[SimplifyCFG] Fix for non-determinism in codegen

Summary: This patch fixes issues in codegen uncovered due to https://reviews.llvm.org/D26718

Reviewers: majnemer, chenli, davide

Reviewed By: davide

Subscribers: davide, arsenm, llvm-commits

Differential Revision: https://reviews.llvm.org/D26726

llvm-svn: 301222