Generate code for store buffer updates in open-coded object field stores.

runtime/vm/assembler_ia32.cc

 // Copyright (c) 2011, 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/heap.h"
 #include "vm/memory_region.h"
 #include "vm/runtime_entry.h"
 #include "vm/stub_code.h"
 
 namespace dart {
 
+DECLARE_RUNTIME_ENTRY(StoreBuffer);
+
 DEFINE_FLAG(bool, print_stop_message, true, "Print stop message.");
 DEFINE_FLAG(bool, code_comments, false,
             "Include comments into code and disassembly");
 
 
 class DirectCallRelocation : public AssemblerFixup {
  public:
   void Process(const MemoryRegion& region, int position) {
     // Direct calls are relative to the following instruction on x86.
     int32_t pointer = region.Load<int32_t>(position);
@@ skipping 1331 matching lines @@
       EmitOperand(7, Operand(reg));
       buffer_.EmitObject(object);
     }
   }
 }
 
 
 void Assembler::StoreIntoObject(Register object,
                                 const FieldAddress& dest,
                                 Register value) {
-  // TODO(iposva): Add write barrier.
   movl(dest, value);
+  Label done;
+  // Check that 'value' is a new object.  Store buffer updates are not
+  // required when storing a smi or an old object.
+  testl(value, Immediate(kNewObjectAlignmentOffset | kHeapObjectTag));
+  j(NOT_EQUAL, &done, Assembler::kNearJump);
+  // Check that 'object' is an old object.  A store buffer update is
+  // not required when storing into a new object.
+  testl(object, Immediate(kOldObjectAlignmentOffset | kHeapObjectTag));
+  j(NOT_EQUAL, &done, Assembler::kNearJump);
+  // A store buffer update is required.
+  pushl(object);  // Save 'object' register
+  pushl(value);  // Save 'value' register
+  pushl(dest);  // Push argument

[cshapiro, 2012/06/12 21:41:01]

Apparently, this store is not legal since it is an interior pointer and not an
object pointer.

+  CallRuntime(kStoreBufferRuntimeEntry);
+  popl(value);  // Pop argument
+  popl(value);  // Restore 'value' register
+  popl(object);  // Restore 'object' register
+  Bind(&done);
 }
 
 
+void Assembler::StoreIntoObjectNoBarrier(Register object,
+                                         const FieldAddress& dest,
+                                         Register value) {
+  movl(dest, value);
+  // No store buffer update.
+#if defined(DEBUG)
+  Label done;
+  testl(value, Immediate(kNewObjectAlignmentOffset | kHeapObjectTag));
+  j(NOT_EQUAL, &done, Assembler::kNearJump);
+  testl(object, Immediate(kOldObjectAlignmentOffset | kHeapObjectTag));
+  j(NOT_EQUAL, &done, Assembler::kNearJump);
+  Stop("Store buffer update is required");
+  Bind(&done);
+#endif
+}
+
+
+void Assembler::StoreIntoObjectNoBarrier(Register object,
+                                         const FieldAddress& dest,
+                                         const Immediate& value) {
+  movl(dest, value);

[srdjan, 2012/06/12 06:57:08]

I do not think this works as the inlined value is not marked to be an object. I
would pass a const Object& instead of const Immediate&

[cshapiro, 2012/06/12 21:41:01]

Thanks.  I have changed the code to use EmitObject.  I am reluctant to provide a
dual of "LoadObject" because any "StoreObject" must go through the write barrier
to preserve invariants needed by the garbage collector.  These seems a little
bit messy because it buries a MOV in the assembler code.  This is the assembler,
after all.  Maybe I am over-thinking this?

+  // No store buffer update.
+  int addr = value.value();
+  bool is_smi = ((addr & kHeapObjectTag) == 0);
+  bool is_old = ((addr & (kOldObjectAlignmentOffset | kHeapObjectTag)) == 1);
+  ASSERT(is_smi || is_old);
+}
+
+
 void Assembler::LoadDoubleConstant(XmmRegister dst, double value) {
   // TODO(5410843): Need to have a code constants table.
   int64_t constant = bit_cast<int64_t, double>(value);
   pushl(Immediate(Utils::High32Bits(constant)));
   pushl(Immediate(Utils::Low32Bits(constant)));
   movsd(dst, Address(ESP, 0));
   addl(ESP, Immediate(2 * kWordSize));
 }
 
 
@@ skipping 263 matching lines @@
     comments.SetCommentAt(i, comments_[i]->comment());
   }
 
   return comments;
 }
 
 
 }  // namespace dart
 
 #endif  // defined TARGET_ARCH_IA32