Relax too-strict assert(VM_Version::supports_evex()) in Assembler::locate_operand()

When running on a machine for which we downgrade to UseAVX=2, the InternalErrorTest will run into the assert:

# Internal Error (/home/admin/src/openjdk/jdk/src/hotspot/cpu/x86/assembler_x86.cpp:1092), pid=1199167, tid=1199188
# assert(VM_Version::supports_evex()) failed: shouldn't have EVEX prefix

This happens because memset (which InternalErrorTest ends up calling) *does* use AVX512F instructions, but the decoder doesn't expect it at the SIGBUS site in memset, because we downgrade UseAVX to 2 in vm_version_x86.cpp:

  if (FLAG_IS_DEFAULT(UseAVX)) {
    // Don't use AVX-512 on older Skylakes unless explicitly requested.
    if (use_avx_limit > 2 && is_intel_skylake() && _stepping < 5) {
      FLAG_SET_DEFAULT(UseAVX, 2);
    } else {
      FLAG_SET_DEFAULT(UseAVX, use_avx_limit);
    }
  }

Caused by, or related to JDK-JDK-8320886.

Full stack is:
#
# A fatal error has been detected by the Java Runtime Environment:
#
# Internal Error (/home/admin/src/openjdk/jdk/src/hotspot/cpu/x86/assembler_x86.cpp:1092), pid=1199167, tid=1199188
# assert(VM_Version::supports_evex()) failed: shouldn't have EVEX prefix
#
# JRE version: OpenJDK Runtime Environment (23.0) (slowdebug build 23-internal-adhoc.admin.jdk)
# Java VM: OpenJDK 64-Bit Server VM (slowdebug 23-internal-adhoc.admin.jdk, mixed mode, sharing, tiered, compressed oops, compressed class ptrs, serial gc, linux-amd64)
# Problematic frame:
# V [libjvm.so+0x6a24be] Assembler::locate_operand(unsigned char*, Assembler::WhichOperand)+0xa02
#
# No core dump will be written. Core dumps have been disabled. To enable core dumping, try "ulimit -c unlimited" before starting Java again
#
# If you would like to submit a bug report, please visit:
# https://bugreport.java.com/bugreport/crash.jsp
#
 
