--- a/hotspot/src/cpu/x86/vm/templateInterpreter_x86_64.cpp	Tue Apr 05 19:14:03 2011 -0700
+++ b/hotspot/src/cpu/x86/vm/templateInterpreter_x86_64.cpp	Thu Apr 07 09:53:20 2011 -0700
@@ -757,6 +757,95 @@
   return entry_point;
 }
 
+// Method entry for java.lang.ref.Reference.get.
+address InterpreterGenerator::generate_Reference_get_entry(void) {
+#ifndef SERIALGC
+  // Code: _aload_0, _getfield, _areturn
+  // parameter size = 1
+  //
+  // The code that gets generated by this routine is split into 2 parts:
+  //    1. The "intrinsified" code for G1 (or any SATB based GC),
+  //    2. The slow path - which is an expansion of the regular method entry.
+  //
+  // Notes:-
+  // * In the G1 code we do not check whether we need to block for
+  //   a safepoint. If G1 is enabled then we must execute the specialized
+  //   code for Reference.get (except when the Reference object is null)
+  //   so that we can log the value in the referent field with an SATB
+  //   update buffer.
+  //   If the code for the getfield template is modified so that the
+  //   G1 pre-barrier code is executed when the current method is
+  //   Reference.get() then going through the normal method entry
+  //   will be fine.
+  // * The G1 code can, however, check the receiver object (the instance
+  //   of java.lang.Reference) and jump to the slow path if null. If the
+  //   Reference object is null then we obviously cannot fetch the referent
+  //   and so we don't need to call the G1 pre-barrier. Thus we can use the
+  //   regular method entry code to generate the NPE.
+  //
+  // This code is based on generate_accessor_enty.
+  //
+  // rbx: methodOop
+
+  // r13: senderSP must preserve for slow path, set SP to it on fast path
+
+  address entry = __ pc();
+
+  const int referent_offset = java_lang_ref_Reference::referent_offset;
+  guarantee(referent_offset > 0, "referent offset not initialized");
+
+  if (UseG1GC) {
+    Label slow_path;
+    // rbx: method
+
+    // Check if local 0 != NULL
+    // If the receiver is null then it is OK to jump to the slow path.
+    __ movptr(rax, Address(rsp, wordSize));
+
+    __ testptr(rax, rax);
+    __ jcc(Assembler::zero, slow_path);
+
+    // rax: local 0
+    // rbx: method (but can be used as scratch now)
+    // rdx: scratch
+    // rdi: scratch
+
+    // Generate the G1 pre-barrier code to log the value of
+    // the referent field in an SATB buffer.
+
+    // Load the value of the referent field.
+    const Address field_address(rax, referent_offset);
+    __ load_heap_oop(rax, field_address);
+
+    // Generate the G1 pre-barrier code to log the value of
+    // the referent field in an SATB buffer.
+    __ g1_write_barrier_pre(noreg /* obj */,
+                            rax /* pre_val */,
+                            r15_thread /* thread */,
+                            rbx /* tmp */,
+                            true /* tosca_live */,
+                            true /* expand_call */);
+
+    // _areturn
+    __ pop(rdi);                // get return address
+    __ mov(rsp, r13);           // set sp to sender sp
+    __ jmp(rdi);
+    __ ret(0);
+
+    // generate a vanilla interpreter entry as the slow path
+    __ bind(slow_path);
+    (void) generate_normal_entry(false);
+
+    return entry;
+  }
+#endif // SERIALGC
+
+  // If G1 is not enabled then attempt to go through the accessor entry point
+  // Reference.get is an accessor
+  return generate_accessor_entry();
+}
+
+
 // Interpreter stub for calling a native method. (asm interpreter)
 // This sets up a somewhat different looking stack for calling the
 // native method than the typical interpreter frame setup.
@@ -1463,6 +1552,8 @@
   case Interpreter::java_lang_math_log     : // fall thru
   case Interpreter::java_lang_math_log10   : // fall thru
   case Interpreter::java_lang_math_sqrt    : entry_point = ((InterpreterGenerator*) this)->generate_math_entry(kind);    break;
+  case Interpreter::java_lang_ref_reference_get
+                                           : entry_point = ((InterpreterGenerator*)this)->generate_Reference_get_entry(); break;
   default                                  : ShouldNotReachHere();                                                       break;
   }