8239927: Product variable PrefetchFieldsAhead is unused and should be removed

Reviewed-by: njian, dholmes

Author: Bhavana-Kilambi

src/hotspot/cpu/x86/vm_version_x86.cpp

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 1997, 2021, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 1997, 2022, Oracle and/or its affiliates. All rights reserved.
  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
  *
  * This code is free software; you can redistribute it and/or modify it
@@ -1818,9 +1818,6 @@ void VM_Version::get_processor_features() {
   if (FLAG_IS_DEFAULT(PrefetchScanIntervalInBytes)) {
     FLAG_SET_DEFAULT(PrefetchScanIntervalInBytes, 576);
   }
-  if (FLAG_IS_DEFAULT(PrefetchFieldsAhead)) {
-    FLAG_SET_DEFAULT(PrefetchFieldsAhead, 1);
-  }
 #endif
 
   if (FLAG_IS_DEFAULT(ContendedPaddingWidth) &&
@@ -1883,9 +1880,6 @@ void VM_Version::get_processor_features() {
     if (PrefetchScanIntervalInBytes > 0) {
       log->print_cr("PrefetchScanIntervalInBytes %d", (int) PrefetchScanIntervalInBytes);
     }
-    if (PrefetchFieldsAhead > 0) {
-      log->print_cr("PrefetchFieldsAhead %d", (int) PrefetchFieldsAhead);
-    }
     if (ContendedPaddingWidth > 0) {
       log->print_cr("ContendedPaddingWidth %d", (int) ContendedPaddingWidth);
     }

src/hotspot/share/gc/shared/gc_globals.hpp

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 1997, 2021, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 1997, 2022, Oracle and/or its affiliates. All rights reserved.
  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
  *
  * This code is free software; you can redistribute it and/or modify it
@@ -503,10 +503,6 @@
           "How far ahead to prefetch scan area (<= 0 means off)")           \
           range(-1, max_jint)                                               \
                                                                             \
-  product(intx, PrefetchFieldsAhead, -1,                                    \
-          "How many fields ahead to prefetch in oop scan (<= 0 means off)") \
-          range(-1, max_jint)                                               \
-                                                                            \
   product(bool, VerifyDuringStartup, false, DIAGNOSTIC,                     \
           "Verify memory system before executing any Java code "            \
           "during VM initialization")                                       \

src/hotspot/share/runtime/arguments.cpp

@@ -548,6 +548,7 @@ static SpecialFlag const special_jvm_flags[] = {
 
   { "FilterSpuriousWakeups",        JDK_Version::jdk(18), JDK_Version::jdk(19), JDK_Version::jdk(20) },
   { "MinInliningThreshold",         JDK_Version::jdk(18), JDK_Version::jdk(19), JDK_Version::jdk(20) },
+  { "PrefetchFieldsAhead",          JDK_Version::undefined(), JDK_Version::jdk(19), JDK_Version::jdk(20) },
 #ifdef ASSERT
   { "DummyObsoleteTestFlag",        JDK_Version::undefined(), JDK_Version::jdk(18), JDK_Version::undefined() },
 #endif