Heuristically predict interference on the back edge and use it to minimize number of register reshu…

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 1144 matching lines @@
   DISALLOW_COPY_AND_ASSIGN(Definition);
 };
 
 
 class PhiInstr : public Definition {
  public:
   explicit PhiInstr(JoinEntryInstr* block, intptr_t num_inputs)
     : block_(block),
       inputs_(num_inputs),
       is_alive_(false),
-      representation_(kTagged) {
+      representation_(kTagged),
+      reaching_defs_(NULL) {
     for (intptr_t i = 0; i < num_inputs; ++i) {
       inputs_.Add(NULL);
     }
   }
 
   // Get the block entry for that instruction.
   virtual BlockEntryInstr* GetBlock() const { return block(); }
   JoinEntryInstr* block() const { return block_; }
 
   virtual RawAbstractType* CompileType() const;
@@ skipping 40 matching lines @@
     UNREACHABLE();
     return kIllegalCid;
   }
 
   DECLARE_INSTRUCTION(Phi)
 
   virtual void PrintTo(BufferFormatter* f) const;
 
   virtual void InferRange();
 
+  BitVector* reaching_defs() const {
+    return reaching_defs_;
+  }
+
+  void set_reaching_defs(BitVector* reaching_defs) {
+    reaching_defs_ = reaching_defs;
+  }
+
  private:
   friend class ConstantPropagator;  // Direct access to inputs_.
 
   JoinEntryInstr* block_;
   GrowableArray<Value*> inputs_;
   bool is_alive_;
   Representation representation_;
 
+  BitVector* reaching_defs_;
+
   DISALLOW_COPY_AND_ASSIGN(PhiInstr);
 };
 
 
 class ParameterInstr : public Definition {
  public:
   explicit ParameterInstr(intptr_t index, GraphEntryInstr* block)
       : index_(index), block_(block) { }
 
   DECLARE_INSTRUCTION(Parameter)
@@ skipping 2997 matching lines @@
   ForwardInstructionIterator* current_iterator_;
 
  private:
   DISALLOW_COPY_AND_ASSIGN(FlowGraphVisitor);
 };
 
 
 }  // namespace dart
 
 #endif  // VM_INTERMEDIATE_LANGUAGE_H_