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      1 // Copyright 2012 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 #include "src/elements-kind.h"
      6 
      7 #include "src/api.h"
      8 #include "src/base/lazy-instance.h"
      9 #include "src/elements.h"
     10 #include "src/objects.h"
     11 
     12 namespace v8 {
     13 namespace internal {
     14 
     15 
     16 int ElementsKindToShiftSize(ElementsKind elements_kind) {
     17   switch (elements_kind) {
     18     case UINT8_ELEMENTS:
     19     case INT8_ELEMENTS:
     20     case UINT8_CLAMPED_ELEMENTS:
     21       return 0;
     22     case UINT16_ELEMENTS:
     23     case INT16_ELEMENTS:
     24       return 1;
     25     case UINT32_ELEMENTS:
     26     case INT32_ELEMENTS:
     27     case FLOAT32_ELEMENTS:
     28       return 2;
     29     case FAST_DOUBLE_ELEMENTS:
     30     case FAST_HOLEY_DOUBLE_ELEMENTS:
     31     case FLOAT64_ELEMENTS:
     32       return 3;
     33     case FAST_SMI_ELEMENTS:
     34     case FAST_ELEMENTS:
     35     case FAST_HOLEY_SMI_ELEMENTS:
     36     case FAST_HOLEY_ELEMENTS:
     37     case DICTIONARY_ELEMENTS:
     38     case FAST_SLOPPY_ARGUMENTS_ELEMENTS:
     39     case SLOW_SLOPPY_ARGUMENTS_ELEMENTS:
     40       return kPointerSizeLog2;
     41   }
     42   UNREACHABLE();
     43   return 0;
     44 }
     45 
     46 
     47 int GetDefaultHeaderSizeForElementsKind(ElementsKind elements_kind) {
     48   STATIC_ASSERT(FixedArray::kHeaderSize == FixedDoubleArray::kHeaderSize);
     49 
     50   if (IsFixedTypedArrayElementsKind(elements_kind)) {
     51     return 0;
     52   } else {
     53     return FixedArray::kHeaderSize - kHeapObjectTag;
     54   }
     55 }
     56 
     57 
     58 const char* ElementsKindToString(ElementsKind kind) {
     59   ElementsAccessor* accessor = ElementsAccessor::ForKind(kind);
     60   return accessor->name();
     61 }
     62 
     63 
     64 struct InitializeFastElementsKindSequence {
     65   static void Construct(
     66       ElementsKind** fast_elements_kind_sequence_ptr) {
     67     ElementsKind* fast_elements_kind_sequence =
     68         new ElementsKind[kFastElementsKindCount];
     69     *fast_elements_kind_sequence_ptr = fast_elements_kind_sequence;
     70     STATIC_ASSERT(FAST_SMI_ELEMENTS == FIRST_FAST_ELEMENTS_KIND);
     71     fast_elements_kind_sequence[0] = FAST_SMI_ELEMENTS;
     72     fast_elements_kind_sequence[1] = FAST_HOLEY_SMI_ELEMENTS;
     73     fast_elements_kind_sequence[2] = FAST_DOUBLE_ELEMENTS;
     74     fast_elements_kind_sequence[3] = FAST_HOLEY_DOUBLE_ELEMENTS;
     75     fast_elements_kind_sequence[4] = FAST_ELEMENTS;
     76     fast_elements_kind_sequence[5] = FAST_HOLEY_ELEMENTS;
     77 
     78     // Verify that kFastElementsKindPackedToHoley is correct.
     79     STATIC_ASSERT(FAST_SMI_ELEMENTS + kFastElementsKindPackedToHoley ==
     80                   FAST_HOLEY_SMI_ELEMENTS);
     81     STATIC_ASSERT(FAST_DOUBLE_ELEMENTS + kFastElementsKindPackedToHoley ==
     82                   FAST_HOLEY_DOUBLE_ELEMENTS);
     83     STATIC_ASSERT(FAST_ELEMENTS + kFastElementsKindPackedToHoley ==
     84                   FAST_HOLEY_ELEMENTS);
     85   }
     86 };
     87 
     88 
     89 static base::LazyInstance<ElementsKind*,
     90                           InitializeFastElementsKindSequence>::type
     91     fast_elements_kind_sequence = LAZY_INSTANCE_INITIALIZER;
     92 
     93 
     94 ElementsKind GetFastElementsKindFromSequenceIndex(int sequence_number) {
     95   DCHECK(sequence_number >= 0 &&
     96          sequence_number < kFastElementsKindCount);
     97   return fast_elements_kind_sequence.Get()[sequence_number];
     98 }
     99 
    100 
    101 int GetSequenceIndexFromFastElementsKind(ElementsKind elements_kind) {
    102   for (int i = 0; i < kFastElementsKindCount; ++i) {
    103     if (fast_elements_kind_sequence.Get()[i] == elements_kind) {
    104       return i;
    105     }
    106   }
    107   UNREACHABLE();
    108   return 0;
    109 }
    110 
    111 
    112 ElementsKind GetNextTransitionElementsKind(ElementsKind kind) {
    113   int index = GetSequenceIndexFromFastElementsKind(kind);
    114   return GetFastElementsKindFromSequenceIndex(index + 1);
    115 }
    116 
    117 
    118 static inline bool IsFastTransitionTarget(ElementsKind elements_kind) {
    119   return IsFastElementsKind(elements_kind) ||
    120       elements_kind == DICTIONARY_ELEMENTS;
    121 }
    122 
    123 bool IsMoreGeneralElementsKindTransition(ElementsKind from_kind,
    124                                          ElementsKind to_kind) {
    125   if (IsFixedTypedArrayElementsKind(from_kind) ||
    126       IsFixedTypedArrayElementsKind(to_kind)) {
    127     return false;
    128   }
    129   if (IsFastElementsKind(from_kind) && IsFastTransitionTarget(to_kind)) {
    130     switch (from_kind) {
    131       case FAST_SMI_ELEMENTS:
    132         return to_kind != FAST_SMI_ELEMENTS;
    133       case FAST_HOLEY_SMI_ELEMENTS:
    134         return to_kind != FAST_SMI_ELEMENTS &&
    135             to_kind != FAST_HOLEY_SMI_ELEMENTS;
    136       case FAST_DOUBLE_ELEMENTS:
    137         return to_kind != FAST_SMI_ELEMENTS &&
    138             to_kind != FAST_HOLEY_SMI_ELEMENTS &&
    139             to_kind != FAST_DOUBLE_ELEMENTS;
    140       case FAST_HOLEY_DOUBLE_ELEMENTS:
    141         return to_kind == FAST_ELEMENTS ||
    142             to_kind == FAST_HOLEY_ELEMENTS;
    143       case FAST_ELEMENTS:
    144         return to_kind == FAST_HOLEY_ELEMENTS;
    145       case FAST_HOLEY_ELEMENTS:
    146         return false;
    147       default:
    148         return false;
    149     }
    150   }
    151   return false;
    152 }
    153 
    154 
    155 }  // namespace internal
    156 }  // namespace v8
    157