--- old/src/share/vm/c1/c1_CodeStubs.hpp	2011-03-28 10:10:07.117440000 -0700
+++ new/src/share/vm/c1/c1_CodeStubs.hpp	2011-03-28 10:10:06.905677000 -0700
@@ -519,36 +519,56 @@
 // Code stubs for Garbage-First barriers.
 class G1PreBarrierStub: public CodeStub {
  private:
+  bool _do_load;
   LIR_Opr _addr;
   LIR_Opr _pre_val;
   LIR_PatchCode _patch_code;
   CodeEmitInfo* _info;
 
  public:
-  // pre_val (a temporary register) must be a register;
+ 
+  // Version that _does_ generate a load of the previous value from addr.
   // addr (the address of the field to be read) must be a LIR_Address
+  // pre_val (a temporary register) must be a register;
   G1PreBarrierStub(LIR_Opr addr, LIR_Opr pre_val, LIR_PatchCode patch_code, CodeEmitInfo* info) :
-    _addr(addr), _pre_val(pre_val), _patch_code(patch_code), _info(info)
+    _addr(addr), _pre_val(pre_val), _do_load(true),
+    _patch_code(patch_code), _info(info)
   {
     assert(_pre_val->is_register(), "should be temporary register");
     assert(_addr->is_address(), "should be the address of the field");
   }
 
+  // Version that _does not_ generate load of the previous value; the
+  // previous value is assumed to have already been loaded into pre_val.
+  G1PreBarrierStub(LIR_Opr pre_val) :
+    _addr(LIR_OprFact::illegalOpr), _pre_val(pre_val), _do_load(false),
+    _patch_code(lir_patch_none), _info(NULL)
+  {
+    assert(_pre_val->is_register(), "should be a register");
+  }
+
   LIR_Opr addr() const { return _addr; }
   LIR_Opr pre_val() const { return _pre_val; }
   LIR_PatchCode patch_code() const { return _patch_code; }
   CodeEmitInfo* info() const { return _info; }
+  bool do_load() const { return _do_load; }
 
   virtual void emit_code(LIR_Assembler* e);
   virtual void visit(LIR_OpVisitState* visitor) {
-    // don't pass in the code emit info since it's processed in the fast
-    // path
-    if (_info != NULL)
-      visitor->do_slow_case(_info);
-    else
+    if (_do_load) {
+      // don't pass in the code emit info since it's processed in the fast
+      // path
+      if (_info != NULL)
+        visitor->do_slow_case(_info);
+      else
+        visitor->do_slow_case();
+
+      visitor->do_input(_addr);
+      visitor->do_temp(_pre_val);
+    } else {
       visitor->do_slow_case();
-    visitor->do_input(_addr);
-    visitor->do_temp(_pre_val);
+      visitor->do_input(_pre_val);
+    }
   }
 #ifndef PRODUCT
   virtual void print_name(outputStream* out) const { out->print("G1PreBarrierStub"); }