Add an implementation of C11's stdatomic.h

Description

Add an implementation of C11's stdatomic.h

Adds a Clang-specific implementation of C11's stdatomic.h header. On systems,
such as FreeBSD, where a stdatomic.h header is already provided, we defer to
that header instead (using our has_include_next technology). Otherwise, we
provide an implementation in terms of our
c11_atomic_* intrinsics (that were
created for this purpose).

C11 7.1.4p1 requires function declarations for atomic_thread_fence,
atomic_signal_fence, atomic_flag_test_and_set,
atomic_flag_test_and_set_explicit, and atomic_flag_clear, and requires that
they have external linkage. Accordingly, we provide these declarations, but if
a user elides the shadowing macros and uses them, then they must have a libc
(or similar) that actually provides definitions.

atomic_flag is implemented using _Bool as the underlying type. This is
consistent with the implementation provided by FreeBSD and also GCC 4.9 (at
least when __GCC_ATOMIC_TEST_AND_SET_TRUEVAL == 1).

Patch by Richard Smith (rebased and slightly edited by me -- Richard said I
should drive at this point).

Details

Committed
hfinkelOct 2 2014, 9:29 PM
Parents
rL218956: [x86] Add another triple to a test to make the comment syntax stable.
Branches
Unknown
Tags
Unknown