https://gcc.gnu.org/bugzilla/show_bug.cgi?id=80446
Bug ID: 80446
Summary: UNRESOLVED: 18_support/launder/1.cc compilation failed
to produce executable
Product: gcc
Version: 7.0.1
Status: UNCONFIRMED
Keywords: rejects-valid
Severity: normal
Priority: P3
Component: libstdc++
Assignee: unassigned at gcc dot gnu.org
Reporter: redi at gcc dot gnu.org
Target Milestone: ---
This test fails on FreeBSD and Cygwin, because their libc does:
#ifndef __has_builtin
#define __has_builtin(x) 0
#endif
This breaks our preprocessor checks for trying not to break older versions of
Clang which don't support the builtin:
#ifdef __has_builtin
# if !__has_builtin(__builtin_launder)
// Try not to break non-GNU compilers that don't support the built-in:
# define _GLIBCXX_NO_BUILTIN_LAUNDER 1
# endif
#endif
#ifndef _GLIBCXX_NO_BUILTIN_LAUNDER
namespace std
{
#define __cpp_lib_launder 201606
Because those libc headers define __has_builtin we determine that GCC doesn't
support the builtin.
The same problem exists for std::is_aggregate (but the test doesn't fail,
because it doesn't include a libc header before <type_traits>).
We'd have the same problem if users defined __has_builtin before including our
headers.
Maybe we should just remove the attempt to support older Clang releases, or do:
#if __GNUC__ >= 7
# define _GLIBCXX_HAVE_BUILTIN_LAUNDER 1
#elif defined __has_builtin
# if __has_builtin(__builtin_launder)
# define _GLIBCXX_HAVE_BUILTIN_LAUNDER 1
# endif
#endif
