swift234

CSE: Calls that participate in cse need to be readnone

Currently this should not matter because isSideEffectFree calls isReadNone for
swift builtins. The only difference between isReadNone and isSideEffectFree is
that isSideEffectFree allows llvm intrinsics that are readonly.
Looking at llvm's intrinsic td file I did not see any readonly functions so we
should also be safe before this change. But better safe than sorry - especially
if someone changes the implementation of isSideEffectFree to be more permissable
later.

Swift SVN r21239