Author: dim
Date: Wed Aug 19 01:43:33 2015
New Revision: 245421
URL: http://llvm.org/viewvc/llvm-project?rev=245421&view=rev
Log:
Fix warnings about pessimizing return moves for C++11 and higher
Summary:
Throughout the libc++ headers, there are a few instances where
_VSTD::move() is used to return a local variable. Howard commented in
r189039 that these were there "for non-obvious reasons such as to help
things limp along in C++03 language mode".
However, when compiling these headers with warnings on, and in C++11 or
higher mode (like we do in FreeBSD), they cause the following complaints
about pessimizing moves:
In file included from tests.cpp:26:
In file included from tests.hpp:29:
/usr/include/c++/v1/map:1368:12: error: moving a local object in a return
statement prevents copy elision [-Werror,-Wpessimizing-move]
return _VSTD::move(__h); // explicitly moved for C++03
^
/usr/include/c++/v1/__config:368:15: note: expanded from macro '_VSTD'
#define _VSTD std::_LIBCPP_NAMESPACE
^
Attempt to fix this by adding a _LIBCPP_EXPLICIT_MOVE() macro to
__config, which gets defined to _VSTD::move for pre-C++11, and to
nothing for C++11 and later.
I am not completely satisfied with the macro name (I also considered
_LIBCPP_COMPAT_MOVE and some other variants), so suggestions are
welcome. :)
Reviewers: mclow.lists, howard.hinnant, EricWF
Subscribers: arthur.j.odwyer, cfe-commits
Differential Revision: http://reviews.llvm.org/D11394
Modified:
libcxx/trunk/include/__config
libcxx/trunk/include/__hash_table
libcxx/trunk/include/__tree
libcxx/trunk/include/algorithm
libcxx/trunk/include/ext/hash_map
libcxx/trunk/include/map
libcxx/trunk/include/unordered_map
Modified: libcxx/trunk/include/__config
URL:
http://llvm.org/viewvc/llvm-project/libcxx/trunk/include/__config?rev=245421&r1=245420&r2=245421&view=diff
==============================================================================
--- libcxx/trunk/include/__config (original)
+++ libcxx/trunk/include/__config Wed Aug 19 01:43:33 2015
@@ -716,6 +716,12 @@ template <unsigned> struct __static_asse
#define _LIBCPP_CONSTEXPR_AFTER_CXX11
#endif
+#ifdef _LIBCPP_HAS_NO_RVALUE_REFERENCES
+# define _LIBCPP_EXPLICIT_MOVE(x) _VSTD::move(x)
+#else
+# define _LIBCPP_EXPLICIT_MOVE(x) (x)
+#endif
+
#ifndef _LIBCPP_HAS_NO_ASAN
extern "C" void __sanitizer_annotate_contiguous_container(
const void *, const void *, const void *, const void *);
Modified: libcxx/trunk/include/__hash_table
URL:
http://llvm.org/viewvc/llvm-project/libcxx/trunk/include/__hash_table?rev=245421&r1=245420&r2=245421&view=diff
==============================================================================
--- libcxx/trunk/include/__hash_table (original)
+++ libcxx/trunk/include/__hash_table Wed Aug 19 01:43:33 2015
@@ -2108,7 +2108,7 @@ __hash_table<_Tp, _Hash, _Equal, _Alloc>
__h.get_deleter().__value_constructed = true;
__h->__hash_ = hash_function()(__h->__value_);
__h->__next_ = nullptr;
- return _VSTD::move(__h); // explicitly moved for C++03
+ return _LIBCPP_EXPLICIT_MOVE(__h); // explicitly moved for C++03
}
#endif // _LIBCPP_HAS_NO_RVALUE_REFERENCES
@@ -2124,7 +2124,7 @@ __hash_table<_Tp, _Hash, _Equal, _Alloc>
__h.get_deleter().__value_constructed = true;
__h->__hash_ = __hash;
__h->__next_ = nullptr;
- return _VSTD::move(__h); // explicitly moved for C++03
+ return _LIBCPP_EXPLICIT_MOVE(__h); // explicitly moved for C++03
}
template <class _Tp, class _Hash, class _Equal, class _Alloc>
Modified: libcxx/trunk/include/__tree
URL:
http://llvm.org/viewvc/llvm-project/libcxx/trunk/include/__tree?rev=245421&r1=245420&r2=245421&view=diff
