Implement a branch optimization pass.

runtime/vm/intermediate_language.h

 // 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.
 
 #ifndef VM_INTERMEDIATE_LANGUAGE_H_
 #define VM_INTERMEDIATE_LANGUAGE_H_
 
 #include "vm/allocation.h"
 #include "vm/ast.h"
 #include "vm/growable_array.h"
@@ skipping 545 matching lines @@
   Instruction* previous() const { return previous_; }
   void set_previous(Instruction* instr) {
     ASSERT(!IsBlockEntry());
     previous_ = instr;
   }
 
   Instruction* next() const { return next_; }
   void set_next(Instruction* instr) {
     ASSERT(!IsGraphEntry());
     ASSERT(!IsReturn());
-    ASSERT(!IsControl());
+    ASSERT(!IsControl() || (instr == NULL));
     ASSERT(!IsPhi());
     ASSERT(instr == NULL || !instr->IsBlockEntry());
     // TODO(fschneider): Also add Throw and ReThrow to the list of instructions
     // that do not have a successor. Currently, the graph builder will continue
     // to append instruction in case of a Throw inside an expression. This
     // condition should be handled in the graph builder
     next_ = instr;
   }
 
   // Link together two instruction.
@@ skipping 728 matching lines @@
       *type_ = new_type;
       return true;
     }
 
     return false;
   }
 
   bool HasUses() const {
     return (input_use_list_ != NULL) || (env_use_list_ != NULL);
   }
+  bool HasOnlyUse(Value* use) const;
 
   Value* input_use_list() const { return input_use_list_; }
   void set_input_use_list(Value* head) { input_use_list_ = head; }
 
   Value* env_use_list() const { return env_use_list_; }
   void set_env_use_list(Value* head) { env_use_list_ = head; }
 
   void AddInputUse(Value* value) { Value::AddToList(value, &input_use_list_); }
   void AddEnvUse(Value* value) { Value::AddToList(value, &env_use_list_); }
 
@@ skipping 701 matching lines @@
 
 
 class ConstantInstr : public TemplateDefinition<0> {
  public:
   explicit ConstantInstr(const Object& value)
       : value_(value) { }
 
   DECLARE_INSTRUCTION(Constant)
   virtual CompileType ComputeType() const;
 
+  virtual Definition* Canonicalize(FlowGraphOptimizer* optimizer);
+
   const Object& value() const { return value_; }
 
   virtual void PrintOperandsTo(BufferFormatter* f) const;
 
   virtual bool CanDeoptimize() const { return false; }
 
   virtual bool HasSideEffect() const { return false; }
 
   virtual bool AttributesEqual(Instruction* other) const;
   virtual bool AffectedBySideEffect() const { return false; }
@@ skipping 2453 matching lines @@
   ForwardInstructionIterator* current_iterator_;
 
  private:
   DISALLOW_COPY_AND_ASSIGN(FlowGraphVisitor);
 };
 
 
 }  // namespace dart
 
 #endif  // VM_INTERMEDIATE_LANGUAGE_H_