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      1 // Copyright 2014 the V8 project authors. All rights reserved.
      2 // Use of this source code is governed by a BSD-style license that can be
      3 // found in the LICENSE file.
      4 
      5 #ifndef V8_FIELD_INDEX_H_
      6 #define V8_FIELD_INDEX_H_
      7 
      8 #include "src/property-details.h"
      9 #include "src/utils.h"
     10 
     11 namespace v8 {
     12 namespace internal {
     13 
     14 class Map;
     15 
     16 // Wrapper class to hold a field index, usually but not necessarily generated
     17 // from a property index. When available, the wrapper class captures additional
     18 // information to allow the field index to be translated back into the property
     19 // index it was originally generated from.
     20 class FieldIndex final {
     21  public:
     22   enum Encoding { kTagged, kDouble, kWord32 };
     23 
     24   FieldIndex() : bit_field_(0) {}
     25 
     26   static FieldIndex ForPropertyIndex(
     27       const Map* map, int index,
     28       Representation representation = Representation::Tagged());
     29   static FieldIndex ForInObjectOffset(int offset, Encoding encoding,
     30                                       const Map* map = nullptr);
     31   static FieldIndex ForDescriptor(const Map* map, int descriptor_index);
     32 
     33   int GetLoadByFieldIndex() const;
     34 
     35   bool is_inobject() const {
     36     return IsInObjectBits::decode(bit_field_);
     37   }
     38 
     39   bool is_hidden_field() const { return IsHiddenField::decode(bit_field_); }
     40 
     41   bool is_double() const { return EncodingBits::decode(bit_field_) == kDouble; }
     42 
     43   int offset() const { return OffsetBits::decode(bit_field_); }
     44 
     45   // Zero-indexed from beginning of the object.
     46   int index() const {
     47     DCHECK_EQ(0, offset() % kPointerSize);
     48     return offset() / kPointerSize;
     49   }
     50 
     51   int outobject_array_index() const {
     52     DCHECK(!is_inobject());
     53     return index() - first_inobject_property_offset() / kPointerSize;
     54   }
     55 
     56   // Zero-based from the first inobject property. Overflows to out-of-object
     57   // properties.
     58   int property_index() const {
     59     DCHECK(!is_hidden_field());
     60     int result = index() - first_inobject_property_offset() / kPointerSize;
     61     if (!is_inobject()) {
     62       result += InObjectPropertyBits::decode(bit_field_);
     63     }
     64     return result;
     65   }
     66 
     67   int GetFieldAccessStubKey() const {
     68     return bit_field_ &
     69            (IsInObjectBits::kMask | EncodingBits::kMask | OffsetBits::kMask);
     70   }
     71 
     72   bool operator==(FieldIndex const& other) const {
     73     return bit_field_ == other.bit_field_;
     74   }
     75   bool operator!=(FieldIndex const& other) const { return !(*this == other); }
     76 
     77  private:
     78   FieldIndex(bool is_inobject, int offset, Encoding encoding,
     79              int inobject_properties, int first_inobject_property_offset,
     80              bool is_hidden = false) {
     81     DCHECK_EQ(first_inobject_property_offset & (kPointerSize - 1), 0);
     82     bit_field_ = IsInObjectBits::encode(is_inobject) |
     83                  EncodingBits::encode(encoding) |
     84                  FirstInobjectPropertyOffsetBits::encode(
     85                      first_inobject_property_offset) |
     86                  IsHiddenField::encode(is_hidden) | OffsetBits::encode(offset) |
     87                  InObjectPropertyBits::encode(inobject_properties);
     88   }
     89 
     90   static Encoding FieldEncoding(Representation representation) {
     91     switch (representation.kind()) {
     92       case Representation::kNone:
     93       case Representation::kSmi:
     94       case Representation::kHeapObject:
     95       case Representation::kTagged:
     96         return kTagged;
     97       case Representation::kDouble:
     98         return kDouble;
     99       default:
    100         break;
    101     }
    102     PrintF("%s\n", representation.Mnemonic());
    103     UNREACHABLE();
    104     return kTagged;
    105   }
    106 
    107   int first_inobject_property_offset() const {
    108     DCHECK(!is_hidden_field());
    109     return FirstInobjectPropertyOffsetBits::decode(bit_field_);
    110   }
    111 
    112   static const int kOffsetBitsSize =
    113       (kDescriptorIndexBitCount + 1 + kPointerSizeLog2);
    114 
    115   // Index from beginning of object.
    116   class OffsetBits : public BitField64<int, 0, kOffsetBitsSize> {};
    117   class IsInObjectBits : public BitField64<bool, OffsetBits::kNext, 1> {};
    118   class EncodingBits : public BitField64<Encoding, IsInObjectBits::kNext, 2> {};
    119   // Number of inobject properties.
    120   class InObjectPropertyBits
    121       : public BitField64<int, EncodingBits::kNext, kDescriptorIndexBitCount> {
    122   };
    123   // Offset of first inobject property from beginning of object.
    124   class FirstInobjectPropertyOffsetBits
    125       : public BitField64<int, InObjectPropertyBits::kNext,
    126                           kFirstInobjectPropertyOffsetBitCount> {};
    127   class IsHiddenField
    128       : public BitField64<bool, FirstInobjectPropertyOffsetBits::kNext, 1> {};
    129   STATIC_ASSERT(IsHiddenField::kNext <= 64);
    130 
    131   uint64_t bit_field_;
    132 };
    133 
    134 }  // namespace internal
    135 }  // namespace v8
    136 
    137 #endif  // V8_FIELD_INDEX_H_
    138