8307532: Implement LM_LIGHTWEIGHT for Zero

Reviewed-by: aboldtch, jwaters

Author: rkennke

src/hotspot/cpu/zero/vm_version_zero.cpp

@@ -116,11 +116,6 @@ void VM_Version::initialize() {
     FLAG_SET_DEFAULT(UseVectorizedMismatchIntrinsic, false);
   }
 
-  if ((LockingMode != LM_LEGACY) && (LockingMode != LM_MONITOR)) {
-    warning("Unsupported locking mode for this CPU.");
-    FLAG_SET_DEFAULT(LockingMode, LM_LEGACY);
-  }
-
   // Enable error context decoding on known platforms
 #if defined(IA32) || defined(AMD64) || defined(ARM) || \
     defined(AARCH64) || defined(PPC) || defined(RISCV) || \

src/hotspot/cpu/zero/zeroInterpreter_zero.cpp

@@ -485,26 +485,30 @@ int ZeroInterpreter::native_entry(Method* method, intptr_t UNUSED, TRAPS) {
 
   // Unlock if necessary
   if (monitor) {
-    BasicLock *lock = monitor->lock();
-    markWord header = lock->displaced_header();
-    oop rcvr = monitor->obj();
-    monitor->set_obj(nullptr);
-
-    bool dec_monitor_count = true;
-    if (header.to_pointer() != nullptr) {
-      markWord old_header = markWord::encode(lock);
-      if (rcvr->cas_set_mark(header, old_header) != old_header) {
-        monitor->set_obj(rcvr);
-        dec_monitor_count = false;
-        InterpreterRuntime::monitorexit(monitor);
+    bool success = false;
+    if (LockingMode == LM_LEGACY) {
+      BasicLock* lock = monitor->lock();
+      oop rcvr = monitor->obj();
+      monitor->set_obj(nullptr);
+      success = true;
+      markWord header = lock->displaced_header();
+      if (header.to_pointer() != nullptr) { // Check for recursive lock
+        markWord old_header = markWord::encode(lock);
+        if (rcvr->cas_set_mark(header, old_header) != old_header) {
+          monitor->set_obj(rcvr);
+          success = false;
+        }
+      }
+      if (success) {
+        THREAD->dec_held_monitor_count();
       }
     }
-    if (dec_monitor_count) {
-      THREAD->dec_held_monitor_count();
+    if (!success) {
+      InterpreterRuntime::monitorexit(monitor);
     }
   }
 
- unwind_and_return:
+  unwind_and_return:
 
   // Unwind the current activation
   thread->pop_zero_frame();

src/hotspot/share/runtime/arguments.cpp

@@ -1817,17 +1817,6 @@ bool Arguments::check_vm_args_consistency() {
   }
 #endif
 
-#if !defined(X86) && !defined(AARCH64) && !defined(RISCV64) && !defined(ARM) && !defined(PPC64) && !defined(S390)
-  if (LockingMode == LM_LIGHTWEIGHT) {
-    FLAG_SET_CMDLINE(LockingMode, LM_LEGACY);
-    warning("New lightweight locking not supported on this platform");
-  }
-  if (UseObjectMonitorTable) {
-    FLAG_SET_CMDLINE(UseObjectMonitorTable, false);
-    warning("UseObjectMonitorTable not supported on this platform");
-  }
-#endif
-
   if (UseObjectMonitorTable && LockingMode != LM_LIGHTWEIGHT) {
     // ObjectMonitorTable requires lightweight locking.
     FLAG_SET_CMDLINE(UseObjectMonitorTable, false);

src/hotspot/share/runtime/basicLock.inline.hpp

@@ -39,7 +39,7 @@ inline void BasicLock::set_displaced_header(markWord header) {
 
 inline ObjectMonitor* BasicLock::object_monitor_cache() const {
   assert(UseObjectMonitorTable, "must be");
-#if defined(X86) || defined(AARCH64) || defined(RISCV64) || defined(PPC64) || defined(S390)
+#if !defined(ZERO) && (defined(X86) || defined(AARCH64) || defined(RISCV64) || defined(PPC64) || defined(S390))
   return reinterpret_cast<ObjectMonitor*>(get_metadata());
 #else
   // Other platforms do not make use of the cache yet,