Re: [PATCH 8/8] libstdc++: Do not define lock-free atomic aliases if not fully lock-free [PR114103]

[Jonathan Wakely <jwakely@redhat.com>]

On Tue, 27 Feb 2024 at 11:49, Jonathan Wakely <jwakely@redhat.com> wrote:
>
> Tested x86_64-linux. I think we should make this change, because
> otherwise we define the typedefs for platforms with no lock-free
> atomics, like hppa-hpux. Instead of lying, those typedefs should be
> absent on that target.
>
> -- >8 --
>
> libstdc++-v3/ChangeLog:
>
>         PR libstdc++/114103
>         * include/bits/version.def (atomic_lock_free_type_aliases): Add
>         extra_cond to check for at least one always-lock-free type.
>         * include/bits/version.h: Regenerate.
>         * include/std/atomic (atomic_signed_lock_free)
>         (atomic_unsigned_lock_free): Only use always-lock-free types.
> ---
>  libstdc++-v3/include/bits/version.def | 1 +
>  libstdc++-v3/include/bits/version.h   | 2 +-
>  libstdc++-v3/include/std/atomic       | 6 +++---
>  3 files changed, 5 insertions(+), 4 deletions(-)
>
> diff --git a/libstdc++-v3/include/bits/version.def b/libstdc++-v3/include/bits/version.def
> index 502961eb269..d298420121b 100644
> --- a/libstdc++-v3/include/bits/version.def
> +++ b/libstdc++-v3/include/bits/version.def
> @@ -739,6 +739,7 @@ ftms = {
>    values = {
>      v = 201907;
>      cxxmin = 20;
> +    extra_cond = "(__GCC_ATOMIC_INT_LOCK_FREE | __GCC_ATOMIC_LONG_LOCK_FREE | __GCC_ATOMIC_CHAR_LOCK_FREE) & 2";

Maybe this should be > 1 instead of & 2 in case there are targets that
define it to 4 or something. I think those are only supposed to be
defined to 0, 1, or 2 though.


>    };
>  };
>
> diff --git a/libstdc++-v3/include/bits/version.h b/libstdc++-v3/include/bits/version.h
> index 7a6fbd35e2e..9107b45a484 100644
> --- a/libstdc++-v3/include/bits/version.h
> +++ b/libstdc++-v3/include/bits/version.h
> @@ -819,7 +819,7 @@
>  #undef __glibcxx_want_atomic_float
>
>  #if !defined(__cpp_lib_atomic_lock_free_type_aliases)
> -# if (__cplusplus >= 202002L)
> +# if (__cplusplus >= 202002L) && ((__GCC_ATOMIC_INT_LOCK_FREE | __GCC_ATOMIC_LONG_LOCK_FREE | __GCC_ATOMIC_CHAR_LOCK_FREE) & 2)
>  #  define __glibcxx_atomic_lock_free_type_aliases 201907L
>  #  if defined(__glibcxx_want_all) || defined(__glibcxx_want_atomic_lock_free_type_aliases)
>  #   define __cpp_lib_atomic_lock_free_type_aliases 201907L
> diff --git a/libstdc++-v3/include/std/atomic b/libstdc++-v3/include/std/atomic
> index 559f8370459..1462cf5ec23 100644
> --- a/libstdc++-v3/include/std/atomic
> +++ b/libstdc++-v3/include/std/atomic
> @@ -1774,13 +1774,13 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>      = atomic<make_signed_t<__detail::__platform_wait_t>>;
>    using atomic_unsigned_lock_free
>      = atomic<make_unsigned_t<__detail::__platform_wait_t>>;
> -# elif ATOMIC_INT_LOCK_FREE || !(ATOMIC_LONG_LOCK_FREE || ATOMIC_CHAR_LOCK_FREE)
> +# elif ATOMIC_INT_LOCK_FREE == 2

Similarly, this could be > 1 but again, I think == 2 is OK.

>    using atomic_signed_lock_free = atomic<signed int>;
>    using atomic_unsigned_lock_free = atomic<unsigned int>;
> -# elif ATOMIC_LONG_LOCK_FREE
> +# elif ATOMIC_LONG_LOCK_FREE == 2
>    using atomic_signed_lock_free = atomic<signed long>;
>    using atomic_unsigned_lock_free = atomic<unsigned long>;
> -# elif ATOMIC_CHAR_LOCK_FREE
> +# elif ATOMIC_CHAR_LOCK_FREE == 2
>    using atomic_signed_lock_free = atomic<signed char>;
>    using atomic_unsigned_lock_free = atomic<unsigned char>;
>  # else
> --
> 2.43.0
>