8352565: Add native method implementation of Reference.get()

Kim Barrett · Kim Barrett · commit 56c75453cd69 · 2025-06-25T18:22:06.000Z
Reviewed-by: vlivanov, tschatzl, lmesnik
diff --git a/src/hotspot/share/c1/c1_Compiler.cpp b/src/hotspot/share/c1/c1_Compiler.cpp
@@ -141,7 +141,7 @@ bool Compiler::is_intrinsic_supported(vmIntrinsics::ID id) {
   case vmIntrinsics::_arraycopy:
   case vmIntrinsics::_currentTimeMillis:
   case vmIntrinsics::_nanoTime:
-  case vmIntrinsics::_Reference_get:
+  case vmIntrinsics::_Reference_get0:
     // Use the intrinsic version of Reference.get() so that the value in
     // the referent field can be registered by the G1 pre-barrier code.
     // Also to prevent commoning reads from this field across safepoint
diff --git a/src/hotspot/share/c1/c1_GraphBuilder.cpp b/src/hotspot/share/c1/c1_GraphBuilder.cpp
@@ -3340,7 +3340,7 @@ GraphBuilder::GraphBuilder(Compilation* compilation, IRScope* scope)
       break;
     }
 
-  case vmIntrinsics::_Reference_get:
+  case vmIntrinsics::_Reference_get0:
     {
       {
         // With java.lang.ref.reference.get() we must go through the
diff --git a/src/hotspot/share/c1/c1_LIRGenerator.cpp b/src/hotspot/share/c1/c1_LIRGenerator.cpp
@@ -1185,7 +1185,7 @@ void LIRGenerator::do_Return(Return* x) {
 
 // Example: ref.get()
 // Combination of LoadField and g1 pre-write barrier
-void LIRGenerator::do_Reference_get(Intrinsic* x) {
+void LIRGenerator::do_Reference_get0(Intrinsic* x) {
 
   const int referent_offset = java_lang_ref_Reference::referent_offset();
 
@@ -2914,8 +2914,8 @@ void LIRGenerator::do_Intrinsic(Intrinsic* x) {
   case vmIntrinsics::_onSpinWait:
     __ on_spin_wait();
     break;
-  case vmIntrinsics::_Reference_get:
-    do_Reference_get(x);
+  case vmIntrinsics::_Reference_get0:
+    do_Reference_get0(x);
     break;
 
