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

runtime/vm/stub_code_ia32.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_IA32)
 
 #include "vm/assembler.h"
 #include "vm/compiler.h"
 #include "vm/dart_entry.h"
@@ skipping 941 matching lines @@
 DECLARE_LEAF_RUNTIME_ENTRY(void, StoreBufferBlockProcess, Isolate* isolate);
 
 // Helper stub to implement Assembler::StoreIntoObject.
 // Input parameters:
 //   EAX: Address being stored
 void StubCode::GenerateUpdateStoreBufferStub(Assembler* assembler) {
   // Save values being destroyed.
   __ pushl(EDX);
   __ pushl(ECX);
 
+  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
+  __ movl(ECX, FieldAddress(EAX, Object::tags_offset()));

[Vyacheslav Egorov (Google), 2013/04/27 19:34:46]

I wonder if doing testl with memory operand before pushing EDX/ECX would save us
something noticeable. (it would save pushing and poping definitely)

[Ivan Posva, 2013/05/03 21:01:37]

Different CL.

+  __ testl(ECX, Immediate(1 << RawObject::kRememberedBit));
+  __ j(EQUAL, &add_to_buffer, Assembler::kNearJump);
+  __ popl(ECX);
+  __ popl(EDX);
+  __ ret();
+
+  __ Bind(&add_to_buffer);
+  __ orl(ECX, Immediate(1 << RawObject::kRememberedBit));
+  __ movl(FieldAddress(EAX, Object::tags_offset()), ECX);
+
   // Load the isolate out of the context.
   // Spilled: EDX, ECX
   // EAX: Address being stored
   __ movl(EDX, FieldAddress(CTX, Context::isolate_offset()));
 
   // Load top_ out of the StoreBufferBlock and add the address to the pointers_.
   // Spilled: EDX, ECX
   // EAX: Address being stored
   // EDX: Isolate
   intptr_t store_buffer_offset = Isolate::store_buffer_block_offset();
@@ skipping 1128 matching lines @@
   __ Bind(&done);
   __ popl(temp);
   __ popl(right);
   __ popl(left);
   __ ret();
 }
 
 }  // namespace dart
 
 #endif  // defined TARGET_ARCH_IA32