EricWF created this revision.
EricWF added reviewers: rsmith, mclow.lists.
See https://bugs.llvm.org/show_bug.cgi?id=20855
Libc++ goes out of it's way to diagnose `std::tuple` constructions which are UB
due to lifetime bugs caused by reference creation. For example:
// The 'const std::string&' is created *inside* the tuple constructor, and
its lifetime is over before the end of the constructor call.
std::tuple<int, const std::string&> t(std::make_tuple(42, "abc"));
However, we are over-aggressive and we incorrectly diagnose cases such as:
void foo(std::tuple<int const&, int const&> const&);
foo(std::make_tuple(42, 42));
This patch fixes the incorrectly diagnosed cases, as well as converting the
diagnostic to use the newly added Clang trait `__reference_binds_to_temporary`.
The new trait allows us to diagnose cases we previously couldn't such as:
std::tuple<int, const std::string&> t(42, "abc");
https://reviews.llvm.org/D41977
Files:
include/tuple
test/std/utilities/tuple/tuple.tuple/tuple.cnstr/PR20855_tuple_ref_binding_diagnostics.fail.cpp
test/std/utilities/tuple/tuple.tuple/tuple.cnstr/PR20855_tuple_ref_binding_diagnostics.pass.cpp
Index: test/std/utilities/tuple/tuple.tuple/tuple.cnstr/PR20855_tuple_ref_binding_diagnostics.pass.cpp
===================================================================
--- /dev/null
+++ test/std/utilities/tuple/tuple.tuple/tuple.cnstr/PR20855_tuple_ref_binding_diagnostics.pass.cpp
@@ -0,0 +1,47 @@
+// -*- C++ -*-
+//===----------------------------------------------------------------------===//
+//
+// The LLVM Compiler Infrastructure
+//
+// This file is dual licensed under the MIT and the University of Illinois Open
+// Source Licenses. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+
+// UNSUPPORTED: c++98, c++03
+
+// <tuple>
+
+// See llvm.org/PR20855
+
+#include <tuple>
+#include <string>
+#include "test_macros.h"
+
+#if TEST_HAS_BUILTIN_IDENTIFIER(__reference_binds_to_temporary)
+# define ASSERT_REFERENCE_BINDS_TEMPORARY(...) static_assert(__reference_binds_to_temporary(__VA_ARGS__), "")
+# define ASSERT_NOT_REFERENCE_BINDS_TEMPORARY(...) static_assert(!__reference_binds_to_temporary(__VA_ARGS__), "")
+#else
+# define ASSERT_REFERENCE_BINDS_TEMPORARY(...) static_assert(true, "")
+# define ASSERT_NOT_REFERENCE_BINDS_TEMPORARY(...) static_assert(true, "")
+#endif
+
+static_assert(std::is_same<decltype("abc"), decltype(("abc"))>::value, "");
+ASSERT_REFERENCE_BINDS_TEMPORARY(std::string const&, decltype("abc"));
+ASSERT_REFERENCE_BINDS_TEMPORARY(std::string const&, decltype(("abc")));
+ASSERT_REFERENCE_BINDS_TEMPORARY(std::string const&, const char*&&);
+
+template <class ...Args, class Tup = std::tuple<Args...>>
+void F(Tup const&) {}
+
+int main() {
+ {
+ F<int, int const&>(std::make_tuple<const int&, const int&>(42, 42));
+ std::tuple<int, int const&> t(std::make_tuple<const int&, const int&>(42, 42));
+ }
+ {
+ auto fn = &F<int, std::string const&>;
+ fn(std::tuple<int, std::string const&>(42, std::string("a")));
+ fn(std::make_tuple(42, std::string("a")));
+ }
+}
Index: test/std/utilities/tuple/tuple.tuple/tuple.cnstr/PR20855_tuple_ref_binding_diagnostics.fail.cpp
===================================================================
--- /dev/null
+++ test/std/utilities/tuple/tuple.tuple/tuple.cnstr/PR20855_tuple_ref_binding_diagnostics.fail.cpp
@@ -0,0 +1,54 @@
