The terminal barrier of a cmpxchg expansion will be either Acquire or
SequentiallyConsistent. In either case it can be skipped if the
operation has Monotonic requirements on failure.
rdar://problem/15996804
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@205535 91177308-0d34-0410-b5e6-96231b3b80d8
There's a barrier instruction so that should still be used, but most actual
atomic operations are going to need a platform decision on the correct
behaviour (either nop if single-threaded or OS-support otherwise).
rdar://problem/15287210
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@193399 91177308-0d34-0410-b5e6-96231b3b80d8
ARM processors without ldrex/strex need to be able to make libcalls for all
atomic operations, including the newer min/max versions.
The alternative would probably be expanding these operations in terms of
cmpxchg (as x86 does always), but in the configurations where this matters
code-size tends to be paramount so the libcall is more desirable.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@193398 91177308-0d34-0410-b5e6-96231b3b80d8
Thumb2 instructions are mostly constrained to rGPR, not tGPR which is
for Thumb1.
rdar://problem/12203728
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@162968 91177308-0d34-0410-b5e6-96231b3b80d8
