- Remember the fact that an object has been added to the

runtime/vm/stub_code_x64.cc

Index: runtime/vm/stub_code_x64.cc
===================================================================
--- runtime/vm/stub_code_x64.cc	(revision 22083)
+++ runtime/vm/stub_code_x64.cc	(working copy)
@@ -948,6 +948,22 @@
   __ pushq(RDX);
   __ pushq(RCX);
 
+  Label add_to_buffer;
+  // Check whether this object has already been remembered. Skip adding to the
+  // store buffer if the object is in the store buffer already.
+  // Spilled: EDX, ECX
+  // EAX: Address being stored
+  __ movq(RCX, FieldAddress(RAX, Object::tags_offset()));
+  __ testq(RCX, Immediate(1 << RawObject::kRememberedBit));
+  __ j(EQUAL, &add_to_buffer, Assembler::kNearJump);
+  __ popq(RCX);
+  __ popq(RDX);
+  __ ret();
+
+  __ Bind(&add_to_buffer);
+  __ orq(RCX, Immediate(1 << RawObject::kRememberedBit));
+  __ movq(FieldAddress(RAX, Object::tags_offset()), RCX);
+
   // Load the isolate out of the context.
   // RAX: Address being stored
   __ movq(RDX, FieldAddress(CTX, Context::isolate_offset()));