diff -r 570062d730b2 -r 4c24294029a9 hotspot/src/cpu/x86/vm/stubGenerator_x86_64.cpp
--- a/hotspot/src/cpu/x86/vm/stubGenerator_x86_64.cpp	Wed Jun 04 13:51:09 2008 -0700
+++ b/hotspot/src/cpu/x86/vm/stubGenerator_x86_64.cpp	Thu Jun 05 15:57:56 2008 -0700
@@ -1152,18 +1152,26 @@
   //     Destroy no registers!
   //
   void  gen_write_ref_array_pre_barrier(Register addr, Register count) {
-#if 0 // G1 - only
-    assert_different_registers(addr, c_rarg1);
-    assert_different_registers(count, c_rarg0);
     BarrierSet* bs = Universe::heap()->barrier_set();
     switch (bs->kind()) {
       case BarrierSet::G1SATBCT:
       case BarrierSet::G1SATBCTLogging:
         {
           __ pushaq();                      // push registers
-          __ movq(c_rarg0, addr);
-          __ movq(c_rarg1, count);
-          __ call(RuntimeAddress(BarrierSet::static_write_ref_array_pre));
+          if (count == c_rarg0) {
+            if (addr == c_rarg1) {
+              // exactly backwards!!
+              __ xchgq(c_rarg1, c_rarg0);
+            } else {
+              __ movq(c_rarg1, count);
+              __ movq(c_rarg0, addr);
+            }
+
+          } else {
+            __ movq(c_rarg0, addr);
+            __ movq(c_rarg1, count);
+          }
+          __ call(RuntimeAddress(CAST_FROM_FN_PTR(address, BarrierSet::static_write_ref_array_pre)));
           __ popaq();
         }
         break;
@@ -1171,11 +1179,10 @@
       case BarrierSet::CardTableExtension:
       case BarrierSet::ModRef:
         break;
-      default      :
+      default:
         ShouldNotReachHere();
 
     }
-#endif // 0 G1 - only
   }
 
   //
@@ -1192,7 +1199,6 @@
     assert_different_registers(start, end, scratch);
     BarrierSet* bs = Universe::heap()->barrier_set();
     switch (bs->kind()) {
-#if 0 // G1 - only
       case BarrierSet::G1SATBCT:
       case BarrierSet::G1SATBCTLogging:
 
@@ -1205,11 +1211,10 @@
           __ shrq(scratch, LogBytesPerWord);
           __ movq(c_rarg0, start);
           __ movq(c_rarg1, scratch);
-          __ call(RuntimeAddress(CAST_FROM_FN_PTR(address, BarrierSet::static_write_ref_array_post));
+          __ call(RuntimeAddress(CAST_FROM_FN_PTR(address, BarrierSet::static_write_ref_array_post)));
           __ popaq();
         }
         break;
-#endif // 0 G1 - only
       case BarrierSet::CardTableModRef:
       case BarrierSet::CardTableExtension:
         {
@@ -1230,8 +1235,12 @@
           __ decrementq(count);
           __ jcc(Assembler::greaterEqual, L_loop);
         }
-      }
-   }
+        break;
+      default:
+        ShouldNotReachHere();
+
+    }
+  }
 
   // Copy big chunks forward
   //