[libc++] Add a key function for bad_function_call

Summary:
bad_function_call is currently an empty class, so any object files using
that class will end up with their own copy of its typeinfo, typeinfo
name and vtable, leading to unnecessary duplication that has to be
resolved by the dynamic linker. Instead, give bad_function_call a key
function and put a definition for that key function in libc++ itself, to
centralize the typeinfo and vtable.

This is consistent with the behavior for other exception classes. The
key functions are defined in libc++ rather than libc++abi since the
class is defined in the libc++ versioning namespace, so ABI
compatibility with libstdc++ is not a concern.

Guard this change behind an ABI macro, since it isn't backwards
compatible (i.e., clients built against the new libc++ headers wouldn't
be able to run against an older libc++ library).

Reviewers: mclow.lists, EricWF

Subscribers: mgorny, cfe-commits

Differential Revision: https://reviews.llvm.org/D27387

llvm-svn: 298937

1 files changed, 6 insertions, 0 deletions

diff --git a/libcxx/include/functional b/libcxx/include/functional
index 977ada67f33..fecac4e41f8 100644
--- a/libcxx/include/functional
+++ b/libcxx/include/functional
@@ -1389,6 +1389,12 @@ mem_fn(_Rp _Tp::* __pm) _NOEXCEPT
 class _LIBCPP_EXCEPTION_ABI bad_function_call
     : public exception
 {
+#ifdef _LIBCPP_ABI_BAD_FUNCTION_CALL_KEY_FUNCTION
+public:
+    virtual ~bad_function_call() _NOEXCEPT;
+
+    virtual const char* what() const _NOEXCEPT;
+#endif
 };
 
 _LIBCPP_NORETURN inline _LIBCPP_ALWAYS_INLINE