A MachineLoopRange contains the intervals of slot indexes covered by the blocks
in a loop. This representation of the loop blocks is more efficient to compare
against interfering registers during register coalescing.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@121917 91177308-0d34-0410-b5e6-96231b3b80d8
