[BACKOUT] Generational ZGC: Tests crash with assert(index == 0 || is_power_of_2(index))

The following test failed in the JDK22 CI:

java/lang/template/StringTemplateTest.java

Here's a snippet from the log file:

#section:main
----------messages:(6/261)----------
command: main StringTemplateTest
reason: Assumed action based on file name: run main StringTemplateTest
started: Fri Aug 25 12:57:01 UTC 2023
Mode: othervm [test requires --enable-preview]
finished: Fri Aug 25 12:59:30 UTC 2023
elapsed time (seconds): 148.189
----------configuration:(0/0)----------
----------System.out:(19/1829)----------
#
# A fatal error has been detected by the Java Runtime Environment:
#
# Internal Error (/opt/mach5/mesos/work_dir/slaves/cd627e65-f015-4fb1-a1d2-b6c9b8127f98-S140300/frameworks/1735e8a2-a1db-478c-8104-60c8b0af87dd-0196/executors/21307581-dc30-4aac-89c4-4bfbb5641d9a/runs/73c33e79-93ed-483f-ad32-d91e0813fc35/workspace/open/src/hotspot/share/opto/arraycopynode.cpp:140), pid=2882412, tid=2882708
# assert((get_length_if_constant(phase) == -1) != ary_src->size()->is_con() || phase->is_IterGVN() || phase->C->inlining_incrementally() || StressReflectiveCode) failed: inconsistent
#
# JRE version: Java(TM) SE Runtime Environment (22.0+13) (fastdebug build 22-ea+13-893)
# Java VM: Java HotSpot(TM) 64-Bit Server VM (fastdebug 22-ea+13-893, mixed mode, sharing, tiered, compressed oops, compressed class ptrs, g1 gc, linux-aarch64)
# Problematic frame:
# V [libjvm.so+0x5cb858][thread 2882454 also had an error]
  ArrayCopyNode::get_count(PhaseGVN*) const+0x318
#
# Core dump will be written. Default location: Core dumps may be processed with "/opt/core.sh %p" (or dumping to /opt/mach5/mesos/work_dir/slaves/cd627e65-f015-4fb1-a1d2-b6c9b8127f98-S140206/frameworks/1735e8a2-a1db-478c-8104-60c8b0af87dd-0196/executors/e6c933b5-0f70-447c-b126-cecc796d8682/runs/691795a7-a726-4d41-acc4-49f2e7e22c06/testoutput/test-support/jtreg_open_test_jdk_tier1/scratch/3_1/core.2882412)
#
# An error report file with more information is saved as:
# /opt/mach5/mesos/work_dir/slaves/cd627e65-f015-4fb1-a1d2-b6c9b8127f98-S140206/frameworks/1735e8a2-a1db-478c-8104-60c8b0af87dd-0196/executors/e6c933b5-0f70-447c-b126-cecc796d8682/runs/691795a7-a726-4d41-acc4-49f2e7e22c06/testoutput/test-support/jtreg_open_test_jdk_tier1/scratch/3_1/hs_err_pid2882412.log

------ Timeout during error reporting after 120 s. ------
# [ timer expired, abort... ]
----------System.err:(2/117)----------
Note: StringTemplateTest$.java uses preview features of Java SE 22.
Note: Recompile with -Xlint:preview for details.
----------rerun:(39/5906)*----------


Here's the crashing thread's stack:

--------------- T H R E A D ---------------

Current thread (0x0000ffff326d21d0): JavaThread "C2 CompilerThread1" daemon [_thread_in_native, id=2882708, stack(0x0000ffff5c27f000,0x0000ffff5c47d000) (2040K)]


Current CompileTask:
C2: 17957 4785 4 java.lang.invoke.StringConcatFactory::makeConcatWithTemplate (645 bytes)

