Use type propagation to eliminate store barriers.

runtime/vm/intermediate_language_x64.cc

Index: runtime/vm/intermediate_language_x64.cc
===================================================================
--- runtime/vm/intermediate_language_x64.cc	(revision 11354)
+++ runtime/vm/intermediate_language_x64.cc	(working copy)
@@ -920,12 +920,12 @@
       __ j(ABOVE_EQUAL, deopt);
       // Note that index is Smi, i.e, times 4.
       ASSERT(kSmiTagShift == 1);
-      if (this->value()->BindsToConstant()) {
-        // Compile time constants are Smi or allocated in the old space.
-        __ movq(FieldAddress(receiver, index, TIMES_4, sizeof(RawArray)),
+      if (this->value()->NeedsStoreBuffer()) {
+        __ StoreIntoObject(receiver,
+            FieldAddress(receiver, index, TIMES_4, sizeof(RawArray)),
             value);
       } else {
-        __ StoreIntoObject(receiver,
+        __ StoreIntoObjectNoBarrier(receiver,
             FieldAddress(receiver, index, TIMES_4, sizeof(RawArray)),
             value);
       }
@@ -939,12 +939,12 @@
       __ movq(temp, FieldAddress(receiver, GrowableObjectArray::data_offset()));
       // Note that index is Smi, i.e, times 4.
       ASSERT(kSmiTagShift == 1);
-      if (this->value()->BindsToConstant()) {
-        // Compile time constants are Smi or allocated in the old space.
-        __ movq(FieldAddress(temp, index, TIMES_4, sizeof(RawArray)),
+      if (this->value()->NeedsStoreBuffer()) {
+        __ StoreIntoObject(temp,
+            FieldAddress(temp, index, TIMES_4, sizeof(RawArray)),
             value);
       } else {
-        __ StoreIntoObject(temp,
+        __ StoreIntoObjectNoBarrier(temp,
             FieldAddress(temp, index, TIMES_4, sizeof(RawArray)),
             value);
       }
@@ -1018,12 +1018,12 @@
     ASSERT(ic_data() != NULL);
     compiler->EmitClassChecksNoSmi(*ic_data(), instance_reg, temp_reg, deopt);
   }
-  if (this->value()->BindsToConstant()) {
-    // Compile time constants are Smi or allocated in the old space.
-    __ movq(FieldAddress(instance_reg, field().Offset()), value_reg);
-  } else {
+  if (this->value()->NeedsStoreBuffer()) {
     __ StoreIntoObject(instance_reg,
         FieldAddress(instance_reg, field().Offset()), value_reg);
+  } else {
+    __ StoreIntoObjectNoBarrier(instance_reg,
+        FieldAddress(instance_reg, field().Offset()), value_reg);
   }
 }
 
@@ -1057,11 +1057,11 @@
   ASSERT(locs()->out().reg() == value);
 
   __ LoadObject(temp, field());
-  if (this->value()->BindsToConstant()) {
-    // Compile time constants are Smi or allocated in the old space.
-    __ movq(FieldAddress(temp, Field::value_offset()), value);
+  if (this->value()->NeedsStoreBuffer()) {
+    __ StoreIntoObject(temp, FieldAddress(temp, Field::value_offset()), value);
   } else {
-    __ StoreIntoObject(temp, FieldAddress(temp, Field::value_offset()), value);
+    __ StoreIntoObjectNoBarrier(
+        temp, FieldAddress(temp, Field::value_offset()), value);
   }
 }