+// -*- C++ -*-
+//===----------------------------------------------------------------------===//
+//
+// The LLVM Compiler Infrastructure
+//
+// This file is dual licensed under the MIT and the University of Illinois Open
+// Source Licenses. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+
+// UNSUPPORTED: c++98, c++03
+
+// <tuple>
+
+// See llvm.org/PR20855
+
+#ifdef __clang__
+#pragma clang diagnostic ignored "-Wdangling-field"
+#endif
+
+#include <tuple>
+#include <string>
+#include "test_macros.h"
+
+
+#if !TEST_HAS_BUILTIN_IDENTIFIER(__reference_binds_to_temporary)
+#else
+# define ASSERT_REFERENCE_BINDS_TEMPORARY(...) static_assert(true, "")
+# define ASSERT_NOT_REFERENCE_BINDS_TEMPORARY(...) static_assert(true, "")
+#endif
+
+template <class T> struct CannotDeduce {
+ using type = T;
+};
+
+template <class ...Args>
+void F(typename CannotDeduce<std::tuple<Args...>>::type const&) {}
+
+
+int main() {
+ // expected-error@tuple:* 1 {{"Attempted to construct a reference element in a tuple with an rvalue"}}
+ {
+ F<int, const std::string&>(std::make_tuple(1, "abc")); // expected-note 1 {{requested here}}
+ }
+#if TEST_HAS_BUILTIN_IDENTIFIER(__reference_binds_to_temporary)
+ // expected-error@tuple:* 2 {{"Attempted to construct a reference element in a tuple with an rvalue"}}
+ {
+ std::tuple<int, const std::string&> t(1, "a"); // expected-note 1 {{requested here}}
+ }
+ {
+ F<int, const std::string&>(std::tuple<int, const std::string&>(1, "abc")); // expected-note 1 {{requested here}}
+ }
+#endif
+}
Index: include/tuple
===================================================================
--- include/tuple
+++ include/tuple
@@ -173,16 +173,24 @@
template <class _Tp>
static constexpr bool __can_bind_reference() {
+#if !__has_keyword(__reference_binds_to_temporary)
using _RawTp = typename remove_reference<_Tp>::type;
using _RawHp = typename remove_reference<_Hp>::type;
+
using _CheckLValueArg = integral_constant<bool,
is_lvalue_reference<_Tp>::value
|| is_same<_RawTp, reference_wrapper<_RawHp>>::value
|| is_same<_RawTp, reference_wrapper<typename remove_const<_RawHp>::type>>::value
+ // Allow "int&&" to bind to 'int const&'
+ || (is_rvalue_reference<_Tp>::value && is_const<_RawHp>::value &&
+ is_same<_RawHp, const _RawTp>::value)
>;
return !is_reference<_Hp>::value
|| (is_lvalue_reference<_Hp>::value && _CheckLValueArg::value)
|| (is_rvalue_reference<_Hp>::value && !is_lvalue_reference<_Tp>::value);
+#else
+ return !__reference_binds_to_temporary(_Hp, _Tp);
+#endif
}
__tuple_leaf& operator=(const __tuple_leaf&);
@@ -224,14 +232,14 @@
_LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX11
explicit __tuple_leaf(_Tp&& __t) _NOEXCEPT_((is_nothrow_constructible<_Hp, _Tp>::value))
: __value_(_VSTD::forward<_Tp>(__t))
- {static_assert(__can_bind_reference<_Tp>(),
+ {static_assert(__can_bind_reference<_Tp&&>(),
"Attempted to construct a reference element in a tuple with an rvalue");}
template <class _Tp, class _Alloc>
_LIBCPP_INLINE_VISIBILITY
explicit __tuple_leaf(integral_constant<int, 0>, const _Alloc&, _Tp&& __t)
: __value_(_VSTD::forward<_Tp>(__t))
- {static_assert(__can_bind_reference<_Tp>(),
+ {static_assert(__can_bind_reference<_Tp&&>(),
"Attempted to construct a reference element in a tuple with an rvalue");}
template <class _Tp, class _Alloc>
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