   case vmIntrinsics::_updateCRC32:
diff --git a/src/hotspot/share/c1/c1_LIRGenerator.hpp b/src/hotspot/share/c1/c1_LIRGenerator.hpp
@@ -266,7 +266,7 @@ class LIRGenerator: public InstructionVisitor, public BlockClosure {
   void do_CompareAndSwap(Intrinsic* x, ValueType* type);
   void do_PreconditionsCheckIndex(Intrinsic* x, BasicType type);
   void do_FPIntrinsics(Intrinsic* x);
-  void do_Reference_get(Intrinsic* x);
+  void do_Reference_get0(Intrinsic* x);
   void do_update_CRC32(Intrinsic* x);
   void do_update_CRC32C(Intrinsic* x);
   void do_vectorizedMismatch(Intrinsic* x);
diff --git a/src/hotspot/share/classfile/vmIntrinsics.cpp b/src/hotspot/share/classfile/vmIntrinsics.cpp
@@ -99,7 +99,7 @@ bool vmIntrinsics::preserves_state(vmIntrinsics::ID id) {
   case vmIntrinsics::_dpow:
   case vmIntrinsics::_Preconditions_checkIndex:
   case vmIntrinsics::_Preconditions_checkLongIndex:
-  case vmIntrinsics::_Reference_get:
+  case vmIntrinsics::_Reference_get0:
   case vmIntrinsics::_Continuation_doYield:
   case vmIntrinsics::_updateCRC32:
   case vmIntrinsics::_updateBytesCRC32:
@@ -244,7 +244,7 @@ bool vmIntrinsics::disabled_by_jvm_flags(vmIntrinsics::ID id) {
     case vmIntrinsics::_storeFence:
     case vmIntrinsics::_fullFence:
     case vmIntrinsics::_countPositives:
-    case vmIntrinsics::_Reference_get:
+    case vmIntrinsics::_Reference_get0:
     case vmIntrinsics::_Continuation_doYield:
     case vmIntrinsics::_Continuation_enterSpecial:
     case vmIntrinsics::_Continuation_pin:
diff --git a/src/hotspot/share/classfile/vmIntrinsics.hpp b/src/hotspot/share/classfile/vmIntrinsics.hpp
@@ -461,7 +461,7 @@ class methodHandle;
    do_signature(vectorizedMismatch_signature, "(Ljava/lang/Object;JLjava/lang/Object;JII)I")                            \
                                                                                                                         \
   /* java/lang/ref/Reference */                                                                                         \
-  do_intrinsic(_Reference_get,              java_lang_ref_Reference, get_name,       void_object_signature,    F_R)     \
+  do_intrinsic(_Reference_get0,             java_lang_ref_Reference, get0_name,      void_object_signature,    F_RN)    \
   do_intrinsic(_Reference_refersTo0,        java_lang_ref_Reference, refersTo0_name, object_boolean_signature, F_RN)    \
   do_intrinsic(_PhantomReference_refersTo0, java_lang_ref_PhantomReference, refersTo0_name, object_boolean_signature, F_RN) \
   do_intrinsic(_Reference_clear0,           java_lang_ref_Reference, clear0_name,    void_method_signature, F_RN)       \
diff --git a/src/hotspot/share/classfile/vmSymbols.hpp b/src/hotspot/share/classfile/vmSymbols.hpp
@@ -422,7 +422,7 @@ class SerializeClosure;
   template(sp_name,                                   "sp")                                       \
   template(pc_name,                                   "pc")                                       \
   template(cs_name,                                   "cs")                                       \
-  template(get_name,                                  "get")                                      \
+  template(get0_name,                                 "get0")                                     \
   template(refersTo0_name,                            "refersTo0")                                \
   template(clear0_name,                               "clear0")                                   \
   template(put_name,                                  "put")                                      \
diff --git a/src/hotspot/share/include/jvm.h b/src/hotspot/share/include/jvm.h
@@ -353,6 +353,9 @@ JVM_HasReferencePendingList(JNIEnv *env);
 JNIEXPORT void JNICALL
 JVM_WaitForReferencePendingList(JNIEnv *env);
 
+JNIEXPORT jobject JNICALL
+JVM_ReferenceGet(JNIEnv *env, jobject ref);
+
 JNIEXPORT jboolean JNICALL
 JVM_ReferenceRefersTo(JNIEnv *env, jobject ref, jobject o);
 
