libstdc++: Implement P1328 "Making std::type_info::operator== constexpr"
Commit Message
Not committed yet ...
This feature is present in the C++23 draft. The ARM EABI requires that
the type_info::operator== function can be defined out-of-line (and
suggests that should be the default). With this patch, we fail to
conform to that in C++23 mode. I think we might want to move the logic
from operator== into a separate std::type_info::__equal function, which
can be non-inline even if the actual type_info::operator== function is
constexpr (and so implicitly inline). That isn't done by this patch, but
probably should be.
libstdc++-v3/ChangeLog:
* include/bits/c++config (_GLIBCXX23_CONSTEXPR): Define.
* include/std/version (__cpp_lib_constexpr_typeinfo): Define.
* libsupc++/tinfo.cc: Add #error to ensure non-inline definition
is emitted.
* libsupc++/typeinfo (type_info::name()): Avoid branching.
(type_info::before): Combine different implementations into one.
(type_info::operator==): Likewise.
---
libstdc++-v3/include/bits/c++config | 10 +++-
libstdc++-v3/include/std/version | 1 +
libstdc++-v3/libsupc++/tinfo.cc | 4 ++
libstdc++-v3/libsupc++/typeinfo | 90 ++++++++++++++++++-----------
4 files changed, 70 insertions(+), 35 deletions(-)
@@ -175,13 +175,21 @@
#endif
#ifndef _GLIBCXX20_CONSTEXPR
-# if __cplusplus > 201703L
+# if __cplusplus >= 202002L
# define _GLIBCXX20_CONSTEXPR constexpr
# else
# define _GLIBCXX20_CONSTEXPR
# endif
#endif
+#ifndef _GLIBCXX23_CONSTEXPR
+# if __cplusplus >= 202100L
+# define _GLIBCXX23_CONSTEXPR constexpr
+# else
+# define _GLIBCXX23_CONSTEXPR
+# endif
+#endif
+
#ifndef _GLIBCXX17_INLINE
# if __cplusplus >= 201703L
# define _GLIBCXX17_INLINE inline
@@ -290,6 +290,7 @@
#if __cplusplus > 202002L
// c++2b
#define __cpp_lib_adaptor_iterator_pair_constructor 202106L
+#define __cpp_lib_constexpr_typeinfo 202106L
#define __cpp_lib_invoke_r 202106L
#define __cpp_lib_is_scoped_enum 202011L
#if __cpp_lib_concepts
@@ -32,6 +32,10 @@ std::type_info::
#if !__GXX_TYPEINFO_EQUALITY_INLINE
+#if __cplusplus > 202002L
+# error "this file must be compiled with C++20 or older to define operator=="
+#endif
+
// We can't rely on common symbols being shared between shared objects.
bool std::type_info::
operator== (const std::type_info& arg) const _GLIBCXX_NOEXCEPT
@@ -38,6 +38,10 @@
#pragma GCC visibility push(default)
+#if __cplusplus >= 202101L
+# define __cpp_lib_constexpr_typeinfo 202106L
+#endif
+
extern "C++" {
namespace __cxxabiv1
@@ -97,42 +101,14 @@ namespace std
/** Returns an @e implementation-defined byte string; this is not
* portable between compilers! */
const char* name() const _GLIBCXX_NOEXCEPT
- { return __name[0] == '*' ? __name + 1 : __name; }
+ { return __name + int(__name[0] == '*'); }
-#if !__GXX_TYPEINFO_EQUALITY_INLINE
- // In old abi, or when weak symbols are not supported, there can
- // be multiple instances of a type_info object for one
- // type. Uniqueness must use the _name value, not object address.
- bool before(const type_info& __arg) const _GLIBCXX_NOEXCEPT;
- bool operator==(const type_info& __arg) const _GLIBCXX_NOEXCEPT;
-#else
- #if !__GXX_MERGED_TYPEINFO_NAMES
- /** Returns true if @c *this precedes @c __arg in the implementation's
+ /** Returns true if `*this` precedes `__arg` in the implementation's
* collation order. */
- // Even with the new abi, on systems that support dlopen
- // we can run into cases where type_info names aren't merged,
- // so we still need to do string comparison.
- bool before(const type_info& __arg) const _GLIBCXX_NOEXCEPT
- { return (__name[0] == '*' && __arg.__name[0] == '*')
- ? __name < __arg.__name
- : __builtin_strcmp (__name, __arg.__name) < 0; }
+ bool before(const type_info& __arg) const _GLIBCXX_NOEXCEPT;
- bool operator==(const type_info& __arg) const _GLIBCXX_NOEXCEPT
- {
- return ((__name == __arg.__name)
- || (__name[0] != '*' &&
- __builtin_strcmp (__name, __arg.__name) == 0));
- }
- #else
- // On some targets we can rely on type_info's NTBS being unique,
- // and therefore address comparisons are sufficient.
- bool before(const type_info& __arg) const _GLIBCXX_NOEXCEPT
- { return __name < __arg.__name; }
-
- bool operator==(const type_info& __arg) const _GLIBCXX_NOEXCEPT
- { return __name == __arg.__name; }
- #endif
-#endif
+ _GLIBCXX23_CONSTEXPR
+ bool operator==(const type_info& __arg) const _GLIBCXX_NOEXCEPT;
#if __cpp_impl_three_way_comparison < 201907L
bool operator!=(const type_info& __arg) const _GLIBCXX_NOEXCEPT
@@ -176,11 +152,57 @@ namespace std
explicit type_info(const char *__n): __name(__n) { }
private:
- /// Assigning type_info is not supported.
+ // type_info objects cannot be copied.
+#if __cplusplus >= 201103L
+ type_info& operator=(const type_info&) = delete;
+ type_info(const type_info&) = delete;
+#else
type_info& operator=(const type_info&);
type_info(const type_info&);
+#endif
};
+#if __GXX_TYPEINFO_EQUALITY_INLINE
+ inline bool
+ type_info::before(const type_info& __arg) const _GLIBCXX_NOEXCEPT
+ {
+#if !__GXX_MERGED_TYPEINFO_NAMES
+ // Even with the new abi, on systems that support dlopen
+ // we can run into cases where type_info names aren't merged,
+ // so we still need to do string comparison.
+ if (__name[0] != '*' || __arg.__name[0] != '*')
+ return __builtin_strcmp (__name, __arg.__name) < 0;
+#else
+ // On some targets we can rely on type_info's NTBS being unique,
+ // and therefore address comparisons are sufficient.
+#endif
+
+ // In old abi, or when weak symbols are not supported, there can
+ // be multiple instances of a type_info object for one
+ // type. Uniqueness must use the __name value, not object address.
+ return __name < __arg.__name;
+ }
+#endif
+
+#if __GXX_TYPEINFO_EQUALITY_INLINE || __cplusplus > 202002L
+ _GLIBCXX23_CONSTEXPR inline bool
+ type_info::operator==(const type_info& __arg) const _GLIBCXX_NOEXCEPT
+ {
+ if (__name == __arg.__name)
+ return true;
+
+#if !__GXX_MERGED_TYPEINFO_NAMES
+# if __has_builtin(__builtin_is_constant_evaluated)
+ if (!__builtin_is_constant_evaluated())
+# endif
+ return __name[0] != '*' && __builtin_strcmp (__name, __arg.name()) == 0;
+#endif
+
+ return false;
+ }
+# endif
+
+
/**
* @brief Thrown during incorrect typecasting.
* @ingroup exceptions