Number SlotIndexes uniformly without looking at the number of defs on each instruction.

Number SlotIndexes uniformly without looking at the number of defs on each instruction.

You can't really predict how many indexes will be needed from the number of
defs, so let's keep it simple.

Also remove an extra empty index that was inserted after each basic block. It
was intended for live-out ranges, but it was never used that way.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@127014 91177308-0d34-0410-b5e6-96231b3b80d8