diff --git a/src/hotspot/share/interpreter/abstractInterpreter.cpp b/src/hotspot/share/interpreter/abstractInterpreter.cpp
@@ -148,7 +148,7 @@ AbstractInterpreter::MethodKind AbstractInterpreter::method_kind(const methodHan
       case vmIntrinsics::_fmaF:              return java_lang_math_fmaF;
       case vmIntrinsics::_dsqrt:             return java_lang_math_sqrt;
       case vmIntrinsics::_dsqrt_strict:      return java_lang_math_sqrt_strict;
-      case vmIntrinsics::_Reference_get:     return java_lang_ref_reference_get;
+      case vmIntrinsics::_Reference_get0:    return java_lang_ref_reference_get0;
       case vmIntrinsics::_Object_init:
         if (m->code_size() == 1) {
           // We need to execute the special return bytecode to check for
@@ -210,7 +210,7 @@ vmIntrinsics::ID AbstractInterpreter::method_intrinsic(MethodKind kind) {
   case java_lang_math_exp         : return vmIntrinsics::_dexp;
   case java_lang_math_fmaD        : return vmIntrinsics::_fmaD;
   case java_lang_math_fmaF        : return vmIntrinsics::_fmaF;
-  case java_lang_ref_reference_get: return vmIntrinsics::_Reference_get;
+  case java_lang_ref_reference_get0: return vmIntrinsics::_Reference_get0;
   case java_util_zip_CRC32_update : return vmIntrinsics::_updateCRC32;
   case java_util_zip_CRC32_updateBytes
                                   : return vmIntrinsics::_updateBytesCRC32;
@@ -320,7 +320,7 @@ void AbstractInterpreter::print_method_kind(MethodKind kind) {
     case java_util_zip_CRC32_updateByteBuffer : tty->print("java_util_zip_CRC32_updateByteBuffer"); break;
     case java_util_zip_CRC32C_updateBytes     : tty->print("java_util_zip_CRC32C_updateBytes"); break;
     case java_util_zip_CRC32C_updateDirectByteBuffer: tty->print("java_util_zip_CRC32C_updateDirectByteByffer"); break;
-    case java_lang_ref_reference_get          : tty->print("java_lang_ref_reference_get"); break;
+    case java_lang_ref_reference_get0         : tty->print("java_lang_ref_reference_get0"); break;
     case java_lang_Thread_currentThread       : tty->print("java_lang_Thread_currentThread"); break;
     case java_lang_Float_float16ToFloat       : tty->print("java_lang_Float_float16ToFloat"); break;
     case java_lang_Float_floatToFloat16       : tty->print("java_lang_Float_floatToFloat16"); break;
diff --git a/src/hotspot/share/interpreter/abstractInterpreter.hpp b/src/hotspot/share/interpreter/abstractInterpreter.hpp
@@ -83,7 +83,7 @@ class AbstractInterpreter: AllStatic {
     java_lang_math_exp,                                         // implementation of java.lang.Math.exp   (x)
     java_lang_math_fmaF,                                        // implementation of java.lang.Math.fma   (x, y, z)
     java_lang_math_fmaD,                                        // implementation of java.lang.Math.fma   (x, y, z)
-    java_lang_ref_reference_get,                                // implementation of java.lang.ref.Reference.get()
+    java_lang_ref_reference_get0,                               // implementation of java.lang.ref.Reference.get()
     java_util_zip_CRC32_update,                                 // implementation of java.util.zip.CRC32.update()
     java_util_zip_CRC32_updateBytes,                            // implementation of java.util.zip.CRC32.updateBytes()
     java_util_zip_CRC32_updateByteBuffer,                       // implementation of java.util.zip.CRC32.updateByteBuffer()
diff --git a/src/hotspot/share/interpreter/templateInterpreterGenerator.cpp b/src/hotspot/share/interpreter/templateInterpreterGenerator.cpp
@@ -204,7 +204,7 @@ void TemplateInterpreterGenerator::generate_all() {
   method_entry(java_lang_math_pow  )
   method_entry(java_lang_math_fmaF )
   method_entry(java_lang_math_fmaD )
-  method_entry(java_lang_ref_reference_get)
+  method_entry(java_lang_ref_reference_get0)
   AbstractInterpreter::initialize_method_handle_entries();
 
   method_entry(java_util_zip_CRC32C_updateBytes)
@@ -228,6 +228,7 @@ void TemplateInterpreterGenerator::generate_all() {
   // entries for `native` methods to use the same address in case
   // intrinsic is disabled.
   native_method_entry(java_lang_Thread_currentThread)
+  native_method_entry(java_lang_ref_reference_get0)
 
   native_method_entry(java_util_zip_CRC32_update)
   native_method_entry(java_util_zip_CRC32_updateBytes)
@@ -465,7 +466,7 @@ address TemplateInterpreterGenerator::generate_intrinsic_entry(AbstractInterpret
   case Interpreter::java_lang_math_fmaF    : entry_point = generate_math_entry(kind);      break;
   case Interpreter::java_lang_math_sqrt_strict
                                            : entry_point = generate_math_entry(Interpreter::java_lang_math_sqrt); break;
-  case Interpreter::java_lang_ref_reference_get
+  case Interpreter::java_lang_ref_reference_get0
                                            : entry_point = generate_Reference_get_entry(); break;
   case Interpreter::java_util_zip_CRC32_update
                                            : entry_point = generate_CRC32_update_entry();  break;
diff --git a/src/hotspot/share/interpreter/zero/zeroInterpreterGenerator.cpp b/src/hotspot/share/interpreter/zero/zeroInterpreterGenerator.cpp
@@ -64,7 +64,7 @@ void ZeroInterpreterGenerator::generate_all() {
     method_entry(java_lang_math_exp );
     method_entry(java_lang_math_fmaD );
     method_entry(java_lang_math_fmaF );
-    method_entry(java_lang_ref_reference_get);
+    method_entry(java_lang_ref_reference_get0);
 
     AbstractInterpreter::initialize_method_handle_entries();
 
