First implementation of allocation elimination in Hydrogen.

src/lithium.h

 // Copyright 2012 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 515 matching lines @@
         arguments_stack_height_(argument_count),
         deoptimization_index_(Safepoint::kNoDeoptimizationIndex),
         translation_index_(-1),
         ast_id_(ast_id),
         translation_size_(value_count),
         parameter_count_(parameter_count),
         pc_offset_(-1),
         values_(value_count, zone),
         is_tagged_(value_count, zone),
         is_uint32_(value_count, zone),
+        object_mapping_(0, zone),
         outer_(outer),
         entry_(entry),
         zone_(zone) { }
 
   Handle<JSFunction> closure() const { return closure_; }
   FrameType frame_type() const { return frame_type_; }
   int arguments_stack_height() const { return arguments_stack_height_; }
   int deoptimization_index() const { return deoptimization_index_; }
   int translation_index() const { return translation_index_; }
   BailoutId ast_id() const { return ast_id_; }
@@ skipping 20 matching lines @@
   }
 
   bool HasTaggedValueAt(int index) const {
     return is_tagged_.Contains(index);
   }
 
   bool HasUint32ValueAt(int index) const {
     return is_uint32_.Contains(index);
   }
 
+  void AddNewObject(int length, bool is_arguments) {
+    uint32_t encoded = LengthOrDupeField::encode(length) |
+                       IsArgumentsField::encode(is_arguments) |
+                       IsDuplicateField::encode(false);
+    object_mapping_.Add(encoded, zone());
+  }
+
+  void AddDuplicateObject(int dupe_of) {
+    uint32_t encoded = LengthOrDupeField::encode(dupe_of) |
+                       IsDuplicateField::encode(true);
+    object_mapping_.Add(encoded, zone());
+  }
+
+  int ObjectDuplicateOfAt(int index) {
+    ASSERT(ObjectIsDuplicateAt(index));
+    return LengthOrDupeField::decode(object_mapping_[index]);
+  }
+
+  int ObjectLengthAt(int index) {
+    ASSERT(!ObjectIsDuplicateAt(index));
+    return LengthOrDupeField::decode(object_mapping_[index]);
+  }
+
+  bool ObjectIsArgumentsAt(int index) {
+    ASSERT(!ObjectIsDuplicateAt(index));
+    return IsArgumentsField::decode(object_mapping_[index]);
+  }
+
+  bool ObjectIsDuplicateAt(int index) {
+    return IsDuplicateField::decode(object_mapping_[index]);
+  }
+
   void Register(int deoptimization_index,
                 int translation_index,
                 int pc_offset) {
     ASSERT(!HasBeenRegistered());
     deoptimization_index_ = deoptimization_index;
     translation_index_ = translation_index;
     pc_offset_ = pc_offset;
   }
   bool HasBeenRegistered() const {
     return deoptimization_index_ != Safepoint::kNoDeoptimizationIndex;
   }
 
   void PrintTo(StringStream* stream);
 
+  // Marker value indicating a de-materialized object.
+  static LOperand* materialization_marker() { return NULL; }

[titzer, 2013/08/01 17:11:50]

NULL seems like it could get mixed up sometime. Maybe -1?

[Michael Starzinger, 2013/08/05 15:13:00]

That would require many changes in the register allocator, because NULL is the
only LOperand being skipped there. We can do that, but I would very much like to
do that in another CL, not as part of this one.

+
+  // Encoding used for the object_mapping map below.
+  class LengthOrDupeField : public BitField<int,   0, 30> { };
+  class IsArgumentsField  : public BitField<bool, 30,  1> { };
+  class IsDuplicateField  : public BitField<bool, 31,  1> { };
+
  private:
   Handle<JSFunction> closure_;
   FrameType frame_type_;
   int arguments_stack_height_;
   int deoptimization_index_;
   int translation_index_;
   BailoutId ast_id_;
   int translation_size_;
   int parameter_count_;
   int pc_offset_;
 
   // Value array: [parameters] [locals] [expression stack] [de-materialized].
   //              |>--------- translation_size ---------<|
   ZoneList<LOperand*> values_;
   GrowableBitVector is_tagged_;
   GrowableBitVector is_uint32_;
+
+  // Map with encoded information about kMaterializationMarker operands.
+  ZoneList<uint32_t> object_mapping_;
+
   LEnvironment* outer_;
   HEnterInlined* entry_;
   Zone* zone_;
 };
 
 
 // Iterates over the non-null, non-constant operands in an environment.
 class ShallowIterator BASE_EMBEDDED {
  public:
   explicit ShallowIterator(LEnvironment* env)
@@ skipping 153 matching lines @@
  private:
   LChunk* chunk_;
 
   DISALLOW_COPY_AND_ASSIGN(LPhase);
 };
 
 
 } }  // namespace v8::internal
 
 #endif  // V8_LITHIUM_H_