Stack: [0x0000ffff5c27f000,0x0000ffff5c47d000], sp=0x0000ffff5c478310, free space=2020k
Native frames: (J=compiled Java code, j=interpreted, Vv=VM code, C=native code)
V [libjvm.so+0x5cb858] ArrayCopyNode::get_count(PhaseGVN*) const+0x318 (arraycopynode.cpp:140)
V [libjvm.so+0x5d0d54] ArrayCopyNode::Ideal(PhaseGVN*, bool)+0x100 (arraycopynode.cpp:560)
V [libjvm.so+0x13eb318] PhaseGVN::transform_no_reclaim(Node*)+0x88 (phaseX.cpp:667)
V [libjvm.so+0x5f39c8] BarrierSetC2::clone(GraphKit*, Node*, Node*, Node*, bool) const+0x1f4 (barrierSetC2.cpp:692)
V [libjvm.so+0x787910] CardTableBarrierSetC2::clone(GraphKit*, Node*, Node*, Node*, bool) const+0x2c (cardTableBarrierSetC2.cpp:129)
V [libjvm.so+0x10e7ee0] LibraryCallKit::copy_to_clone(Node*, Node*, Node*, bool)+0x180 (library_call.cpp:4935)
V [libjvm.so+0x10f7ec0] LibraryCallKit::inline_native_clone(bool)+0x840 (library_call.cpp:5058)
V [libjvm.so+0x1106b90] LibraryIntrinsic::generate(JVMState*)+0x17c (library_call.cpp:118)
V [libjvm.so+0xa7f96c] Parse::do_call()+0x58c (doCall.cpp:675)
V [libjvm.so+0x13c3ea8] Parse::do_one_bytecode()+0x4d8 (parse2.cpp:2728)
V [libjvm.so+0x13b389c] Parse::do_one_block()+0x59c (parse1.cpp:1577)
V [libjvm.so+0x13b47f0] Parse::do_all_blocks()+0x150 (parse1.cpp:713)
V [libjvm.so+0x13b8958] Parse::Parse(JVMState*, ciMethod*, float)+0xa38 (parse1.cpp:617)
V [libjvm.so+0x75e768] ParseGenerator::generate(JVMState*)+0x168 (callGenerator.cpp:99)
V [libjvm.so+0xa7f96c] Parse::do_call()+0x58c (doCall.cpp:675)
V [libjvm.so+0x13c3ea8] Parse::do_one_bytecode()+0x4d8 (parse2.cpp:2728)
V [libjvm.so+0x13b389c] Parse::do_one_block()+0x59c (parse1.cpp:1577)
V [libjvm.so+0x13b47f0] Parse::do_all_blocks()+0x150 (parse1.cpp:713)
V [libjvm.so+0x13b8958] Parse::Parse(JVMState*, ciMethod*, float)+0xa38 (parse1.cpp:617)
V [libjvm.so+0x75e768] ParseGenerator::generate(JVMState*)+0x168 (callGenerator.cpp:99)
V [libjvm.so+0x904b9c] Compile::Compile(ciEnv*, ciMethod*, int, Options, DirectiveSet*)+0xfdc (compile.cpp:779)
V [libjvm.so+0x75c3b0] C2Compiler::compile_method(ciEnv*, ciMethod*, int, bool, DirectiveSet*)+0x110 (c2compiler.cpp:119)
V [libjvm.so+0x911044] CompileBroker::invoke_compiler_on_method(CompileTask*)+0x8e4 (compileBroker.cpp:2276)
V [libjvm.so+0x911a74] CompileBroker::compiler_thread_loop()+0x594 (compileBroker.cpp:1944)
V [libjvm.so+0xdaaa7c] JavaThread::thread_main_inner()+0xec (javaThread.cpp:720)
V [libjvm.so+0x160c084] Thread::call_run()+0xb0 (thread.cpp:220)
V [libjvm.so+0x1365978] thread_native_entry(Thread*)+0x138 (os_linux.cpp:784)
C [libpthread.so.0+0x7908] start_thread+0x188