Remove dead phis as soon as they are discovered.

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 1101 matching lines @@
 
   DISALLOW_COPY_AND_ASSIGN(GraphEntryInstr);
 };
 
 
 class JoinEntryInstr : public BlockEntryInstr {
  public:
   JoinEntryInstr(intptr_t block_id, intptr_t try_index)
       : BlockEntryInstr(block_id, try_index),
         predecessors_(2),  // Two is the assumed to be the common case.
-        phis_(NULL),
-        phi_count_(0) { }
+        phis_(NULL) { }
 
   DECLARE_INSTRUCTION(JoinEntry)
 
   virtual intptr_t PredecessorCount() const { return predecessors_.length(); }
   virtual BlockEntryInstr* PredecessorAt(intptr_t index) const {
     return predecessors_[index];
   }
 
   // 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 RemoveDeadPhis(Definition* replacement);
 
   void InsertPhi(PhiInstr* phi);
 
-  intptr_t phi_count() const { return phi_count_; }
-
   virtual void PrintTo(BufferFormatter* f) const;
 
  private:
   // Classes that have access to predecessors_ when inlining.
   friend class BlockEntryInstr;
   friend class ValueInliningContext;
 
+  // Direct access to phis_ in order to resize it due to phi elimination.
+  friend class ConstantPropagator;
+
   virtual void ClearPredecessors() { predecessors_.Clear(); }
   virtual void AddPredecessor(BlockEntryInstr* predecessor);
 
   GrowableArray<BlockEntryInstr*> predecessors_;
   ZoneGrowableArray<PhiInstr*>* phis_;
-  intptr_t phi_count_;
 
   DISALLOW_COPY_AND_ASSIGN(JoinEntryInstr);
 };
 
 
 class PhiIterator : public ValueObject {
  public:
   explicit PhiIterator(JoinEntryInstr* join)
-      : phis_(join->phis()), index_(-1) {
-    if (!Done()) Advance();  // Advance to the first phi.
-  }
+      : phis_(join->phis()), index_(0) { }
 
   void Advance() {
     ASSERT(!Done());
-    do {
-      index_++;
-    } while (!Done() && (Current() == NULL));
+    index_++;
   }
 
   bool Done() const {
     return (phis_ == NULL) || (index_ >= phis_->length());
   }
 
   PhiInstr* Current() const {
     return (*phis_)[index_];
   }
 
@@ skipping 3308 matching lines @@
   ForwardInstructionIterator* current_iterator_;
 
  private:
   DISALLOW_COPY_AND_ASSIGN(FlowGraphVisitor);
 };
 
 
 }  // namespace dart
 
 #endif  // VM_INTERMEDIATE_LANGUAGE_H_