This fixes a very subtle ABI problem concerning the copy constructor of
pair, and a couple of pair-like implementation detail types. The
C++98/03 and 11 standards all specify that the copy constructor of
pair<int, int> is trivial. However as libc++ tracked the draft C++11
standard over the years, this copy constructor became non-trivial, and
then just recently was corrected back to trivial for C++11.
Unfortunately (for libc++1) the Itanium ABI specifies different calling
conventions for trivial and non-trivial copy constructors. Therefore
currently the C++03 libc++ copy constructor for pair<int, int> is ABI
incompatible with the C++11 libc++ copy constructor for pair<int, int>.
This is Bad(tm). This patch corrects the situation by making this copy
constructor trivial in C++03 mode as well.
Just in case it is needed for an incomplete C++11 compiler, libc++
retains the ability to support pair with rvalue references, but without
defaulted special members. However the pair needs non-trivial special
members to implement this special case, (as it did when clang was in
this place a couple of years ago).
During this work a bug was also found and fixed in
is_trivially_constructible.
And there is a minor drive-by fix in <__config> regarding
__type_visibility__.
A test is updated to ensure that the copy constructor of pair<int, int>
is trivial in both C++03 and C++11. This test will necessarily fail for
a compiler that implements rvalue references but not defaulted special
members.
llvm-svn: 194536
diff --git a/libcxx/include/utility b/libcxx/include/utility
index 5fc2cf2..303dd4e 100644
--- a/libcxx/include/utility
+++ b/libcxx/include/utility
@@ -275,7 +275,7 @@
#ifndef _LIBCPP_HAS_NO_DEFAULTED_FUNCTIONS
_LIBCPP_INLINE_VISIBILITY
pair(const pair& __p) = default;
-#else
+#elif !defined(_LIBCPP_HAS_NO_RVALUE_REFERENCES) // default the copy ctor in C++03
_LIBCPP_INLINE_VISIBILITY
pair(const pair& __p)
_NOEXCEPT_(is_nothrow_copy_constructible<first_type>::value &&