Deletion barrier: Distinguish+verify field initialization in ia32 generated code.

runtime/vm/flow_graph_optimizer.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/flow_graph_optimizer.h"
 
 #include "vm/bit_vector.h"
 #include "vm/cha.h"
 #include "vm/cpu.h"
 #include "vm/dart_entry.h"
@@ skipping 4486 matching lines @@
           break;
       }
     }
   }
 }
 
 
 void FlowGraphOptimizer::VisitStoreInstanceField(
     StoreInstanceFieldInstr* instr) {
   if (instr->IsUnboxedStore()) {
-    ASSERT(instr->is_initialization_);
+    ASSERT(instr->is_potential_unboxed_initialization_);
     // Determine if this field should be unboxed based on the usage of getter
     // and setter functions: The heuristic requires that the setter has a
     // usage count of at least 1/kGetterSetterRatio of the getter usage count.
     // This is to avoid unboxing fields where the setter is never or rarely
     // executed.
     const Field& field = Field::ZoneHandle(I, instr->field().raw());
     const String& field_name = String::Handle(I, field.name());
     const Class& owner = Class::Handle(I, field.owner());
     const Function& getter =
         Function::Handle(I, owner.LookupGetterFunction(field_name));
@@ skipping 24 matching lines @@
       new AllocateUninitializedContextInstr(instr->token_pos(),
                                             instr->num_context_variables());
   instr->ReplaceWith(replacement, current_iterator());
 
   StoreInstanceFieldInstr* store =
       new(I) StoreInstanceFieldInstr(Context::parent_offset(),
                                      new Value(replacement),
                                      new Value(flow_graph_->constant_null()),
                                      kNoStoreBarrier,
                                      instr->token_pos());
-  store->set_is_initialization(true);  // Won't be eliminated by DSE.
+  // Storing into uninitialized memory; remember to prevent dead store
+  // elimination and ensure proper GC barrier.
+  store->set_is_object_reference_initialization(true);
   flow_graph_->InsertAfter(replacement, store, NULL, FlowGraph::kEffect);
   Definition* cursor = store;
   for (intptr_t i = 0; i < instr->num_context_variables(); ++i) {
     store =
         new(I) StoreInstanceFieldInstr(Context::variable_offset(i),
                                        new Value(replacement),
                                        new Value(flow_graph_->constant_null()),
                                        kNoStoreBarrier,
                                        instr->token_pos());
-    store->set_is_initialization(true);  // Won't be eliminated by DSE.
+    // Storing into uninitialized memory; remember to prevent dead store
+    // elimination and ensure proper GC barrier.
+    store->set_is_object_reference_initialization(true);
     flow_graph_->InsertAfter(cursor, store, NULL, FlowGraph::kEffect);
     cursor = store;
   }
 }
 
 
 void FlowGraphOptimizer::VisitLoadCodeUnits(LoadCodeUnitsInstr* instr) {
   // TODO(zerny): Use kUnboxedUint32 once it is fully supported/optimized.
 #if defined(TARGET_ARCH_IA32) || defined(TARGET_ARCH_ARM)
   if (!instr->can_pack_into_smi())
@@ skipping 2552 matching lines @@
       Dump();
     }
     EliminateDeadStores();
     if (FLAG_trace_load_optimization) {
       FlowGraphPrinter::PrintGraph("After StoreOptimizer", graph_);
     }
   }
 
   bool CanEliminateStore(Instruction* instr) {
     switch (instr->tag()) {
-      case Instruction::kStoreInstanceField:
-        if (instr->AsStoreInstanceField()->is_initialization()) {
-          // Can't eliminate stores that initialized unboxed fields.
-          return false;
-        }
+      case Instruction::kStoreInstanceField: {
+        StoreInstanceFieldInstr* store_instance = instr->AsStoreInstanceField();
+        // Can't eliminate stores that initialize fields.
+        return !(store_instance->is_potential_unboxed_initialization() ||
+                 store_instance->is_object_reference_initialization());
+      }
       case Instruction::kStoreIndexed:
       case Instruction::kStoreStaticField:
         return true;
       default:
         UNREACHABLE();
         return false;
     }
   }
 
   virtual void ComputeInitialSets() {
@@ skipping 1312 matching lines @@
 
   // Insert materializations at environment uses.
   for (intptr_t i = 0; i < exits_collector_.exits().length(); i++) {
     CreateMaterializationAt(
         exits_collector_.exits()[i], alloc, *slots);
   }
 }
 
 
 }  // namespace dart