I was raising two questions:
1)ependence loop in SelectionDAG.
there is no loop in a DAG,but i did meet a situation there was a loop.
an example is a BR node targets a node after it in the chain.
to the BR node . the target node is an operand .
to the target node, the BR node is in the "Chain" pointed to by operand 0.
is it wro
in some nodes, operand 0 is a Chain.