[LLVMdev] Find all backedges of CFG by MachineDominatorTree. please look at my jpg.
bboissin+llvm at gmail.com
Mon Jan 25 02:14:46 PST 2010
2010/1/25 任坤 <hbrenkun at yahoo.cn>:
> I hope to cut all backedges of MachineFunction CFG, then topological sort MachineBasicBlocks.
> 1. MachineDominatorTree *domintree = new MachineDominatorTree();
> 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.
> 3. how do I find all backedges of CFG???
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.
More information about the llvm-dev