Clang 3.9 regression causes a bug when generating code for
std::atomic_compare_and_exchange*(std::atomic<long long>,...) without
optimizations. If same code is compiled with -O2 tests pass without problems.
Atomics are implement in headers with builtin functions which makes this
affect application code instead of libc++ library code.
libcxx tests default to -O0 compilation so these test need to be marked failing
on arm to allow installing packages. Use cases is so borderline failure that it
shouldn't prevent building the package. (64bit atomics in 32bit mode)
Gbp-Pq: Topic libcxx
Gbp-Pq: Name libcxx-test-atomics-set-compare-exchange-to-be-expected-fails-on-arm.patch
Lock is_always_lock free test fails on i386 because std::atomic is aligned
Lock is_always_lock free test fails on i386 because std::atomic is aligned
to 8 bytes while long long is aligned to 4 bytes. clang can't generate inline
code for unaligned 8 byte atomics even tough instruction set and gcc support
it.
That makes it expected thaqt ATOMIC_LLONG_LOCK_FREE and
std::atomic<long long>::is_always_lock_free don't match on i386. Correct test
for std::atomic<long long> is to check if target cpu support cmpxchg8 instruction.
To set instruction support one can check __GCC_HAVE_SYNC_COMPARE_AND_SWAP_8 define.
Bug: https://llvm.org/bugs/show_bug.cgi?id=19355
Gbp-Pq: Topic libcxx
Gbp-Pq: Name libcxx-test-fix-lockfree-test-for-i386.patch
LLVM Packaging Team