Propagate branch metadata when some branch probability is missing.

Summary: In sample profile, some branches may have profile missing due to profile inaccuracy. We want existing branch probability still valid after propagation.

Reviewers: hfinkel, davidxl, spatel

Subscribers: llvm-commits

Differential Revision: http://reviews.llvm.org/D19948

llvm-svn: 269137
2 files changed