I hope to cut all backedges of MachineFunction CFG, then topological sort MachineBasicBlocks.
1. MachineDominatorTree *domintree = new MachineDominatorTree();
domintree->runOnMachineFunction(mf);
2. Then travel mf one by one.
When domintree->dominates(next,current) is true, there is a backedge from current node to next node. move this backedge form CFG.
But I find A LOOP in some CFG, there is backedge from current to next, dominates function reture "FALSE". So my algorithm find Graph can not be
toplogical sort.
For non-reducible graphs (as is the case for your example), it is no
longer true that the target of a back-edge dominates the source.
If you want back-edges, just do a depth-first search of the CFG, the
back-edges are the edges going to an already processed node. If you
want loop-edges (edges going to loop headers, that is more generic
than back-edges), you'll need to build the loop nesting forest.
