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

[Jonathan Wakely]

On 21/02/19 20:47 +0000, Jonathan Wakely wrote:
>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.

That patch doesn't work with Clang because I made the members
protected and forgot to make them public again (and GCC doesn't cre,
only Clang notices).

Tested powerpc64le-linux, committed to trunk.



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