--------------- S U M M A R Y ------------
 
Command Line: -Dtest.vm.opts=-XX:MaxRAMPercentage=1.38889 -Dtest.boot.jdk=/usr/lib/jvm/java-21-amazon-corretto -Djava.io.tmpdir=/home/admin/src/openjdk/jdk/build/linux-x86_64-server-slowdebug/test-support/jtreg_test_hotspot_jtreg_runtime_Unsafe_InternalErrorTest_java/tmp -XX:+UseSerialGC -XX:+UnlockExperimentalVMOptions -XX:+UseCompressorFullGC -Dtest.tool.vm.opts=-J-XX:MaxRAMPercentage=1.38889 -J-Dtest.boot.jdk=/usr/lib/jvm/java-21-amazon-corretto -J-Djava.io.tmpdir=/home/admin/src/openjdk/jdk/build/linux-x86_64-server-slowdebug/test-support/jtreg_test_hotspot_jtreg_runtime_Unsafe_InternalErrorTest_java/tmp -J-XX:+UseSerialGC -J-XX:+UnlockExperimentalVMOptions -J-XX:+UseCompressorFullGC -Dtest.compiler.opts= -Dtest.java.opts= -Dtest.jdk=/home/admin/src/openjdk/jdk/build/linux-x86_64-server-slowdebug/images/jdk -Dcompile.jdk=/home/admin/src/openjdk/jdk/build/linux-x86_64-server-slowdebug/images/jdk -Dtest.timeout.factor=4.0 -Dtest.nativepath=/home/admin/src/openjdk/jdk/build/linux-x86_64-server-slowdebug/images/test/hotspot/jtreg/native -Dtest.root=/home/admin/src/openjdk/jdk/test/hotspot/jtreg -Dtest.name=runtime/Unsafe/InternalErrorTest.java -Dtest.file=/home/admin/src/openjdk/jdk/test/hotspot/jtreg/runtime/Unsafe/InternalErrorTest.java -Dtest.src=/home/admin/src/openjdk/jdk/test/hotspot/jtreg/runtime/Unsafe -Dtest.src.path=/home/admin/src/openjdk/jdk/test/hotspot/jtreg/runtime/Unsafe:/home/admin/src/openjdk/jdk/test/lib -Dtest.classes=/home/admin/src/openjdk/jdk/build/linux-x86_64-server-slowdebug/test-support/jtreg_test_hotspot_jtreg_runtime_Unsafe_InternalErrorTest_java/classes/0/runtime/Unsafe/InternalErrorTest.d -Dtest.class.path=/home/admin/src/openjdk/jdk/build/linux-x86_64-server-slowdebug/test-support/jtreg_test_hotspot_jtreg_runtime_Unsafe_InternalErrorTest_java/classes/0/runtime/Unsafe/InternalErrorTest.d:/home/admin/src/openjdk/jdk/build/linux-x86_64-server-slowdebug/test-support/jtreg_test_hotspot_jtreg_runtime_Unsafe_InternalErrorTest_java/classes/0/test/lib -Dtest.class.path.prefix=/home/admin/src/openjdk/jdk/build/linux-x86_64-server-slowdebug/test-support/jtreg_test_hotspot_jtreg_runtime_Unsafe_InternalErrorTest_java/classes/0/runtime/Unsafe/InternalErrorTest.d:/home/admin/src/openjdk/jdk/test/hotspot/jtreg/runtime/Unsafe:/home/admin/src/openjdk/jdk/build/linux-x86_64-server-slowdebug/test-support/jtreg_test_hotspot_jtreg_runtime_Unsafe_InternalErrorTest_java/classes/0/test/lib -Dtest.modules=java.base/jdk.internal.misc java.base/java.nio:+open --add-modules=java.base --add-exports=java.base/jdk.internal.misc=ALL-UNNAMED --add-exports=java.base/java.nio=ALL-UNNAMED --add-opens=java.base/java.nio=ALL-UNNAMED -XX:MaxRAMPercentage=1.38889 -Dtest.boot.jdk=/usr/lib/jvm/java-21-amazon-corretto -Djava.io.tmpdir=/home/admin/src/openjdk/jdk/build/linux-x86_64-server-slowdebug/test-support/jtreg_test_hotspot_jtreg_runtime_Unsafe_InternalErrorTest_java/tmp -XX:+UseSerialGC -XX:+UnlockExperimentalVMOptions -XX:+UseCompressorFullGC -Djava.library.path=/home/admin/src/openjdk/jdk/build/linux-x86_64-server-slowdebug/images/test/hotspot/jtreg/native -XX:CompileCommand=exclude,*InternalErrorTest.main -XX:CompileCommand=inline,*.get -XX:CompileCommand=inline,*Unsafe.* -Xbootclasspath/a:. -XX:+UnlockDiagnosticVMOptions -XX:+WhiteBoxAPI com.sun.javatest.regtest.agent.MainWrapper /home/admin/src/openjdk/jdk/build/linux-x86_64-server-slowdebug/test-support/jtreg_test_hotspot_jtreg_runtime_Unsafe_InternalErrorTest_java/runtime/Unsafe/InternalErrorTest.d/main.0.jta
 
Host: ip-172-31-26-233, Intel(R) Xeon(R) Platinum 8124M CPU @ 3.00GHz, 36 cores, 68G, Debian GNU/Linux 12 (bookworm)
Time: Thu Jan 25 18:42:54 2024 UTC elapsed time: 1.737131 seconds (0d 0h 0m 1s)
 
--------------- T H R E A D ---------------
 
Current thread (0x00007faa9829b0b0): JavaThread "MainThread" [_thread_in_vm, id=1199188, stack(0x00007faa9e4e5000,0x00007faa9e5e5000) (1024K)]
 
