Summary:
Comparing against the empty string should generate much better code that
what it does today.
We can also generate better code when comparing against literals that
are larger than the SSO space.
Reviewers: EricWF
Subscribers: christof, jdoerfert, libcxx-commits
Tags: #libc
Differential Revision: https://reviews.llvm.org/D59781
llvm-svn: 357614