AtomicExpandPass uses this variable to determine emitting libcalls or not. The default value is 1024 and if we don't specify it for PPC64 explicitly, AtomicExpandPass won't emit `__atomic_*` libcalls for those target unable to inline atomic ops and finally the backend emits `__sync_*` libcalls. Thanks @efriedma for pointing it out.
Reviewed By: efriedma
Differential Revision: https://reviews.llvm.org/D122868
When generating a all-one mask value whose bitwidth is larger than 64, signed extension should be used rather then zero extension.
Reviewed By: jsji
Differential Revision: https://reviews.llvm.org/D120865
Kai Luo