Line data    Source code

       1             : // Copyright 2018 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_BASE_SMALL_VECTOR_H_
       6             : #define V8_BASE_SMALL_VECTOR_H_
       7             : 
       8             : #include <type_traits>
       9             : 
      10             : #include "src/base/bits.h"
      11             : #include "src/base/macros.h"
      12             : 
      13             : namespace v8 {
      14             : namespace base {
      15             : 
      16             : // Minimal SmallVector implementation. Uses inline storage first, switches to
      17             : // malloc when it overflows.
      18             : template <typename T, size_t kSize>
      19             : class SmallVector {
      20             :   // Currently only support trivially copyable and trivially destructible data
      21             :   // types, as it uses memcpy to copy elements and never calls destructors.
      22             :   ASSERT_TRIVIALLY_COPYABLE(T);
      23             :   STATIC_ASSERT(std::is_trivially_destructible<T>::value);
      24             : 
      25             :  public:
      26             :   static constexpr size_t kInlineSize = kSize;
      27             : 
      28     3267292 :   SmallVector() = default;
      29             :   SmallVector(const SmallVector& other) V8_NOEXCEPT { *this = other; }
      30      303472 :   SmallVector(SmallVector&& other) V8_NOEXCEPT { *this = std::move(other); }
      31             : 
      32             :   ~SmallVector() {
      33     2029842 :     if (is_big()) free(begin_);
      34     2029842 :   }
      35             : 
      36      129549 :   SmallVector& operator=(const SmallVector& other) V8_NOEXCEPT {
      37      129549 :     if (this == &other) return *this;
      38             :     size_t other_size = other.size();
      39      129552 :     if (capacity() < other_size) {
      40             :       // Create large-enough heap-allocated storage.
      41          32 :       if (is_big()) free(begin_);
      42          32 :       begin_ = reinterpret_cast<T*>(malloc(sizeof(T) * other_size));
      43          32 :       end_of_storage_ = begin_ + other_size;
      44             :     }
      45      129552 :     memcpy(begin_, other.begin_, sizeof(T) * other_size);
      46      129552 :     end_ = begin_ + other_size;
      47      129552 :     return *this;
      48             :   }
      49             : 
      50      151721 :   SmallVector& operator=(SmallVector&& other) V8_NOEXCEPT {
      51      151721 :     if (this == &other) return *this;
      52      151726 :     if (other.is_big()) {
      53           0 :       if (is_big()) free(begin_);
      54           0 :       begin_ = other.begin_;
      55           0 :       end_ = other.end_;
      56           0 :       end_of_storage_ = other.end_of_storage_;
      57             :       other.reset();
      58             :     } else {
      59             :       DCHECK_GE(capacity(), other.size());  // Sanity check.
      60             :       size_t other_size = other.size();
      61      151726 :       memcpy(begin_, other.begin_, sizeof(T) * other_size);
      62      151726 :       end_ = begin_ + other_size;
      63             :     }
      64             :     return *this;
      65             :   }
      66             : 
      67             :   T* data() { return begin_; }
      68             :   const T* data() const { return begin_; }
      69             : 
      70             :   T* begin() { return begin_; }
      71             :   const T* begin() const { return begin_; }
      72             : 
      73             :   T* end() { return end_; }
      74             :   const T* end() const { return end_; }
      75             : 
      76     2372910 :   size_t size() const { return end_ - begin_; }
      77             :   bool empty() const { return end_ == begin_; }
      78      482381 :   size_t capacity() const { return end_of_storage_ - begin_; }
      79             : 
      80             :   T& back() {
      81             :     DCHECK_NE(0, size());
      82      459853 :     return end_[-1];
      83             :   }
      84             : 
      85             :   T& operator[](size_t index) {
      86             :     DCHECK_GT(size(), index);
      87     6016133 :     return begin_[index];
      88             :   }
      89             : 
      90             :   const T& operator[](size_t index) const {
      91             :     DCHECK_GT(size(), index);
      92       62804 :     return begin_[index];
      93             :   }
      94             : 
      95             :   template <typename... Args>
      96     3311137 :   void emplace_back(Args&&... args) {
      97     3311137 :     if (V8_UNLIKELY(end_ == end_of_storage_)) Grow();
      98     3311363 :     new (end_) T(std::forward<Args>(args)...);
      99     3311363 :     ++end_;
     100     3311363 :   }
     101             : 
     102             :   void pop_back(size_t count = 1) {
     103             :     DCHECK_GE(size(), count);
     104     2392382 :     end_ -= count;
     105             :   }
     106             : 
     107      122289 :   void resize_no_init(size_t new_size) {
     108             :     // Resizing without initialization is safe if T is trivially copyable.
     109             :     ASSERT_TRIVIALLY_COPYABLE(T);
     110      336057 :     if (new_size > capacity()) Grow(new_size);
     111      336057 :     end_ = begin_ + new_size;
     112      122289 :   }
     113             : 
     114             :   // Clear without freeing any storage.
     115             :   void clear() { end_ = begin_; }
     116             : 
     117             :   // Clear and go back to inline storage.
     118             :   void reset() {
     119           0 :     begin_ = inline_storage_begin();
     120           0 :     end_ = begin_;
     121           0 :     end_of_storage_ = begin_ + kInlineSize;
     122             :   }
     123             : 
     124             :  private:
     125             :   T* begin_ = inline_storage_begin();
     126             :   T* end_ = begin_;
     127     1539903 :   T* end_of_storage_ = begin_ + kInlineSize;
     128             :   typename std::aligned_storage<sizeof(T) * kInlineSize, alignof(T)>::type
     129             :       inline_storage_;
     130             : 
     131       16772 :   void Grow(size_t min_capacity = 0) {
     132       16772 :     size_t in_use = end_ - begin_;
     133             :     size_t new_capacity =
     134       50316 :         base::bits::RoundUpToPowerOfTwo(std::max(min_capacity, 2 * capacity()));
     135       16772 :     T* new_storage = reinterpret_cast<T*>(malloc(sizeof(T) * new_capacity));
     136       16772 :     memcpy(new_storage, begin_, sizeof(T) * in_use);
     137       16772 :     if (is_big()) free(begin_);
     138       16772 :     begin_ = new_storage;
     139       16772 :     end_ = new_storage + in_use;
     140       16772 :     end_of_storage_ = new_storage + new_capacity;
     141       16772 :   }
     142             : 
     143     2181568 :   bool is_big() const { return begin_ != inline_storage_begin(); }
     144             : 
     145     1539903 :   T* inline_storage_begin() { return reinterpret_cast<T*>(&inline_storage_); }
     146             :   const T* inline_storage_begin() const {
     147     1653969 :     return reinterpret_cast<const T*>(&inline_storage_);
     148             :   }
     149             : };
     150             : 
     151             : }  // namespace base
     152             : }  // namespace v8
     153             : 
     154             : #endif  // V8_BASE_SMALL_VECTOR_H_