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

runtime/vm/stub_code_arm.cc

 // Copyright (c) 2013, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 #include "vm/globals.h"
 #if defined(TARGET_ARCH_ARM)
 
 #include "vm/assembler.h"
 #include "vm/code_generator.h"
 #include "vm/compiler.h"
@@ skipping 858 matching lines @@
 
 DECLARE_LEAF_RUNTIME_ENTRY(void, StoreBufferBlockProcess, Isolate* isolate);
 
 // Helper stub to implement Assembler::StoreIntoObject.
 // Input parameters:
 //   R0: address (i.e. object) being stored into.
 void StubCode::GenerateUpdateStoreBufferStub(Assembler* assembler) {
   // Save values being destroyed.
   __ PushList((1 << R1) | (1 << R2) | (1 << R3));
 
+  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
+  __ ldr(R2, FieldAddress(R0, Object::tags_offset()));
+  __ tst(R2, ShifterOperand(1 << RawObject::kRememberedBit));
+  __ b(&add_to_buffer, EQ);
+  __ PopList((1 << R1) | (1 << R2) | (1 << R3));
+  __ Ret();
+
+  __ Bind(&add_to_buffer);
+  __ orr(R2, R2, ShifterOperand(1 << RawObject::kRememberedBit));
+  __ str(R2, FieldAddress(R0, Object::tags_offset()));
+
   // Load the isolate out of the context.
   // Spilled: R1, R2, R3.
   // R0: address being stored.
   __ ldr(R1, FieldAddress(CTX, Context::isolate_offset()));
 
   // Load top_ out of the StoreBufferBlock and add the address to the pointers_.
   // R1: isolate.
   intptr_t store_buffer_offset = Isolate::store_buffer_block_offset();
   __ LoadFromOffset(kLoadWord, R2, R1,
                     store_buffer_offset + StoreBufferBlock::top_offset());
@@ skipping 1014 matching lines @@
   __ Bind(&reference_compare);
   __ cmp(left, ShifterOperand(right));
   __ Bind(&done);
   __ PopList((1 << R0) | (1 << R1) | (1 << R2));
   __ Ret();
 }
 
 }  // namespace dart
 
 #endif  // defined TARGET_ARCH_ARM