Basic array capacity feedback via allocation sites.

src/objects.h

 // Copyright 2012 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef V8_OBJECTS_H_
 #define V8_OBJECTS_H_
 
 #include <iosfwd>
 
 #include "src/allocation.h"
@@ skipping 8134 matching lines @@
   DECL_ACCESSORS(dependent_code, DependentCode)
   DECL_ACCESSORS(weak_next, Object)
 
   inline void Initialize();
 
   // This method is expensive, it should only be called for reporting.
   bool IsNestedSite();
 
   // transition_info bitfields, for constructed array transition info.
   class ElementsKindBits:       public BitField<ElementsKind, 0,  15> {};
-  class UnusedBits:             public BitField<int,          15, 14> {};
+  class InitialElementsCapacity : public BitField<int, 15, 10> {};
+  class UnusedBits : public BitField<int, 25, 4> {};
   class DoNotInlineBit:         public BitField<bool,         29,  1> {};
 
   // Bitfields for pretenure_data
   class MementoFoundCountBits:  public BitField<int,               0, 26> {};
   class PretenureDecisionBits:  public BitField<PretenureDecision, 26, 3> {};
   class DeoptDependentCodeBit:  public BitField<bool,              29, 1> {};
   STATIC_ASSERT(PretenureDecisionBits::kMax >= kLastPretenureDecisionValue);
 
   // Increments the mementos found counter and returns true when the first
   // memento was found for a given allocation site.
@@ skipping 69 matching lines @@
     int value = Smi::cast(transition_info())->value();
     return ElementsKindBits::decode(value);
   }
 
   void SetElementsKind(ElementsKind kind) {
     int value = Smi::cast(transition_info())->value();
     set_transition_info(Smi::FromInt(ElementsKindBits::update(value, kind)),
                         SKIP_WRITE_BARRIER);
   }
 
+  inline int GetInitialElementsCapacity();
+
+  // Note that the function accepts the new length, not capacity.
+  inline void DigestInitialElementsCapacityFeedback(int new_length);
+
   bool CanInlineCall() {
     int value = Smi::cast(transition_info())->value();
     return DoNotInlineBit::decode(value) == 0;
   }
 
   void SetDoNotInlineCall() {
     int value = Smi::cast(transition_info())->value();
     set_transition_info(Smi::FromInt(DoNotInlineBit::update(value, true)),
                         SKIP_WRITE_BARRIER);
   }
@@ skipping 1839 matching lines @@
   // Expand the fixed array backing of a fast-case JSArray to at least
   // the requested size.
   static void Expand(Handle<JSArray> array,
                      int minimum_size_of_backing_fixed_array);
 
   // Dispatched behavior.
   DECLARE_PRINTER(JSArray)
   DECLARE_VERIFIER(JSArray)
 
   // Number of element slots to pre-allocate for an empty array.
-  static const int kPreallocatedArrayElements = 4;
+  static int PreallocatedArrayElements() {
+    if (FLAG_initial_capacity_mode == 1) return 4;
+    DCHECK(FLAG_initial_capacity_mode == 0 ||
+           FLAG_initial_capacity_mode == 2);
+    return 0;
+  }
 
   // Layout description.
   static const int kLengthOffset = JSObject::kHeaderSize;
   static const int kSize = kLengthOffset + kPointerSize;
 
  private:
   DISALLOW_IMPLICIT_CONSTRUCTORS(JSArray);
 };
 
 
@@ skipping 726 matching lines @@
     } else {
       value &= ~(1 << bit_position);
     }
     return value;
   }
 };
 
 } }  // namespace v8::internal
 
 #endif  // V8_OBJECTS_H_