PR libstdc++/88840 delay evaluation of constant until type is complete

Clang fails to compile std::vector<Incomplete> because the static member
__use_relocate cannot be evaluated for an incomplete type. Replace with
a static member function that will not be odr-used until needed, by
which point the type must be complete.

	PR libstdc++/88840
	* include/bits/stl_vector.h (vector::__use_relocate): Replace static
	data member with static member function _S_use_relocate().
	* include/bits/vector.tcc (vector::reserve, vector::_M_realloc_insert)
	(vector::_M_default_append): Use _S_use_relocate() instead of
	__use_relocate.

From-SVN: r268239

libstdc++-v3/ChangeLog

 2019-01-24  Jonathan Wakely  <jwakely@redhat.com>
 
+	PR libstdc++/88840
+	* include/bits/stl_vector.h (vector::__use_relocate): Replace static
+	data member with static member function _S_use_relocate().
+	* include/bits/vector.tcc (vector::reserve, vector::_M_realloc_insert)
+	(vector::_M_default_append): Use _S_use_relocate() instead of
+	__use_relocate.
+
 	* testsuite/27_io/filesystem/path/compare/strings.cc: Only compare
 	sign of results.
 

libstdc++-v3/include/bits/stl_vector.h

@@ -424,11 +424,14 @@ _GLIBCXX_BEGIN_NAMESPACE_CONTAINER
 
     private:
 #if __cplusplus >= 201103L
-      static constexpr bool __use_relocate =
-	noexcept(std::__relocate_a(std::declval<pointer>(),
-				   std::declval<pointer>(),
-				   std::declval<pointer>(),
-				   std::declval<_Tp_alloc_type&>()));
+      static constexpr bool
+      _S_use_relocate()
+      {
+	return noexcept(std::__relocate_a(std::declval<pointer>(),
+					  std::declval<pointer>(),
+					  std::declval<pointer>(),
+					  std::declval<_Tp_alloc_type&>()));
+      }
 #endif
 
     protected:

libstdc++-v3/include/bits/vector.tcc

@@ -73,7 +73,7 @@ _GLIBCXX_BEGIN_NAMESPACE_CONTAINER
 	  const size_type __old_size = size();
 	  pointer __tmp;
 #if __cplusplus >= 201103L
-	  if constexpr (__use_relocate)
+	  if constexpr (_S_use_relocate())
 	    {
 	      __tmp = this->_M_allocate(__n);
 	      std::__relocate_a(this->_M_impl._M_start,
@@ -457,7 +457,7 @@ _GLIBCXX_BEGIN_NAMESPACE_CONTAINER
 	  __new_finish = pointer();
 
 #if __cplusplus >= 201103L
-	  if constexpr (__use_relocate)
+	  if constexpr (_S_use_relocate())
 	    {
 	      __new_finish
 		= std::__relocate_a
@@ -498,7 +498,7 @@ _GLIBCXX_BEGIN_NAMESPACE_CONTAINER
 	  __throw_exception_again;
 	}
 #if __cplusplus >= 201103L
-      if constexpr (!__use_relocate)
+      if constexpr (!_S_use_relocate())
 #endif
 	std::_Destroy(__old_start, __old_finish, _M_get_Tp_allocator());
       _GLIBCXX_ASAN_ANNOTATE_REINIT;
@@ -639,7 +639,7 @@ _GLIBCXX_BEGIN_NAMESPACE_CONTAINER
 		_M_check_len(__n, "vector::_M_default_append");
 	      pointer __new_start(this->_M_allocate(__len));
 #if __cplusplus >= 201103L
-	      if constexpr (__use_relocate)
+	      if constexpr (_S_use_relocate())
 		{
 		  __try
 		    {