Previously, all operands to Constant were themselves constant.

Previously, all operands to Constant were themselves constant.
In the new world order, BlockAddress can have a BasicBlock operand.
This doesn't permute much, because if you have a ConstantExpr (or
anything more specific than Constant) we still know the operand has
to be a Constant.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@85375 91177308-0d34-0410-b5e6-96231b3b80d8