(ciEnv*, ciMethod*, int, bool, DirectiveSet*)+0x1e4
V [libjvm.dylib+0x4efc2c] CompileBroker::invoke_compiler_on_method(CompileTask*)+0x9a8
V [libjvm.dylib+0x4eef14] CompileBroker::compiler_thread_loop()+0x340
V [libjvm.dylib+0x8b98b4] JavaThread::thread_main_inner()+0x1c8
V [libjvm.dylib+0x8b9450] JavaThread::run()+0x368
V [libjvm.dylib+0x11933a8] Thread::call_run()+0xf0
V [libjvm.dylib+0xe4ba64] thread_native_entry(Thread*)+0x138
C [libsystem_pthread.dylib+0x6f94] _pthread_start+0x88

siginfo: si_signo: 11 (SIGSEGV), si_code: 2 (SEGV_ACCERR), si_addr: 0x000000000000001c