[PATCH] libstdc++/89130 and libstdc++/89090 fixes for vector relocation

[Jonathan Wakely]

On 05/02/19 14:45 +0000, Jonathan Wakely wrote:
>This fixes two PRs, one trivial (don't use C++17 features in C++11
>mode) and one more serious (don't require MoveInsertable when we
>should only need CopyInsertable).
>
>It would be nice to rely on if-constexpr in C++11 mode, but it causes
>clang warnings, complicates testcase bisection/reduction, and causes
>users to file bogus bug reports. So let's just avoid it.
>
>Tested powerpc64le-linux, committed to trunk.
>
>

>commit 51908e56bd32b5f89bc909193c3da957de01c3e0
>Author: Jonathan Wakely <jwakely@redhat.com>
>Date:   Tue Feb 5 11:50:18 2019 +0000
>
>    PR libstdc++/89130 restore support for non-MoveConstructible types
>    
>    The changes to "relocate" std::vector elements can lead to new errors
>    outside the immediate context, because moving the elements to new
>    storage no longer makes use of the move-if-noexcept utilities. This
>    means that types with deleted moves no longer degenerate to copies, but
>    are just ill-formed. The errors happen while instantiating the
>    noexcept-specifier for __relocate_object_a, when deciding whether to try
>    to relocate.
>    
>    This patch introduces indirections to avoid the ill-formed
>    instantiations of std::__relocate_object_a. In order to avoid using
>    if-constexpr prior to C++17 this is done by tag dispatching. After this
>    patch all uses of std::__relocate_a are guarded by checks that will
>    support sensible code (i.e. code not using custom allocators that fool
>    the new checks).
>    
>            PR libstdc++/89130
>            * include/bits/alloc_traits.h (__is_copy_insertable_impl): Rename to
>            __is_alloc_insertable_impl. Replace single type member with two
>            members, one for each of copy and move insertable.
>            (__is_move_insertable): New trait for internal use.
>            * include/bits/stl_vector.h (vector::_S_nothrow_relocate(true_type))
>            (vector::_S_nothrow_relocate(true_type)): New functions to
>            conditionally check if __relocate_a can throw.
>            (vector::_S_use_relocate()): Dispatch to _S_nothrow_relocate based
>            on __is_move_insertable.
>            (vector::_S_do_relocate): New overloaded functions to conditionally
>            call __relocate_a.
>            (vector::_S_relocate): New function that dispatches to _S_do_relocate
>            based on _S_use_relocate.
>            * include/bits/vector.tcc (vector::reserve, vector::_M_realloc_insert)
>            (vector::_M_default_append): Call _S_relocate instead of __relocate_a.
>            * testsuite/23_containers/vector/modifiers/push_back/89130.cc: New.
>
>diff --git a/libstdc++-v3/include/bits/alloc_traits.h b/libstdc++-v3/include/bits/alloc_traits.h
>index ed61ce845f8..3b0c16fbf64 100644
>--- a/libstdc++-v3/include/bits/alloc_traits.h
>+++ b/libstdc++-v3/include/bits/alloc_traits.h
>@@ -577,14 +577,16 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>     }
> 
>   template<typename _Alloc>
>-    class __is_copy_insertable_impl
>+    class __is_alloc_insertable_impl
>     {
>-      typedef allocator_traits<_Alloc> _Traits;
>+      using _Traits = allocator_traits<_Alloc>;
>+      using value_type = typename _Traits::value_type;
> 
>-      template<typename _Up, typename
>+      template<typename _Up, typename _Tp = __remove_cvref_t<_Up>,
>+	       typename
> 	       = decltype(_Traits::construct(std::declval<_Alloc&>(),
>-					     std::declval<_Up*>(),
>-					     std::declval<const _Up&>()))>
>+					     std::declval<_Tp*>(),
>+					     std::declval<_Up>()))>
> 	static true_type
> 	_M_select(int);
> 
>@@ -593,13 +595,14 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
> 	_M_select(...);
> 
>     public:
>-      typedef decltype(_M_select<typename _Alloc::value_type>(0)) type;
>+      using copy = decltype(_M_select<const value_type&>(0));
>+      using move = decltype(_M_select<value_type>(0));

This caused another regression, fixed by the attached patch.

Tested powerpc64le-linux, committed to trunk.

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