In the process of translating the GIMPLE into SSA, gcc first computed the dominance frontier of the CFG. I want to compute the control dependence graph from the dominance frontiers computed just now. The computed dominance frontier for all basic blocks is stored in the array of bitmap structure -"dfs", which means dfs[X] is the dominance frontier of basic block X. The process in the function "rewite_into_ssa()". However I don't understand clearly about what a certain bit in dfs[x] stands for.Without the clear notation of dfs, I can't change it to the CDG. Would someone tell me how the "dfs" represents dominance frontier , or another way to compute control dependence graph ? Thanks in advance~^_^