Improve redundant load elimination

runtime/vm/intermediate_language.h

 // Copyright (c) 2012, 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 924 matching lines @@
   // Returns -1 if pred is not in the list.
   intptr_t IndexOfPredecessor(BlockEntryInstr* pred) const;
 
   ZoneGrowableArray<PhiInstr*>* phis() const { return phis_; }
 
   virtual void PrepareEntry(FlowGraphCompiler* compiler);
 
   void InsertPhi(intptr_t var_index, intptr_t var_count);
   void RemoveDeadPhis();
 
+  void InsertPhi(PhiInstr* phi);
+
   intptr_t phi_count() const { return phi_count_; }
 
   virtual void PrintTo(BufferFormatter* f) const;
 
  private:
   friend class FlowGraph;  // Access to predecessors_ when inlining.
   virtual void ClearPredecessors() { predecessors_.Clear(); }
   virtual void AddPredecessor(BlockEntryInstr* predecessor);
 
   GrowableArray<BlockEntryInstr*> predecessors_;
@@ skipping 177 matching lines @@
 
   virtual void InferRange();
 
   Range* range() const { return range_; }
 
   // Definitions can be canonicalized only into definitions to ensure
   // this check statically we override base Canonicalize with a Canonicalize
   // returning Definition (return type is covariant).
   virtual Definition* Canonicalize(FlowGraphOptimizer* optimizer);
 
+  static const intptr_t kReplacementMarker = -2;
+
+  Definition* Replacement() {
+    if (ssa_temp_index_ == kReplacementMarker) {
+      return reinterpret_cast<Definition*>(temp_index_);
+    }
+    return this;
+  }
+
+  void SetReplacement(Definition* other) {
+    ASSERT(ssa_temp_index_ >= 0);
+    ASSERT(WasEliminated());
+    ssa_temp_index_ = kReplacementMarker;
+    temp_index_ = reinterpret_cast<intptr_t>(other);
+  }
+
  protected:
   friend class RangeAnalysis;
 
   Range* range_;
 
  private:
   intptr_t temp_index_;
   intptr_t ssa_temp_index_;
   // TODO(regis): GrowableArray<const AbstractType*> propagated_types_;
   // For now:
@@ skipping 3149 matching lines @@
   ForwardInstructionIterator* current_iterator_;
 
  private:
   DISALLOW_COPY_AND_ASSIGN(FlowGraphVisitor);
 };
 
 
 }  // namespace dart
 
 #endif  // VM_INTERMEDIATE_LANGUAGE_H_