[libcxx] Properly convert the count arguments to the *_n algorithms before use.

Summary:
The requirement on the `Size` type passed to *_n algorithms is that it is convertible to an integral type. This means we can't use a variable of type `Size` directly. Instead we need to convert it to an integral type first.  The problem is finding out what integral type to convert it to.  `__convert_to_integral` figures out what integral type to convert it to and performs the conversion, It also promotes the resulting integral type so that it is at least as big as an integer. `__convert_to_integral` also has a special case for converting enums. This should only work on non-scoped enumerations because it does not apply an explicit conversion from the enum to its underlying type.



Reviewers: chandlerc, mclow.lists

Reviewed By: mclow.lists

Subscribers: cfe-commits

Differential Revision: http://reviews.llvm.org/D7449

git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@228704 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/include/algorithm b/include/algorithm
index 68173f4..475ba66 100644
--- a/include/algorithm
+++ b/include/algorithm
@@ -1672,7 +1672,8 @@
          _Size __count, const _Tp& __value_, _BinaryPredicate __pred)
 {
     return _VSTD::__search_n<typename add_lvalue_reference<_BinaryPredicate>::type>
-           (__first, __last, __count, __value_, __pred, typename iterator_traits<_ForwardIterator>::iterator_category());
+           (__first, __last, __convert_to_integral(__count), __value_, __pred,
+           typename iterator_traits<_ForwardIterator>::iterator_category());
 }
 
 template <class _ForwardIterator, class _Size, class _Tp>
@@ -1681,7 +1682,8 @@
 search_n(_ForwardIterator __first, _ForwardIterator __last, _Size __count, const _Tp& __value_)
 {
     typedef typename iterator_traits<_ForwardIterator>::value_type __v;
-    return _VSTD::search_n(__first, __last, __count, __value_, __equal_to<__v, _Tp>());
+    return _VSTD::search_n(__first, __last, __convert_to_integral(__count),
+                           __value_, __equal_to<__v, _Tp>());
 }
 
 // copy
@@ -1839,8 +1841,10 @@
    !__is_random_access_iterator<_InputIterator>::value,
     _OutputIterator
 >::type
-copy_n(_InputIterator __first, _Size __n, _OutputIterator __result)
+copy_n(_InputIterator __first, _Size __orig_n, _OutputIterator __result)
 {
+    typedef decltype(__convert_to_integral(__orig_n)) _IntegralSize;
+    _IntegralSize __n = __orig_n;
     if (__n > 0)
     {
         *__result = *__first;
@@ -1862,8 +1866,10 @@
     __is_random_access_iterator<_InputIterator>::value,
     _OutputIterator
 >::type
-copy_n(_InputIterator __first, _Size __n, _OutputIterator __result)
+copy_n(_InputIterator __first, _Size __orig_n, _OutputIterator __result)
 {
+    typedef decltype(__convert_to_integral(__orig_n)) _IntegralSize;
+    _IntegralSize __n = __orig_n;
     return _VSTD::copy(__first, __first + __n, __result);
 }
 
@@ -2055,7 +2061,7 @@
 _OutputIterator
 fill_n(_OutputIterator __first, _Size __n, const _Tp& __value_)
 {
-   return _VSTD::__fill_n(__first, __n, __value_);
+   return _VSTD::__fill_n(__first, __convert_to_integral(__n), __value_);
 }
 
 // fill
@@ -2101,8 +2107,10 @@
 template <class _OutputIterator, class _Size, class _Generator>
 inline _LIBCPP_INLINE_VISIBILITY
 _OutputIterator
-generate_n(_OutputIterator __first, _Size __n, _Generator __gen)
+generate_n(_OutputIterator __first, _Size __orig_n, _Generator __gen)
 {
+    typedef decltype(__convert_to_integral(__orig_n)) _IntegralSize;
+    _IntegralSize __n = __orig_n;
     for (; __n > 0; ++__first, (void) --__n)
         *__first = __gen();
     return __first;