Reliably happens on x86_32:

$ CONF=linux-x86-server-fastdebug make run-test TEST=serviceability/jvmti/GetLocalVariable/GetLocalVars.java

# Internal Error (/home/shade/trunks/shipilev-jdk18/src/hotspot/share/opto/phaseX.cpp:1741), pid=2708428, tid=2708444
# assert(t->meet(t0) == t) failed: Not monotonic

Current thread (0xa4666478): JavaThread "C2 CompilerThread0" daemon [_thread_in_native, id=2721649, stack(0xa373f000,0xa3800000)]

Current CompileTask:
C2: 5783 1738 b 4 java.util.IdentityHashMap::<init> (44 bytes)

Stack: [0xa373f000,0xa3800000], sp=0xa37fd2f0, free space=760k
Native frames: (J=compiled Java code, j=interpreted, Vv=VM code, C=native code)
V [libjvm.so+0x1393634] PhaseCCP::analyze()+0x484
V [libjvm.so+0x95edc1] Compile::Optimize()+0x931
V [libjvm.so+0x96109a] Compile::Compile(ciEnv*, ciMethod*, int, Options, DirectiveSet*)+0x135a
V [libjvm.so+0x786323] C2Compiler::compile_method(ciEnv*, ciMethod*, int, bool, DirectiveSet*)+0x863
V [libjvm.so+0x97355d] CompileBroker::invoke_compiler_on_method(CompileTask*)+0x15bd
V [libjvm.so+0x974479] CompileBroker::compiler_thread_loop()+0x849
V [libjvm.so+0x99d3fb] CompilerThread::thread_entry(JavaThread*, JavaThread*)+0x2b
V [libjvm.so+0x16d2628] JavaThread::thread_main_inner()+0x5b8
V [libjvm.so+0x16d4bd2] JavaThread::run()+0x382
V [libjvm.so+0x16db4ae] Thread::call_run()+0xfe
V [libjvm.so+0x130d873] thread_native_entry(Thread*)+0x123
C [libpthread.so.0+0x8635] start_thread+0xf5

Bisection points to JDK-8278413.