On Thu, Sep 23, 2021 at 11:08:37AM -0700, Thomas Rodgers wrote:
> From: Thomas Rodgers <rodg...@twrodgers.com>
>
> This change implements P0528 which requires that padding bits not
> participate in atomic compare exchange operations. All arguments to the
Thanks for working on this.
> generic template are 'sanitized' by the __builtin_clear_padding intrinsic
> before they are used in atomic compare_exchange. This alrequires that any
> stores also sanitize the incoming value.
Not a review, just random nit.
Shouldn't the __builtin_clear_padding calls be guarded with
#if __has_builtin(__builtin_clear_padding)
or #ifdef _GLIBCXX_HAVE_BUILTIN_CLEAR_PADDING defined based on that?
I think clang doesn't support it (yet?), and it doesn't support the MSVC
__builtin_zero_non_value_bits (with very similar, but slightly different,
behavior).
> Signed-off-by: Thomas Rodgers <trodg...@redhat.com>
>
> libstdc++=v3/ChangeLog:
>
> * include/std/atomic (atomic<T>::atomic(_Tp) clear padding for
> __cplusplus > 201703L.
> (atomic<T>::store()) Clear padding.
> (atomic<T>::exchange()) Likewise.
> (atomic<T>::compare_exchange_weak()) Likewise.
> (atomic<T>::compare_exchange_strong()) Likewise.
> * testsuite/29_atomics/atomic/compare_exchange_padding.cc: New
> test.
Jakub