@@ -107,7 +107,7 @@ address ZeroInterpreterGenerator::generate_method_entry(
   case Interpreter::java_lang_math_exp     : // fall thru
   case Interpreter::java_lang_math_fmaD    : // fall thru
   case Interpreter::java_lang_math_fmaF    : entry_point = generate_math_entry(kind);      break;
-  case Interpreter::java_lang_ref_reference_get
+  case Interpreter::java_lang_ref_reference_get0
                                            : entry_point = generate_Reference_get_entry(); break;
   default:
     fatal("unexpected method kind: %d", kind);
diff --git a/src/hotspot/share/opto/c2compiler.cpp b/src/hotspot/share/opto/c2compiler.cpp
@@ -767,7 +767,7 @@ bool C2Compiler::is_intrinsic_supported(vmIntrinsics::ID id) {
   case vmIntrinsics::_doubleToRawLongBits:
   case vmIntrinsics::_doubleToLongBits:
   case vmIntrinsics::_longBitsToDouble:
-  case vmIntrinsics::_Reference_get:
+  case vmIntrinsics::_Reference_get0:
   case vmIntrinsics::_Reference_refersTo0:
   case vmIntrinsics::_PhantomReference_refersTo0:
   case vmIntrinsics::_Reference_clear0:
diff --git a/src/hotspot/share/opto/compile.cpp b/src/hotspot/share/opto/compile.cpp
@@ -783,19 +783,9 @@ Compile::Compile(ciEnv* ci_env, ciMethod* target, int osr_bci,
       StartNode* s = new StartNode(root(), tf()->domain());
       initial_gvn()->set_type_bottom(s);
       verify_start(s);
-      if (method()->intrinsic_id() == vmIntrinsics::_Reference_get) {
-        // With java.lang.ref.reference.get() we must go through the
-        // intrinsic - even when get() is the root
-        // method of the compile - so that, if necessary, the value in
-        // the referent field of the reference object gets recorded by
-        // the pre-barrier code.
-        cg = find_intrinsic(method(), false);
-      }
-      if (cg == nullptr) {
-        float past_uses = method()->interpreter_invocation_count();
-        float expected_uses = past_uses;
-        cg = CallGenerator::for_inline(method(), expected_uses);
-      }
+      float past_uses = method()->interpreter_invocation_count();
+      float expected_uses = past_uses;
+      cg = CallGenerator::for_inline(method(), expected_uses);
     }
     if (failing())  return;
     if (cg == nullptr) {
diff --git a/src/hotspot/share/opto/library_call.cpp b/src/hotspot/share/opto/library_call.cpp
@@ -564,7 +564,7 @@ bool LibraryCallKit::try_to_inline(int predicate) {
 
   case vmIntrinsics::_getCallerClass:           return inline_native_Reflection_getCallerClass();
 
-  case vmIntrinsics::_Reference_get:            return inline_reference_get();
+  case vmIntrinsics::_Reference_get0:           return inline_reference_get0();
   case vmIntrinsics::_Reference_refersTo0:      return inline_reference_refersTo0(false);
   case vmIntrinsics::_PhantomReference_refersTo0: return inline_reference_refersTo0(true);
   case vmIntrinsics::_Reference_clear0:         return inline_reference_clear0(false);
@@ -6923,9 +6923,9 @@ bool LibraryCallKit::inline_updateByteBufferAdler32() {
   return true;
 }
 
-//----------------------------inline_reference_get----------------------------
+//----------------------------inline_reference_get0----------------------------
 // public T java.lang.ref.Reference.get();
-bool LibraryCallKit::inline_reference_get() {
+bool LibraryCallKit::inline_reference_get0() {
   const int referent_offset = java_lang_ref_Reference::referent_offset();
 
   // Get the argument:
diff --git a/src/hotspot/share/opto/library_call.hpp b/src/hotspot/share/opto/library_call.hpp
@@ -300,7 +300,7 @@ class LibraryCallKit : public GraphKit {
   bool inline_bitshuffle_methods(vmIntrinsics::ID id);
   bool inline_compare_unsigned(vmIntrinsics::ID id);
   bool inline_divmod_methods(vmIntrinsics::ID id);
-  bool inline_reference_get();
+  bool inline_reference_get0();
   bool inline_reference_refersTo0(bool is_phantom);
   bool inline_reference_clear0(bool is_phantom);
   bool inline_Class_cast();
diff --git a/src/hotspot/share/prims/jvm.cpp b/src/hotspot/share/prims/jvm.cpp
@@ -3040,9 +3040,17 @@ JVM_ENTRY(void, JVM_WaitForReferencePendingList(JNIEnv* env))
   }
 JVM_END
 
