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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-inl.h"
     11 #include "src/objects.h"
     12 
     13 namespace v8 {
     14 namespace internal {
     15 
     16 
     17 int ElementsKindToShiftSize(ElementsKind elements_kind) {
     18   switch (elements_kind) {
     19     case UINT8_ELEMENTS:
     20     case INT8_ELEMENTS:
     21     case UINT8_CLAMPED_ELEMENTS:
     22       return 0;
     23     case UINT16_ELEMENTS:
     24     case INT16_ELEMENTS:
     25       return 1;
     26     case UINT32_ELEMENTS:
     27     case INT32_ELEMENTS:
     28     case FLOAT32_ELEMENTS:
     29       return 2;
     30     case FAST_DOUBLE_ELEMENTS:
     31     case FAST_HOLEY_DOUBLE_ELEMENTS:
     32     case FLOAT64_ELEMENTS:
     33       return 3;
     34     case FAST_SMI_ELEMENTS:
     35     case FAST_ELEMENTS:
     36     case FAST_HOLEY_SMI_ELEMENTS:
     37     case FAST_HOLEY_ELEMENTS:
     38     case DICTIONARY_ELEMENTS:
     39     case FAST_SLOPPY_ARGUMENTS_ELEMENTS:
     40     case SLOW_SLOPPY_ARGUMENTS_ELEMENTS:
     41     case FAST_STRING_WRAPPER_ELEMENTS:
     42     case SLOW_STRING_WRAPPER_ELEMENTS:
     43       return kPointerSizeLog2;
     44     case NO_ELEMENTS:
     45       UNREACHABLE();
     46       return 0;
     47   }
     48   UNREACHABLE();
     49   return 0;
     50 }
     51 
     52 
     53 int GetDefaultHeaderSizeForElementsKind(ElementsKind elements_kind) {
     54   STATIC_ASSERT(FixedArray::kHeaderSize == FixedDoubleArray::kHeaderSize);
     55 
     56   if (IsFixedTypedArrayElementsKind(elements_kind)) {
     57     return 0;
     58   } else {
     59     return FixedArray::kHeaderSize - kHeapObjectTag;
     60   }
     61 }
     62 
     63 
     64 const char* ElementsKindToString(ElementsKind kind) {
     65   ElementsAccessor* accessor = ElementsAccessor::ForKind(kind);
     66   return accessor->name();
     67 }
     68 
     69 
     70 struct InitializeFastElementsKindSequence {
     71   static void Construct(
     72       ElementsKind** fast_elements_kind_sequence_ptr) {
     73     ElementsKind* fast_elements_kind_sequence =
     74         new ElementsKind[kFastElementsKindCount];
     75     *fast_elements_kind_sequence_ptr = fast_elements_kind_sequence;
     76     STATIC_ASSERT(FAST_SMI_ELEMENTS == FIRST_FAST_ELEMENTS_KIND);
     77     fast_elements_kind_sequence[0] = FAST_SMI_ELEMENTS;
     78     fast_elements_kind_sequence[1] = FAST_HOLEY_SMI_ELEMENTS;
     79     fast_elements_kind_sequence[2] = FAST_DOUBLE_ELEMENTS;
     80     fast_elements_kind_sequence[3] = FAST_HOLEY_DOUBLE_ELEMENTS;
     81     fast_elements_kind_sequence[4] = FAST_ELEMENTS;
     82     fast_elements_kind_sequence[5] = FAST_HOLEY_ELEMENTS;
     83 
     84     // Verify that kFastElementsKindPackedToHoley is correct.
     85     STATIC_ASSERT(FAST_SMI_ELEMENTS + kFastElementsKindPackedToHoley ==
     86                   FAST_HOLEY_SMI_ELEMENTS);
     87     STATIC_ASSERT(FAST_DOUBLE_ELEMENTS + kFastElementsKindPackedToHoley ==
     88                   FAST_HOLEY_DOUBLE_ELEMENTS);
     89     STATIC_ASSERT(FAST_ELEMENTS + kFastElementsKindPackedToHoley ==
     90                   FAST_HOLEY_ELEMENTS);
     91   }
     92 };
     93 
     94 
     95 static base::LazyInstance<ElementsKind*,
     96                           InitializeFastElementsKindSequence>::type
     97     fast_elements_kind_sequence = LAZY_INSTANCE_INITIALIZER;
     98 
     99 
    100 ElementsKind GetFastElementsKindFromSequenceIndex(int sequence_number) {
    101   DCHECK(sequence_number >= 0 &&
    102          sequence_number < kFastElementsKindCount);
    103   return fast_elements_kind_sequence.Get()[sequence_number];
    104 }
    105 
    106 
    107 int GetSequenceIndexFromFastElementsKind(ElementsKind elements_kind) {
    108   for (int i = 0; i < kFastElementsKindCount; ++i) {
    109     if (fast_elements_kind_sequence.Get()[i] == elements_kind) {
    110       return i;
    111     }
    112   }
    113   UNREACHABLE();
    114   return 0;
    115 }
    116 
    117 
    118 ElementsKind GetNextTransitionElementsKind(ElementsKind kind) {
    119   int index = GetSequenceIndexFromFastElementsKind(kind);
    120   return GetFastElementsKindFromSequenceIndex(index + 1);
    121 }
    122 
    123 
    124 static inline bool IsFastTransitionTarget(ElementsKind elements_kind) {
    125   return IsFastElementsKind(elements_kind) ||
    126       elements_kind == DICTIONARY_ELEMENTS;
    127 }
    128 
    129 bool IsMoreGeneralElementsKindTransition(ElementsKind from_kind,
    130                                          ElementsKind to_kind) {
    131   if (IsFixedTypedArrayElementsKind(from_kind) ||
    132       IsFixedTypedArrayElementsKind(to_kind)) {
    133     return false;
    134   }
    135   if (IsFastElementsKind(from_kind) && IsFastTransitionTarget(to_kind)) {
    136     switch (from_kind) {
    137       case FAST_SMI_ELEMENTS:
    138         return to_kind != FAST_SMI_ELEMENTS;
    139       case FAST_HOLEY_SMI_ELEMENTS:
    140         return to_kind != FAST_SMI_ELEMENTS &&
    141             to_kind != FAST_HOLEY_SMI_ELEMENTS;
    142       case FAST_DOUBLE_ELEMENTS:
    143         return to_kind != FAST_SMI_ELEMENTS &&
    144             to_kind != FAST_HOLEY_SMI_ELEMENTS &&
    145             to_kind != FAST_DOUBLE_ELEMENTS;
    146       case FAST_HOLEY_DOUBLE_ELEMENTS:
    147         return to_kind == FAST_ELEMENTS ||
    148             to_kind == FAST_HOLEY_ELEMENTS;
    149       case FAST_ELEMENTS:
    150         return to_kind == FAST_HOLEY_ELEMENTS;
    151       case FAST_HOLEY_ELEMENTS:
    152         return false;
    153       default:
    154         return false;
    155     }
    156   }
    157   return false;
    158 }
    159 
    160 
    161 }  // namespace internal
    162 }  // namespace v8
    163