[PATCH] D48342: [libcxx] Optimize vectors construction of trivial types from an iterator range with const-ness mismatch.

[Volodymyr Sapsai via Phabricator via cfe-commits]

vsapsai updated this revision to Diff 180316.
vsapsai added a comment.

- Tweak the test.
- Use for `__construct_range_forward` approach recommended by @ldionne (it works with C++03).
- Use `__is_default_allocator` for `__construct_forward` and `__construct_backward`.

Didn't introduce `remove_const` to `__construct_forward` and
`__construct_backward` because they don't allow mixing types.


CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D48342/new/

https://reviews.llvm.org/D48342

Files:
  libcxx/include/memory
  libcxx/test/std/containers/sequences/vector/vector.cons/construct_iter_iter.pass.cpp


Index: libcxx/test/std/containers/sequences/vector/vector.cons/construct_iter_iter.pass.cpp
===================================================================
--- libcxx/test/std/containers/sequences/vector/vector.cons/construct_iter_iter.pass.cpp
+++ libcxx/test/std/containers/sequences/vector/vector.cons/construct_iter_iter.pass.cpp
@@ -146,9 +146,20 @@
 #endif
 }
 
+// Initialize a vector with a different value type. Make sure initialization
+// is performed with each element value, not with a memory blob.
+void test_ctor_with_different_value_type() {
+  float array[3] = {0.0f, 1.0f, 2.0f};
+  std::vector<int> v(array, array + 3);
+  assert(v[0] == 0);
+  assert(v[1] == 1);
+  assert(v[2] == 2);
+}
+
 
 int main() {
   basic_test_cases();
   emplaceable_concept_tests(); // See PR34898
   test_ctor_under_alloc();
+  test_ctor_with_different_value_type();
 }
Index: libcxx/include/memory
===================================================================
--- libcxx/include/memory
+++ libcxx/include/memory
@@ -1502,6 +1502,12 @@
     typedef typename _Alloc::difference_type type;
 };
 
+template <class _Tp>
+struct __is_default_allocator : false_type {};
+
+template <class _Tp>
+struct __is_default_allocator<_VSTD::allocator<_Tp> > : true_type {};
+
 template <class _Alloc>
 struct _LIBCPP_TEMPLATE_VIS allocator_traits
 {
@@ -1615,7 +1621,7 @@
         static
         typename enable_if
         <
-            (is_same<allocator_type, allocator<_Tp> >::value
+            (__is_default_allocator<allocator_type>::value
                 || !__has_construct<allocator_type, _Tp*, _Tp>::value) &&
              is_trivially_move_constructible<_Tp>::value,
             void
@@ -1640,23 +1646,25 @@
                 construct(__a, _VSTD::__to_raw_pointer(__begin2), *__begin1);
         }
 
-    template <class _Tp>
+    template <class _SourceTp, class _DestTp,
+              class _RawSourceTp = typename remove_const<_SourceTp>::type,
+              class _RawDestTp = typename remove_const<_DestTp>::type>
         _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,
+            is_trivially_move_constructible<_DestTp>::value &&
+            is_same<_RawSourceTp, _RawDestTp>::value &&
+            (__is_default_allocator<allocator_type>::value ||
+             !__has_construct<allocator_type, _DestTp*, _SourceTp&>::value),
             void
         >::type
-        __construct_range_forward(allocator_type&, _Tp* __begin1, _Tp* __end1, _Tp*& __begin2)
+        __construct_range_forward(allocator_type&, _SourceTp* __begin1, _SourceTp* __end1, _DestTp*& __begin2)
         {
-            typedef typename remove_const<_Tp>::type _Vp;
             ptrdiff_t _Np = __end1 - __begin1;
             if (_Np > 0)
             {
-                _VSTD::memcpy(const_cast<_Vp*>(__begin2), __begin1, _Np * sizeof(_Tp));
+                _VSTD::memcpy(const_cast<_RawDestTp*>(__begin2), __begin1, _Np * sizeof(_DestTp));
                 __begin2 += _Np;
             }
         }
@@ -1679,7 +1687,7 @@
         static
         typename enable_if
         <
-            (is_same<allocator_type, allocator<_Tp> >::value
+            (__is_default_allocator<allocator_type>::value
                 || !__has_construct<allocator_type, _Tp*, _Tp>::value) &&
              is_trivially_move_constructible<_Tp>::value,
             void


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