aco/util: add small_vec

Signed-off-by: Rhys Perry <pendingchaos02@gmail.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/27984>

src/amd/compiler/aco_util.h

@@ -1031,6 +1031,153 @@ using bitfield_array64 = bitfield_array<T, offset, size, uint64_t>;
 
 using bitarray8 = bitfield_array<uint8_t, 0, 8, uint8_t>;
 
+/*
+ * Resizable array optimized for small lengths. If it's smaller than Size, the elements will be
+ * inlined into the object.
+ */
+template <typename T, uint32_t Size> class small_vec {
+public:
+   static_assert(std::is_trivially_copyable<T>::value);
+   static_assert(std::is_trivially_destructible<T>::value);
+
+   using value_type = T;
+   using pointer = value_type*;
+   using const_pointer = const value_type*;
+   using reference = value_type&;
+   using const_reference = const value_type&;
+   using iterator = pointer;
+   using const_iterator = const_pointer;
+   using reverse_iterator = std::reverse_iterator<iterator>;
+   using const_reverse_iterator = std::reverse_iterator<const_iterator>;
+   using size_type = uint16_t;
+   using difference_type = std::ptrdiff_t;
+
+   constexpr small_vec() = default;
+   constexpr small_vec(const small_vec&) = delete;
+
+   ~small_vec()
+   {
+      if (capacity > Size)
+         free(data);
+   }
+
+   constexpr small_vec& operator=(const small_vec&) = delete;
+
+   constexpr iterator begin() noexcept { return capacity > Size ? data : inline_data; }
+
+   constexpr const_iterator begin() const noexcept { return capacity > Size ? data : inline_data; }
+
+   constexpr iterator end() noexcept { return std::next(begin(), length); }
+
+   constexpr const_iterator end() const noexcept { return std::next(begin(), length); }
+
+   constexpr const_iterator cbegin() const noexcept { return begin(); }
+
+   constexpr const_iterator cend() const noexcept { return std::next(begin(), length); }
+
+   constexpr reverse_iterator rbegin() noexcept { return reverse_iterator(end()); }
+
+   constexpr const_reverse_iterator rbegin() const noexcept
+   {
+      return const_reverse_iterator(end());
+   }
+
+   constexpr reverse_iterator rend() noexcept { return reverse_iterator(begin()); }
+
+   constexpr const_reverse_iterator rend() const noexcept
+   {
+      return const_reverse_iterator(begin());
+   }
+
+   constexpr const_reverse_iterator crbegin() const noexcept
+   {
+      return const_reverse_iterator(cend());
+   }
+
+   constexpr const_reverse_iterator crend() const noexcept
+   {
+      return const_reverse_iterator(cbegin());
+   }
+
+   constexpr reference operator[](const size_type index) noexcept
+   {
+      assert(length > index);
+      return *(std::next(begin(), index));
+   }
+
+   constexpr const_reference operator[](const size_type index) const noexcept
+   {
+      assert(length > index);
+      return *(std::next(begin(), index));
+   }
+
+   constexpr reference back() noexcept
+   {
+      assert(length > 0);
+      return *(std::next(begin(), length - 1));
+   }
+
+   constexpr const_reference back() const noexcept
+   {
+      assert(length > 0);
+      return *(std::next(begin(), length - 1));
+   }
+
+   constexpr reference front() noexcept
+   {
+      assert(length > 0);
+      return *begin();
+   }
+
+   constexpr const_reference front() const noexcept
+   {
+      assert(length > 0);
+      return *cbegin();
+   }
+
+   constexpr bool empty() const noexcept { return length == 0; }
+
+   constexpr size_type size() const noexcept { return length; }
+
+   constexpr void pop_back() noexcept
+   {
+      assert(length > 0);
+      --length;
+   }
+
+   template <typename... Args> constexpr void emplace_back(Args... args) noexcept
+   {
+      if (length == capacity) {
+         if (capacity > Size) {
+            capacity *= 2;
+            data = (T*)realloc(data, sizeof(T) * capacity);
+         } else {
+            capacity *= 2;
+            T* ptr = (T*)malloc(sizeof(T) * capacity);
+            memcpy(ptr, inline_data, sizeof(T) * length);
+            data = ptr;
+         }
+      }
+      *std::next(begin(), length++) = T(args...);
+   }
+
+   constexpr void clear() noexcept
+   {
+      if (capacity > Size)
+         free(data);
+      length = 0;
+      capacity = 0;
+   }
+
+private:
+   uint32_t length = 0;
+   uint32_t capacity = Size;
+   union {
+      T* data = NULL;
+      T inline_data[Size];
+   };
+};
+
 } // namespace aco
 
 #endif // ACO_UTIL_H