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

[Jonathan Wakely]

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.

Tested powerpc64le-linux, committed to trunk.



commit 423d29c6e0a9e6b17901f1b04ac31060aa91c17a
Author: Jonathan Wakely <jwak...@redhat.com>
Date:   Thu Jan 24 14:58:36 2019 +0000

    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.

diff --git a/libstdc++-v3/include/bits/stl_vector.h 
b/libstdc++-v3/include/bits/stl_vector.h
index 54de0e09ce7..43debda54f1 100644
--- a/libstdc++-v3/include/bits/stl_vector.h
+++ b/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:
diff --git a/libstdc++-v3/include/bits/vector.tcc 
b/libstdc++-v3/include/bits/vector.tcc
index edd0b6aeaa8..4cf0e809fe9 100644
--- a/libstdc++-v3/include/bits/vector.tcc
+++ b/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
                    {