Tested on x86_64-pc-linux-gnu, does this look OK for trunk?
-- >8 --
When checking __is_complete_or_unbounded on a reference to incomplete
type, we overeagerly try to instantiate/complete the referenced type
which besides being unnecessary may also produce a -Wsfinae-incomplete
warning (added in r16-1527) if the referenced type is later defined.
This patch fixes this by effectively restricting the sizeof check to
object (except unknown-bound array) types. In passing simplify the
implementation by using is_object instead of is_function/reference/void.
PR libstdc++/120717
libstdc++-v3/ChangeLog:
* include/std/type_traits (__is_complete_or_unbounded): Don't
check sizeof on a reference or unbounded array type. Simplify
using is_object. Correct formatting.
* testsuite/20_util/is_complete_or_unbounded/120717.cc: New test.
---
libstdc++-v3/include/std/type_traits | 34 +++++++++----------
.../is_complete_or_unbounded/120717.cc | 20 +++++++++++
2 files changed, 37 insertions(+), 17 deletions(-)
create mode 100644
libstdc++-v3/testsuite/20_util/is_complete_or_unbounded/120717.cc
diff --git a/libstdc++-v3/include/std/type_traits
b/libstdc++-v3/include/std/type_traits
index abff9f880001..28960befd2c7 100644
--- a/libstdc++-v3/include/std/type_traits
+++ b/libstdc++-v3/include/std/type_traits
@@ -280,11 +280,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
// Forward declarations
template<typename>
- struct is_reference;
- template<typename>
- struct is_function;
- template<typename>
- struct is_void;
+ struct is_object;
template<typename>
struct remove_cv;
template<typename>
@@ -297,18 +293,22 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
// Helper functions that return false_type for incomplete classes,
// incomplete unions and arrays of known bound from those.
- template <typename _Tp, size_t = sizeof(_Tp)>
- constexpr true_type __is_complete_or_unbounded(__type_identity<_Tp>)
- { return {}; }
-
- template <typename _TypeIdentity,
- typename _NestedType = typename _TypeIdentity::type>
- constexpr typename __or_<
- is_reference<_NestedType>,
- is_function<_NestedType>,
- is_void<_NestedType>,
- __is_array_unknown_bounds<_NestedType>
- >::type __is_complete_or_unbounded(_TypeIdentity)
+ // More specialized overload for complete object types.
+ template<typename _Tp,
+ typename = __enable_if_t<!__or_<__not_<is_object<_Tp>>,
+
__is_array_unknown_bounds<_Tp>>::value>,
+ size_t = sizeof(_Tp)>
+ constexpr true_type
+ __is_complete_or_unbounded(__type_identity<_Tp>)
+ { return {}; };
+
+ // Less specialized overload for reference and unknown-bound array types, and
+ // incomplete types.
+ template<typename _TypeIdentity,
+ typename _NestedType = typename _TypeIdentity::type>
+ constexpr typename __or_<__not_<is_object<_NestedType>>,
+ __is_array_unknown_bounds<_NestedType>>::type
+ __is_complete_or_unbounded(_TypeIdentity)
{ return {}; }
// __remove_cv_t (std::remove_cv_t for C++11).
diff --git a/libstdc++-v3/testsuite/20_util/is_complete_or_unbounded/120717.cc
b/libstdc++-v3/testsuite/20_util/is_complete_or_unbounded/120717.cc
new file mode 100644
index 000000000000..31fdf8fe9227
--- /dev/null
+++ b/libstdc++-v3/testsuite/20_util/is_complete_or_unbounded/120717.cc
@@ -0,0 +1,20 @@
+// PR libstdc++/120717
+// { dg-do compile { target c++11 } }
+// { dg-additional-options "-Wsfinae-incomplete" }
+
+#include <type_traits>
+
+// Verify __is_complete_or_unbounded doesn't try to instantiate the underlying
+// type of a reference or array of unknown bound.
+template<class T> struct A { static_assert(false, "do not instantiate"); };
+static_assert(std::__is_complete_or_unbounded(std::__type_identity<A<int>&>{}),
"");
+static_assert(std::__is_complete_or_unbounded(std::__type_identity<A<int>&&>{}),
"");
+static_assert(std::__is_complete_or_unbounded(std::__type_identity<A<int>[]>{}),
"");
+
+// Verify __is_complete_or_unbounded doesn't produce -Wsfinae-incomplete
+// warnings.
+struct B;
+static_assert(std::__is_complete_or_unbounded(std::__type_identity<B&>{}), "");
+static_assert(std::__is_complete_or_unbounded(std::__type_identity<B&&>{}),
"");
+static_assert(std::__is_complete_or_unbounded(std::__type_identity<B[]>{}),
"");
+struct B { }; // { dg-bogus "-Wsfinae-incomplete" }
--
2.50.0.81.gcb3b40381e
