diff -r 1f809e010142 -r cf1821c649d9 src/cpu/x86/vm/assembler_x86_64.cpp
--- a/src/cpu/x86/vm/assembler_x86_64.cpp	Fri Jun 06 13:43:36 2008 -0400
+++ b/src/cpu/x86/vm/assembler_x86_64.cpp	Fri Jun 06 14:34:24 2008 -0700
@@ -5007,8 +5007,7 @@
   jcc(Assembler::notEqual, cas_label);
   // The bias pattern is present in the object's header. Need to check
   // whether the bias owner and the epoch are both still current.
-  load_klass(tmp_reg, obj_reg);
-  movq(tmp_reg, Address(tmp_reg, Klass::prototype_header_offset_in_bytes() + klassOopDesc::klass_part_offset_in_bytes()));
+  load_prototype_header(tmp_reg, obj_reg);
   orq(tmp_reg, r15_thread);
   xorq(tmp_reg, swap_reg);
   andq(tmp_reg, ~((int) markOopDesc::age_mask_in_place));
@@ -5082,8 +5081,7 @@
   //
   // FIXME: due to a lack of registers we currently blow away the age
   // bits in this situation. Should attempt to preserve them.
-  load_klass(tmp_reg, obj_reg);
-  movq(tmp_reg, Address(tmp_reg, Klass::prototype_header_offset_in_bytes() + klassOopDesc::klass_part_offset_in_bytes()));
+  load_prototype_header(tmp_reg, obj_reg);
   orq(tmp_reg, r15_thread);
   if (os::is_MP()) {
     lock();
@@ -5113,8 +5111,7 @@
   //
   // FIXME: due to a lack of registers we currently blow away the age
   // bits in this situation. Should attempt to preserve them.
-  load_klass(tmp_reg, obj_reg);
-  movq(tmp_reg, Address(tmp_reg, Klass::prototype_header_offset_in_bytes() + klassOopDesc::klass_part_offset_in_bytes()));
+  load_prototype_header(tmp_reg, obj_reg);
   if (os::is_MP()) {
     lock();
   }
@@ -5158,6 +5155,16 @@
   }
 }
 
+void MacroAssembler::load_prototype_header(Register dst, Register src) {
+  if (UseCompressedOops) {
+    movl(dst, Address(src, oopDesc::klass_offset_in_bytes()));
+    movq(dst, Address(r12_heapbase, dst, Address::times_8, Klass::prototype_header_offset_in_bytes() + klassOopDesc::klass_part_offset_in_bytes()));
+  } else {
+    movq(dst, Address(src, oopDesc::klass_offset_in_bytes()));
+    movq(dst, Address(dst, Klass::prototype_header_offset_in_bytes() + klassOopDesc::klass_part_offset_in_bytes()));
+  }
+}
+
 void MacroAssembler::store_klass(Register dst, Register src) {
   if (UseCompressedOops) {
     encode_heap_oop_not_null(src);