Assert that input blocks meet the invariants we expect

Simplify the input/output finder.  All elements of a basic block are
instructions.  Any used arguments are also inputs.  An instruction can only
be used by another instruction.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@12405 91177308-0d34-0410-b5e6-96231b3b80d8
1 file changed