8256536: Newer AMD 19h (EPYC) Processor family defaults

Reviewed-by: kvn

src/hotspot/cpu/x86/vm_version_x86.cpp

@@ -1311,9 +1311,10 @@ void VM_Version::get_processor_features() {
     }
 #endif // COMPILER2
 
-    // Some defaults for AMD family 17h || Hygon family 18h
-    if (cpu_family() == 0x17 || cpu_family() == 0x18) {
-      // On family 17h processors use XMM and UnalignedLoadStores for Array Copy
+    // Some defaults for AMD family >= 17h && Hygon family 18h
+    if (cpu_family() >= 0x17) {
+      // On family >=17h processors use XMM and UnalignedLoadStores
+      // for Array Copy
       if (supports_sse2() && FLAG_IS_DEFAULT(UseXMMForArrayCopy)) {
         FLAG_SET_DEFAULT(UseXMMForArrayCopy, true);
       }
@@ -1519,6 +1520,14 @@ void VM_Version::get_processor_features() {
     FLAG_SET_DEFAULT(UseFastStosb, false);
   }
 
+  // For AMD Processors use XMM/YMM MOVDQU instructions
+  // for Object Initialization as default
+  if (is_amd() && cpu_family() >= 0x19) {
+    if (FLAG_IS_DEFAULT(UseFastStosb)) {
+      UseFastStosb = false;
+    }
+  }
+
   // Use XMM/YMM MOVDQU instruction for Object Initialization
   if (!UseFastStosb && UseSSE >= 2 && UseUnalignedLoadStores) {
     if (FLAG_IS_DEFAULT(UseXMMForObjInit)) {