[libcxx] Optimize vectors uninitialized construction of trivial types…

… from an iterator range.

Summary:
In certain cases vector can use memcpy to construct a range of elements at the back of the vector. We currently don't do this resulting in terrible code gen in non-optimized mode and a
very large slowdown compared to libstdc++. 

This patch adds a `__construct_forward_range(Allocator, Iter, Iter, _Ptr&)` and `__construct_forward_range(Allocator, Tp*, Tp*, Tp*&)` functions to `allocator_traits` which act similarly to the existing `__construct_forward(...)` functions.

This patch also changes vectors `__construct_at_end(Iter, Iter)` to be `__construct_at_end(Iter, Iter, SizeType)` where SizeType is the size of the range. `__construct_at_end(Iter, Iter, SizeType)` now calls `allocator_traits<Tp>::__construct_forward_range(...)`. 

This patch is based off the design of `__swap_out_circular_buffer(...)` which uses `allocator_traits<Tp>::__construct_forward(...)`.

On my machine this code performs 4x better than the current implementation when tested against `std::vector<int>`. 



Reviewers: howard.hinnant, titus, kcc, mclow.lists

Reviewed By: mclow.lists

Subscribers: cfe-commits

Differential Revision: http://reviews.llvm.org/D8109

llvm-svn: 233711

libcxx/include/memory

@@ -1525,6 +1525,34 @@ struct _LIBCPP_TYPE_VIS_ONLY allocator_traits
             __begin2 += _Np;
         }
 
+    template <class _Iter, class _Ptr>
+        _LIBCPP_INLINE_VISIBILITY
+        static
+        void
+        __construct_range_forward(allocator_type& __a, _Iter __begin1, _Iter __end1, _Ptr& __begin2)
+        {
+            for (; __begin1 != __end1; ++__begin1, (void) ++__begin2)
+                construct(__a, _VSTD::__to_raw_pointer(__begin2), *__begin1);
+        }
+
+    template <class _Tp>
+        _LIBCPP_INLINE_VISIBILITY
+        static
+        typename enable_if
+        <
+            (is_same<allocator_type, allocator<_Tp> >::value
+                || !__has_construct<allocator_type, _Tp*, _Tp>::value) &&
+             is_trivially_move_constructible<_Tp>::value,
+            void
+        >::type
+        __construct_range_forward(allocator_type& __a, _Tp* __begin1, _Tp* __end1, _Tp*& __begin2)
+        {
+            typedef typename remove_const<_Tp>::type _Vp;
+            ptrdiff_t _Np = __end1 - __begin1;
+            _VSTD::memcpy(const_cast<_Vp*>(__begin2), __begin1, _Np * sizeof(_Tp));
+            __begin2 += _Np;
+        }
+
     template <class _Ptr>
         _LIBCPP_INLINE_VISIBILITY
         static

libcxx/include/vector

@@ -783,7 +783,7 @@ private:
             __is_forward_iterator<_ForwardIterator>::value,
             void
         >::type
-        __construct_at_end(_ForwardIterator __first, _ForwardIterator __last);
+        __construct_at_end(_ForwardIterator __first, _ForwardIterator __last, size_type __n);
     void __append(size_type __n);
     void __append(size_type __n, const_reference __x);
     _LIBCPP_INLINE_VISIBILITY
@@ -1021,16 +1021,12 @@ typename enable_if
     __is_forward_iterator<_ForwardIterator>::value,
     void
 >::type
-vector<_Tp, _Allocator>::__construct_at_end(_ForwardIterator __first, _ForwardIterator __last)
+vector<_Tp, _Allocator>::__construct_at_end(_ForwardIterator __first, _ForwardIterator __last, size_type __n)
 {
     allocator_type& __a = this->__alloc();
-    for (; __first != __last; ++__first)
-    {
-        __RAII_IncreaseAnnotator __annotator(*this);
-        __alloc_traits::construct(__a, _VSTD::__to_raw_pointer(this->__end_), *__first);
-        __annotator.__done();
-        ++this->__end_;
-    }
+    __RAII_IncreaseAnnotator __annotator(*this, __n);
+    __alloc_traits::__construct_range_forward(__a, __first, __last, this->__end_);
+    __annotator.__done();
 }
 
