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

runtime/vm/assembler_ia32.cc

Index: runtime/vm/assembler_ia32.cc
diff --git a/runtime/vm/assembler_ia32.cc b/runtime/vm/assembler_ia32.cc
index 9a6c5112f8c1b073b161dd32c56c0e8dfcc3c4a7..7c700b48a27ed4bc25b779fb7cfc536e052ca1c5 100644
--- a/runtime/vm/assembler_ia32.cc
+++ b/runtime/vm/assembler_ia32.cc
@@ -13,6 +13,8 @@
 
 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");
@@ -1364,8 +1366,54 @@ void Assembler::CompareObject(Register reg, const Object& 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);
 }