+JVM_ENTRY(jobject, JVM_ReferenceGet(JNIEnv* env, jobject ref))
+  oop ref_oop = JNIHandles::resolve_non_null(ref);
+  // PhantomReference has its own implementation of get().
+  assert(!java_lang_ref_Reference::is_phantom(ref_oop), "precondition");
+  oop referent = java_lang_ref_Reference::weak_referent(ref_oop);
+  return JNIHandles::make_local(THREAD, referent);
+JVM_END
+
 JVM_ENTRY(jboolean, JVM_ReferenceRefersTo(JNIEnv* env, jobject ref, jobject o))
   oop ref_oop = JNIHandles::resolve_non_null(ref);
-  // PhantomReference has it's own implementation of refersTo().
+  // PhantomReference has its own implementation of refersTo().
   // See: JVM_PhantomReferenceRefersTo
   assert(!java_lang_ref_Reference::is_phantom(ref_oop), "precondition");
   oop referent = java_lang_ref_Reference::weak_referent_no_keepalive(ref_oop);
diff --git a/src/java.base/share/classes/java/lang/ref/Reference.java b/src/java.base/share/classes/java/lang/ref/Reference.java
@@ -357,11 +357,18 @@ public void runFinalization() {
      *           {@code null} if this reference object has been cleared
      * @see #refersTo
      */
-    @IntrinsicCandidate
     public T get() {
-        return this.referent;
+        return get0();
     }
 
+    /* Implementation of get().  This method exists to avoid making get() all
+     * of virtual, native, and intrinsic candidate. That could have the
+     * undesirable effect of having the native method used instead of the
+     * intrinsic when devirtualization fails.
+     */
+    @IntrinsicCandidate
+    private native T get0();
+
     /**
      * Tests if the referent of this reference object is {@code obj}.
      * Using a {@code null} {@code obj} returns {@code true} if the
diff --git a/src/java.base/share/native/libjava/Reference.c b/src/java.base/share/native/libjava/Reference.c
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2016, 2020, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2016, 2025, 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
@@ -44,6 +44,12 @@ Java_java_lang_ref_Reference_waitForReferencePendingList(JNIEnv *env, jclass ign
     JVM_WaitForReferencePendingList(env);
 }
 
+JNIEXPORT jobject JNICALL
+Java_java_lang_ref_Reference_get0(JNIEnv *env, jobject ref)
+{
+    return JVM_ReferenceGet(env, ref);
+}
+
 JNIEXPORT jboolean JNICALL
 Java_java_lang_ref_Reference_refersTo0(JNIEnv *env, jobject ref, jobject o)
 {
diff --git a/test/hotspot/jtreg/gc/TestNativeReferenceGet.java b/test/hotspot/jtreg/gc/TestNativeReferenceGet.java

Original file line number	Diff line number	Diff line change
`@@ -3340,7 +3340,7 @@ GraphBuilder::GraphBuilder(Compilation* compilation, IRScope* scope)`
`3340`	`3340`	`break;`
`3341`	`3341`	`}`
`3342`	`3342`
`3343`		`- case vmIntrinsics::_Reference_get:`
	`3343`	`+ case vmIntrinsics::_Reference_get0:`
`3344`	`3344`	`{`
`3345`	`3345`	`{`
`3346`	`3346`	`// With java.lang.ref.reference.get() we must go through the`
Original file line number	Diff line number	Diff line change
`@@ -461,7 +461,7 @@ class methodHandle;`
`461`	`461`	`do_signature(vectorizedMismatch_signature, "(Ljava/lang/Object;JLjava/lang/Object;JII)I") \`
`462`	`462`	`\`
`463`	`463`	`/* java/lang/ref/Reference */ \`
`464`		`- do_intrinsic(_Reference_get, java_lang_ref_Reference, get_name, void_object_signature, F_R) \`
	`464`	`+ do_intrinsic(_Reference_get0, java_lang_ref_Reference, get0_name, void_object_signature, F_RN) \`
`465`	`465`	`do_intrinsic(_Reference_refersTo0, java_lang_ref_Reference, refersTo0_name, object_boolean_signature, F_RN) \`
`466`	`466`	`do_intrinsic(_PhantomReference_refersTo0, java_lang_ref_PhantomReference, refersTo0_name, object_boolean_signature, F_RN) \`
`467`	`467`	`do_intrinsic(_Reference_clear0, java_lang_ref_Reference, clear0_name, void_method_signature, F_RN) \`