==============================================================================
--- libcxx/trunk/include/__tree (original)
+++ libcxx/trunk/include/__tree Wed Aug 19 01:43:33 2015
@@ -1843,7 +1843,7 @@ __tree<_Tp, _Compare, _Allocator>::__con
__node_holder __h(__node_traits::allocate(__na, 1), _Dp(__na));
__node_traits::construct(__na, _VSTD::addressof(__h->__value_), __v);
__h.get_deleter().__value_constructed = true;
- return _VSTD::move(__h); // explicitly moved for C++03
+ return _LIBCPP_EXPLICIT_MOVE(__h); // explicitly moved for C++03
}
#endif // _LIBCPP_HAS_NO_RVALUE_REFERENCES
Modified: libcxx/trunk/include/algorithm
URL:
http://llvm.org/viewvc/llvm-project/libcxx/trunk/include/algorithm?rev=245421&r1=245420&r2=245421&view=diff
==============================================================================
--- libcxx/trunk/include/algorithm (original)
+++ libcxx/trunk/include/algorithm Wed Aug 19 01:43:33 2015
@@ -851,7 +851,7 @@ for_each(_InputIterator __first, _InputI
{
for (; __first != __last; ++__first)
__f(*__first);
- return _VSTD::move(__f); // explicitly moved for (emulated) C++03
+ return _LIBCPP_EXPLICIT_MOVE(__f); // explicitly moved for (emulated)
C++03
}
// find
Modified: libcxx/trunk/include/ext/hash_map
URL:
http://llvm.org/viewvc/llvm-project/libcxx/trunk/include/ext/hash_map?rev=245421&r1=245420&r2=245421&view=diff
==============================================================================
--- libcxx/trunk/include/ext/hash_map (original)
+++ libcxx/trunk/include/ext/hash_map Wed Aug 19 01:43:33 2015
@@ -681,7 +681,7 @@ hash_map<_Key, _Tp, _Hash, _Pred, _Alloc
__h.get_deleter().__first_constructed = true;
__node_traits::construct(__na, _VSTD::addressof(__h->__value_.second));
__h.get_deleter().__second_constructed = true;
- return _VSTD::move(__h); // explicitly moved for C++03
+ return _LIBCPP_EXPLICIT_MOVE(__h); // explicitly moved for C++03
}
template <class _Key, class _Tp, class _Hash, class _Pred, class _Alloc>
Modified: libcxx/trunk/include/map
URL:
http://llvm.org/viewvc/llvm-project/libcxx/trunk/include/map?rev=245421&r1=245420&r2=245421&view=diff
==============================================================================
--- libcxx/trunk/include/map (original)
+++ libcxx/trunk/include/map Wed Aug 19 01:43:33 2015
@@ -1523,7 +1523,7 @@ map<_Key, _Tp, _Compare, _Allocator>::__
__h.get_deleter().__first_constructed = true;
__node_traits::construct(__na,
_VSTD::addressof(__h->__value_.__cc.second));
__h.get_deleter().__second_constructed = true;
- return _VSTD::move(__h); // explicitly moved for C++03
+ return _LIBCPP_EXPLICIT_MOVE(__h); // explicitly moved for C++03
}
template <class _Key, class _Tp, class _Compare, class _Allocator>
Modified: libcxx/trunk/include/unordered_map
URL:
http://llvm.org/viewvc/llvm-project/libcxx/trunk/include/unordered_map?rev=245421&r1=245420&r2=245421&view=diff
==============================================================================
--- libcxx/trunk/include/unordered_map (original)
+++ libcxx/trunk/include/unordered_map Wed Aug 19 01:43:33 2015
@@ -1511,7 +1511,7 @@ unordered_map<_Key, _Tp, _Hash, _Pred, _
__h.get_deleter().__first_constructed = true;
__node_traits::construct(__na,
_VSTD::addressof(__h->__value_.__cc.second));
__h.get_deleter().__second_constructed = true;
- return _VSTD::move(__h); // explicitly moved for C++03
+ return _LIBCPP_EXPLICIT_MOVE(__h); // explicitly moved for C++03
}
template <class _Key, class _Tp, class _Hash, class _Pred, class _Alloc>
_______________________________________________
cfe-commits mailing list
cfe-commits@lists.llvm.org
http://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-commits
