This is an intermittent failure. Run the test with -XX:-UseCompressedOops -XX:-UseCompressedClassPointers, I manage to trigger it in the 5th scenario (id4) once every 100 runs.

Note: The hs_err file below was run with a slightly modified VM in which I tried to print more info of the assert.

# A fatal error has been detected by the Java Runtime Environment:
#
# Internal Error (/home/merykitty/openjdk/valhalla/src/hotspot/share/opto/chaitin.hpp:161), pid=708893, tid=708909
# Error: assert(false) failed
#
# JRE version: OpenJDK Runtime Environment (27.0) (slowdebug build 27-internal-adhoc.merykitty.valhalla)
# Java VM: OpenJDK 64-Bit Server VM (slowdebug 27-internal-adhoc.merykitty.valhalla, mixed mode, tiered, g1 gc, linux-amd64)
# Problematic frame:
# V [libjvm.so+0xa37ea9] LRG::set_num_regs(int)+0x9f

Current CompileTask:
C2:29481 1657 b 4 compiler.valhalla.inlinetypes.TestArrays::test31 (67 bytes)

Stack: [0x00007e80181fc000,0x00007e80182fc000], sp=0x00007e80182f7930, free space=1006k
Native frames: (J=compiled Java code, j=interpreted, Vv=VM code, C=native code)
V [libjvm.so+0xa37ea9] LRG::set_num_regs(int)+0x9f (chaitin.hpp:161)
V [libjvm.so+0xa2c16f] PhaseChaitin::gather_lrg_masks(bool)+0x7ad
V [libjvm.so+0xa2a42d] PhaseChaitin::Register_Allocate()+0x789
V [libjvm.so+0xb5691a] Compile::Code_Gen()+0x662
V [libjvm.so+0xb46fa8] Compile::Compile(ciEnv*, ciMethod*, int, Options, DirectiveSet*)+0x1b66
V [libjvm.so+0x9c5b0a] C2Compiler::compile_method(ciEnv*, ciMethod*, int, bool, DirectiveSet*)+0x4cc
V [libjvm.so+0xb74da9] CompileBroker::invoke_compiler_on_method(CompileTask*)+0xdc3
V [libjvm.so+0xb731cc] CompileBroker::compiler_thread_loop()+0x57a
V [libjvm.so+0xb97e8b] CompilerThread::thread_entry(JavaThread*, JavaThread*)+0x8d
V [libjvm.so+0x10ffa9a] JavaThread::thread_main_inner()+0x1ca
V [libjvm.so+0x10ff8cd] JavaThread::run()+0x1e7
V [libjvm.so+0x1c140c3] Thread::call_run()+0x1bd
V [libjvm.so+0x1747753] thread_native_entry(Thread*)+0x1bd