 //  Default constructs __n objects starting at __end_
@@ -1177,7 +1173,7 @@ vector<_Tp, _Allocator>::vector(_ForwardIterator __first,
     if (__n > 0)
     {
         allocate(__n);
-        __construct_at_end(__first, __last);
+        __construct_at_end(__first, __last, __n);
     }
 }
 
@@ -1197,7 +1193,7 @@ vector<_Tp, _Allocator>::vector(_ForwardIterator __first, _ForwardIterator __las
     if (__n > 0)
     {
         allocate(__n);
-        __construct_at_end(__first, __last);
+        __construct_at_end(__first, __last, __n);
     }
 }
 
@@ -1212,7 +1208,7 @@ vector<_Tp, _Allocator>::vector(const vector& __x)
     if (__n > 0)
     {
         allocate(__n);
-        __construct_at_end(__x.__begin_, __x.__end_);
+        __construct_at_end(__x.__begin_, __x.__end_, __n);
     }
 }
 
@@ -1227,7 +1223,7 @@ vector<_Tp, _Allocator>::vector(const vector& __x, const allocator_type& __a)
     if (__n > 0)
     {
         allocate(__n);
-        __construct_at_end(__x.__begin_, __x.__end_);
+        __construct_at_end(__x.__begin_, __x.__end_, __n);
     }
 }
 
@@ -1286,7 +1282,7 @@ vector<_Tp, _Allocator>::vector(initializer_list<value_type> __il)
     if (__il.size() > 0)
     {
         allocate(__il.size());
-        __construct_at_end(__il.begin(), __il.end());
+        __construct_at_end(__il.begin(), __il.end(), __il.size());
     }
 }
 
@@ -1301,7 +1297,7 @@ vector<_Tp, _Allocator>::vector(initializer_list<value_type> __il, const allocat
     if (__il.size() > 0)
     {
         allocate(__il.size());
-        __construct_at_end(__il.begin(), __il.end());
+        __construct_at_end(__il.begin(), __il.end(), __il.size());
     }
 }
 
@@ -1394,28 +1390,28 @@ typename enable_if
 >::type
 vector<_Tp, _Allocator>::assign(_ForwardIterator __first, _ForwardIterator __last)
 {
-    typename iterator_traits<_ForwardIterator>::difference_type __new_size = _VSTD::distance(__first, __last);
-    if (static_cast<size_type>(__new_size) <= capacity())
+    size_type __new_size = static_cast<size_type>(_VSTD::distance(__first, __last));
+    if (__new_size <= capacity())
     {
         _ForwardIterator __mid = __last;
         bool __growing = false;
-        if (static_cast<size_type>(__new_size) > size())
+        if (__new_size > size())
         {
             __growing = true;
             __mid =  __first;
             _VSTD::advance(__mid, size());
         }
         pointer __m = _VSTD::copy(__first, __mid, this->__begin_);
         if (__growing)
-            __construct_at_end(__mid, __last);
+            __construct_at_end(__mid, __last, __new_size - size());
         else
             this->__destruct_at_end(__m);
     }
     else
     {
         deallocate();
-        allocate(__recommend(static_cast<size_type>(__new_size)));
-        __construct_at_end(__first, __last);
+        allocate(__recommend(__new_size));
+        __construct_at_end(__first, __last, __new_size);
     }
 }
 
@@ -1967,8 +1963,9 @@ vector<_Tp, _Allocator>::insert(const_iterator __position, _ForwardIterator __fi
             if (__n > __dx)
             {
                 __m = __first;
-                _VSTD::advance(__m, this->__end_ - __p);
-                __construct_at_end(__m, __last);
+                difference_type __diff = this->__end_ - __p;
+                _VSTD::advance(__m, __diff);
+                __construct_at_end(__m, __last, __n - __diff);
                 __n = __dx;
             }
             if (__n > 0)