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From: "richard-gccbugzilla at metafoo dot co.uk" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug c/64843] miscompilation of atomic_fetch_add on atomic pointer type
Date: Wed, 28 Jan 2015 21:44:00 -0000	[thread overview]
Message-ID: <bug-64843-4-iJEnr2cREe@http.gcc.gnu.org/bugzilla/> (raw)
In-Reply-To: <bug-64843-4@http.gcc.gnu.org/bugzilla/>

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=64843

--- Comment #2 from Richard Smith <richard-gccbugzilla at metafoo dot co.uk> ---
libstdc++ uses these builtins in bits/atomic_base.h:

      __pointer_type
      fetch_add(ptrdiff_t __d,
                memory_order __m = memory_order_seq_cst) noexcept
      { return __atomic_fetch_add(&_M_p, _M_type_size(__d), __m); }

Naturally, it's up to you guys how you handle this, but it would be problematic
at least for Clang if the semantics of __atomic_fetch_add change to match the
documentation: we'd somehow need to detect which flavor of libstdc++ is in use
when compiling <atomic>. There may also be user code that depends on the
current semantics that would be broken by changing the de facto semantics (that
have been present for many GCC releases).


Here's Clang's documentation for its __c11_* builtin set:

  http://clang.llvm.org/docs/LanguageExtensions.html#c11-atomic-builtins


  parent reply	other threads:[~2015-01-28 21:44 UTC|newest]

Thread overview: 7+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2015-01-28 19:38 [Bug c/64843] New: " richard-gccbugzilla at metafoo dot co.uk
2015-01-28 20:38 ` [Bug c/64843] " rguenth at gcc dot gnu.org
2015-01-28 21:44 ` richard-gccbugzilla at metafoo dot co.uk [this message]
2015-01-28 23:20 ` joseph at codesourcery dot com
2015-01-28 23:24 ` joseph at codesourcery dot com
2015-01-29  0:05 ` richard-gccbugzilla at metafoo dot co.uk
2015-01-29  1:04 ` redi at gcc dot gnu.org

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