Stack: [0x00007faa9e4e5000,0x00007faa9e5e5000], sp=0x00007faa9e5e2060, free space=1012k
Native frames: (J=compiled Java code, j=interpreted, Vv=VM code, C=native code)
V [libjvm.so+0x6a24be] Assembler::locate_operand(unsigned char*, Assembler::WhichOperand)+0xa02 (assembler_x86.cpp:1092)
V [libjvm.so+0x6a2911] Assembler::locate_next_instruction(unsigned char*)+0x1d (assembler_x86.cpp:1243)
V [libjvm.so+0x1378727] PosixSignals::pd_hotspot_signal_handler(int, siginfo_t*, ucontext_t*, JavaThread*)+0x31d (os_linux_x86.cpp:320)
V [libjvm.so+0x155649a] JVM_handle_linux_signal+0x429 (signals_posix.cpp:645)
V [libjvm.so+0x155655b] javaSignalHandler(int, siginfo_t*, void*)+0x2a (signals_posix.cpp:668)
C [libc.so.6+0x3bfd0]
V [libjvm.so+0x991c11] Copy::fill_to_bytes(void*, unsigned long, unsigned char)+0x2c (copy.hpp:278)
V [libjvm.so+0xa5ced7] Copy::fill_to_memory_atomic(void*, unsigned long, unsigned char)+0x159 (copy.cpp:255)
V [libjvm.so+0x16dac7f] Unsafe_SetMemory0+0xf4 (unsafe.cpp:395)
j jdk.internal.misc.Unsafe.setMemory0(Ljava/lang/Object;JJB)V+0 java.base@23-internal
j jdk.internal.misc.Unsafe.setMemory(Ljava/lang/Object;JJB)V+25 java.base@23-internal
j jdk.internal.misc.ScopedMemoryAccess.setMemoryInternal(Ljdk/internal/foreign/MemorySessionImpl;Ljava/lang/Object;JJB)V+17 java.base@23-internal
j jdk.internal.misc.ScopedMemoryAccess.setMemory(Ljdk/internal/foreign/MemorySessionImpl;Ljava/lang/Object;JJB)V+8 java.base@23-internal
j jdk.internal.foreign.AbstractMemorySegmentImpl.fill(B)Ljava/lang/foreign/MemorySegment;+30 java.base@23-internal
j InternalErrorTest.test(Ljava/nio/MappedByteBuffer;Ljdk/internal/misc/Unsafe;JJI)V+105
j InternalErrorTest.main([Ljava/lang/String;)V+231
j java.lang.invoke.LambdaForm$DMH+0x00007faa40002800.invokeStatic(Ljava/lang/Object;Ljava/lang/Object;)V+10 java.base@23-internal
j java.lang.invoke.LambdaForm$MH+0x00007faa40003c00.invoke(Ljava/lang/Object;Ljava/lang/Object;Ljava/lang/Object;)Ljava/lang/Object;+33 java.base@23-internal
j java.lang.invoke.Invokers$Holder.invokeExact_MT(Ljava/lang/Object;Ljava/lang/Object;Ljava/lang/Object;Ljava/lang/Object;)Ljava/lang/Object;+20 java.base@23-internal
j jdk.internal.reflect.DirectMethodHandleAccessor.invokeImpl(Ljava/lang/Object;[Ljava/lang/Object;)Ljava/lang/Object;+55 java.base@23-internal
j jdk.internal.reflect.DirectMethodHandleAccessor.invoke(Ljava/lang/Object;[Ljava/lang/Object;)Ljava/lang/Object;+23 java.base@23-internal
j java.lang.reflect.Method.invoke(Ljava/lang/Object;[Ljava/lang/Object;)Ljava/lang/Object;+102 java.base@23-internal
j com.sun.javatest.regtest.agent.MainWrapper$MainTask.run()V+134
j java.lang.Thread.runWith(Ljava/lang/Object;Ljava/lang/Runnable;)V+5 java.base@23-internal
j java.lang.Thread.run()V+19 java.base@23-internal
v ~StubRoutines::call_stub 0x00007faa87c17d21
V [libjvm.so+0xe416c8] JavaCalls::call_helper(JavaValue*, methodHandle const&, JavaCallArguments*, JavaThread*)+0x634 (javaCalls.cpp:415)
V [libjvm.so+0x1374b00] os::os_exception_wrapper(void (*)(JavaValue*, methodHandle const&, JavaCallArguments*, JavaThread*), JavaValue*, methodHandle const&, JavaCallArguments*, JavaThread*)+0x36 (os_linux.cpp:4903)
V [libjvm.so+0xe41091] JavaCalls::call(JavaValue*, methodHandle const&, JavaCallArguments*, JavaThread*)+0x3d (javaCalls.cpp:329)
V [libjvm.so+0xe400ce] JavaCalls::call_virtual(JavaValue*, Klass*, Symbol*, Symbol*, JavaCallArguments*, JavaThread*)+0x1ba (javaCalls.cpp:185)
V [libjvm.so+0xe401d7] JavaCalls::call_virtual(JavaValue*, Handle, Klass*, Symbol*, Symbol*, JavaThread*)+0x95 (javaCalls.cpp:191)
V [libjvm.so+0xf83f28] thread_entry(JavaThread*, JavaThread*)+0x8e (jvm.cpp:2937)
V [libjvm.so+0xe5bf74] JavaThread::thread_main_inner()+0x168 (javaThread.cpp:721)
V [libjvm.so+0xe5be09] JavaThread::run()+0x1d7 (javaThread.cpp:706)
V [libjvm.so+0x1696cc1] Thread::call_run()+0x1b9 (thread.cpp:221)
V [libjvm.so+0x136a9b0] thread_native_entry(Thread*)+0x1cb (os_linux.cpp:789)
Java frames: (J=compiled Java code, j=interpreted, Vv=VM code)
j jdk.internal.misc.Unsafe.setMemory0(Ljava/lang/Object;JJB)V+0 java.base@23-internal