Put back the asserts in RememberedSetHelper, but correct this time.

src/x64/macro-assembler-x64.cc

 // Copyright 2011 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 179 matching lines @@
 
 void MacroAssembler::CompareRoot(const Operand& with,
                                  Heap::RootListIndex index) {
   ASSERT(root_array_available_);
   ASSERT(!with.AddressUsesRegister(kScratchRegister));
   LoadRoot(kScratchRegister, index);
   cmpq(with, kScratchRegister);
 }
 
 
-void MacroAssembler::RememberedSetHelper(Register addr,
+void MacroAssembler::RememberedSetHelper(Register object,  // For debug tests.
+                                         Register addr,
                                          Register scratch,
                                          SaveFPRegsMode save_fp,
                                          RememberedSetFinalAction and_then) {
+  if (FLAG_debug_code) {
+    Label ok;
+    JumpIfNotInNewSpace(object, scratch, &ok, Label::kNear);
+    int3();
+    bind(&ok);
+  }
   // Load store buffer top.
   LoadRoot(scratch, Heap::kStoreBufferTopRootIndex);
   // Store pointer to buffer.
   movq(Operand(scratch, 0), addr);
   // Increment buffer top.
   addq(scratch, Immediate(kPointerSize));
   // Write back new top of buffer.
   StoreRoot(scratch, Heap::kStoreBufferTopRootIndex);
   // Call stub on end of buffer.
   Label done;
@@ skipping 3975 matching lines @@
 
   and_(bitmap_scratch, Immediate(~Page::kPageAlignmentMask));
   addl(Operand(bitmap_scratch, MemoryChunk::kLiveBytesOffset), length);
 
   bind(&done);
 }
 
 } }  // namespace v8::internal
 
 #endif  // V8_TARGET_ARCH_X64