Shenandoah: SIGSEGV crash in unnecessary_acquire due to LoadStore split through phi

Two seperate users on separate systems reported the same issue. Example output (more details in the two hs_err log files):

#
# A fatal error has been detected by the Java Runtime Environment:
#
# SIGSEGV (0xb) at pc=0x0000ffff9825d794, pid=1, tid=16
#
# JRE version: OpenJDK Runtime Environment Temurin-17.0.10+7 (17.0.10+7) (build 17.0.10+7)
# Java VM: OpenJDK 64-Bit Server VM Temurin-17.0.10+7 (17.0.10+7, mixed mode, sharing, tiered, compressed oops, compressed class ptrs, shenandoah gc, linux-aarch64)
# Problematic frame:
# V [libjvm.so+0x2dd794] unnecessary_acquire(Node const*)+0x40
#
# Core dump will be written. Default location: Core dumps may be processed with "/usr/share/apport/apport -p%p -s%s -c%c -d%d -P%P -u%u -g%g -- %E" (or dumping to //core.1)
#
# An error report file with more information is saved as:
# /tmp/hs_err_pid1.log
#
# Compiler replay data is saved as:
# /tmp/replay_pid1.log
#
# If you would like to submit a bug report, please visit:
# https://github.com/adoptium/adoptium-support/issues
#

[error occurred during error reporting (), id 0x5, SIGTRAP (0x5) at pc=0x0000ffff992a71ec]

Current CompileTask:
C2:5753646 53798 4 org.apache.hc.client5.http.impl.async.InternalHttpAsyncExecRuntime::connectEndpoint (99 bytes)

Stack: [0x0000ffffa0936000,0x0000ffffa0b34000], sp=0x0000ffffa0b2f800, free space=2022k
Native frames: (J=compiled Java code, j=interpreted, Vv=VM code, C=native code)
V [libjvm.so+0x2dd794] unnecessary_acquire(Node const*)+0x40
V [libjvm.so+0x642f28] State::DFA(int, Node const*)+0x16b8
V [libjvm.so+0xace2dc] Matcher::Label_Root(Node const*, State*, Node*, Node*&)+0x338
V [libjvm.so+0xacef88] Matcher::match_tree(Node const*)+0xa8
V [libjvm.so+0xad2b54] Matcher::xform(Node*, int)+0x804
V [libjvm.so+0xad574c] Matcher::match()+0x72c
V [libjvm.so+0x5a4854] Compile::Code_Gen()+0xa4
V [libjvm.so+0x5a9648] Compile::Compile(ciEnv*, ciMethod*, int, bool, bool, bool, bool, bool, DirectiveSet*)+0xf88
V [libjvm.so+0x4f02d4] C2Compiler::compile_method(ciEnv*, ciMethod*, int, bool, DirectiveSet*)+0xd0
V [libjvm.so+0x5b174c] CompileBroker::invoke_compiler_on_method(CompileTask*)+0xd18
V [libjvm.so+0x5b21bc] CompileBroker::compiler_thread_loop()+0x4fc
V [libjvm.so+0xd87e70] JavaThread::thread_main_inner()+0x15c
V [libjvm.so+0xd8cec8] Thread::call_run()+0xa8
V [libjvm.so+0xb76b5c] thread_native_entry(Thread*)+0xdc
C [libpthread.so.0+0x77e4] start_thread+0x18c

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Users reported same crashes on 17.0.7 and 17.0.9.

One user upgraded to 21.0.1 and reported no crashes after 48 hours

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Happy to follow up with the OP's for further investigation steps.