The original version of the code in XRayInstrumentation.cpp assumed that
functions may not have empty machine basic blocks (or that the first one
couldn't be). This change addresses that by special-casing that specific
situation.
We provide two .mir test-cases to make sure we're handling this
appropriately.
Fixes llvm.org/PR31424.
Reviewers: chandlerc
Subscribers: varno, llvm-commits
Differential Revision: https://reviews.llvm.org/D27913
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@290091 91177308-0d34-0410-b5e6-96231b3b80d8
Dean Michael Berris