C2: assert(n->outcnt() != 0 || C->top() == n || n->is_Proj()) failed: No dead instructions after post-alloc

The attached Java Fuzzer test starts to fail after JDK-8264649 (but seems to just reveal an existing issue) with the following assertion failure:

To reproduce:
$ java -Xmx1G -Xcomp -XX:CompileOnly=Test -XX:-TieredCompilation -XX:+IgnoreUnrecognizedVMOptions -XX:+UnlockDiagnosticVMOptions -XX:+StressLCM -XX:+StressGCM -XX:+StressIGVN -XX:StressSeed=568109485 Test.java
$ java -Xmx1G -Xcomp -XX:CompileOnly=Reduced -XX:-TieredCompilation -XX:+StressLCM -XX:+StressGCM -XX:+StressIGVN -XX:StressSeed=568109485 Reduced.java

#
# A fatal error has been detected by the Java Runtime Environment:
#
# Internal Error (/opt/mach5/mesos/work_dir/slaves/3c846bae-ce30-4a97-93ee-9fef4497ccb6-S79067/frameworks/1735e8a2-a1db-478c-8104-60c8b0af87dd-0196/executors/be546687-12db-4ded-a96b-86062b189919/runs/56ca4e2d-638a-4f38-8b25-3d968f5f0d09/workspace/open/src/hotspot/share/opto/chaitin.cpp:1670), pid=32679, tid=32692
# assert(n->outcnt() != 0 || C->top() == n || n->is_Proj()) failed: No dead instructions after post-alloc
#
# JRE version: Java(TM) SE Runtime Environment (17.0+26) (fastdebug build 17-ea+26-LTS-2439)
# Java VM: Java HotSpot(TM) 64-Bit Server VM (fastdebug 17-ea+26-LTS-2439, compiled mode, sharing, compressed oops, compressed class ptrs, g1 gc, linux-amd64)
# Problematic frame:
# V [libjvm.so+0x8b17b3] PhaseChaitin::fixup_spills()+0x133
...........
Command Line: -Xmx1G -Xcomp -Xbatch -XX:CompileOnly=Test -XX:CompileCommand=quiet -XX:-TieredCompilation -XX:+IgnoreUnrecognizedVMOptions -XX:+UnlockDiagnosticVMOptions -XX:+StressLCM -XX:+StressGCM -XX:+StressIGVN -XX:StressSeed=568109485 Test
...........
Current thread (0x00007fda10480150): JavaThread "C2 CompilerThread0" daemon [_thread_in_native, id=32692, stack(0x00007fda001c7000,0x00007fda002c8000)]


Current CompileTask:
C2: 407 3 !b Test::mainTest (682 bytes)

Stack: [0x00007fda001c7000,0x00007fda002c8000], sp=0x00007fda002c2eb0, free space=1007k
Native frames: (J=compiled Java code, j=interpreted, Vv=VM code, C=native code)
V [libjvm.so+0x8b17b3] PhaseChaitin::fixup_spills()+0x133
V [libjvm.so+0x8bca86] PhaseChaitin::Register_Allocate()+0xa66
V [libjvm.so+0xa1cc77] Compile::Code_Gen()+0x317
V [libjvm.so+0xa2818f] Compile::Compile(ciEnv*, ciMethod*, int, bool, bool, bool, bool, DirectiveSet*)+0x164f
V [libjvm.so+0x84959a] C2Compiler::compile_method(ciEnv*, ciMethod*, int, bool, DirectiveSet*)+0x1ea
V [libjvm.so+0xa38a89] CompileBroker::invoke_compiler_on_method(CompileTask*)+0xfb9
V [libjvm.so+0xa397f8] CompileBroker::compiler_thread_loop()+0x5a8
V [libjvm.so+0x18b2e91] JavaThread::thread_main_inner()+0x271
V [libjvm.so+0x18baa90] Thread::call_run()+0x100
V [libjvm.so+0x15872b4] thread_native_entry(Thread*)+0x104