mi-sched: Don't call MBB.size() in initSUnits. The driver already has instr count.

This fixes a pathological compile time problem with very large blocks
and lots of scheduling boundaries.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@189116 91177308-0d34-0410-b5e6-96231b3b80d8
6 files changed