On linux86_64 fastdebug, with ubsan enabled, we run into this issue :

  assert(_type != end_marker, "already at end");

/jdk/src/hotspot/share/code/dependencies.cpp:906:3: runtime error: load of value 4294967295, which is not a valid value for type 'DepType'
    #0 0x14e2c941db7b in Dependencies::DepStream::next() /jdk/src/hotspot/share/code/dependencies.cpp:906
    #1 0x14e2cadaf907 in Dependencies::validate_dependencies(CompileTask*, char**) /jdk/src/hotspot/share/code/dependencies.cpp:632
    #2 0x14e2ca7b70c0 in ciEnv::validate_compile_task_dependencies(ciMethod*) /jdk/src/hotspot/share/ci/ciEnv.cpp:1007
    #3 0x14e2ca7c1719 in ciEnv::register_method(ciMethod*, int, CodeOffsets*, int, CodeBuffer*, int, OopMapSet*, ExceptionHandlerTable*, ImplicitExceptionTable*, AbstractCompiler*, bool, bool, bool, int, RTMState) /jdk/src/hotspot/share/ci/ciEnv.cpp:1091
    #4 0x14e2ca2744f6 in Compilation::install_code(int) /jdk/src/hotspot/share/c1/c1_Compilation.cpp:426
    #5 0x14e2ca283a81 in Compilation::compile_method() /jdk/src/hotspot/share/c1/c1_Compilation.cpp:488
    #6 0x14e2ca2854aa in Compilation::Compilation(AbstractCompiler*, ciEnv*, ciMethod*, int, BufferBlob*, bool, DirectiveSet*) /jdk/src/hotspot/share/c1/c1_Compilation.cpp:609
    #7 0x14e2ca28a9f3 in Compiler::compile_method(ciEnv*, ciMethod*, int, bool, DirectiveSet*) /jdk/src/hotspot/share/c1/c1_Compiler.cpp:260
    #8 0x14e2cab51df1 in CompileBroker::invoke_compiler_on_method(CompileTask*) /jdk/src/hotspot/share/compiler/compileBroker.cpp:2303
    #9 0x14e2cab538ee in CompileBroker::compiler_thread_loop() /jdk/src/hotspot/share/compiler/compileBroker.cpp:1961
    #10 0x14e2cb7b03dc in JavaThread::thread_main_inner() /jdk/src/hotspot/share/runtime/javaThread.cpp:759
    #11 0x14e2cd2a7c2f in Thread::call_run() /jdk/src/hotspot/share/runtime/thread.cpp:225
    #12 0x14e2cc791415 in thread_native_entry /jdk/src/hotspot/os/linux/os_linux.cpp:846
    #13 0x14e2d2d486e9 in start_thread (/lib64/libpthread.so.0+0xa6e9) (BuildId: 2f8d3c2d0f4d7888c2598d2ff6356537f5708a73)
   ... (rest of output omitted)

Looks like some variable (probably _type) is not initialized or somehow overwritten.
We might also remove the assertion if it brings not much benefit.