using ARMeilleure.IntermediateRepresentation; using System.Diagnostics; namespace ARMeilleure.Translation { static class Dominance { // Those methods are an implementation of the algorithms on "A Simple, Fast Dominance Algorithm". // https://www.cs.rice.edu/~keith/EMBED/dom.pdf public static void FindDominators(ControlFlowGraph cfg) { BasicBlock Intersect(BasicBlock block1, BasicBlock block2) { while (block1 != block2) { while (cfg.PostOrderMap[block1.Index] < cfg.PostOrderMap[block2.Index]) { block1 = block1.ImmediateDominator; } while (cfg.PostOrderMap[block2.Index] < cfg.PostOrderMap[block1.Index]) { block2 = block2.ImmediateDominator; } } return block1; } cfg.Entry.ImmediateDominator = cfg.Entry; Debug.Assert(cfg.Entry == cfg.PostOrderBlocks[cfg.PostOrderBlocks.Length - 1]); bool modified; do { modified = false; for (int blkIndex = cfg.PostOrderBlocks.Length - 2; blkIndex >= 0; blkIndex--) { BasicBlock block = cfg.PostOrderBlocks[blkIndex]; BasicBlock newIDom = null; foreach (BasicBlock predecessor in block.Predecessors) { if (predecessor.ImmediateDominator != null) { if (newIDom != null) { newIDom = Intersect(predecessor, newIDom); } else { newIDom = predecessor; } } } if (block.ImmediateDominator != newIDom) { block.ImmediateDominator = newIDom; modified = true; } } } while (modified); } public static void FindDominanceFrontiers(ControlFlowGraph cfg) { foreach (BasicBlock block in cfg.Blocks) { if (block.Predecessors.Count < 2) { continue; } for (int pBlkIndex = 0; pBlkIndex < block.Predecessors.Count; pBlkIndex++) { BasicBlock current = block.Predecessors[pBlkIndex]; while (current != block.ImmediateDominator) { current.DominanceFrontiers.Add(block); current = current.ImmediateDominator; } } } } } }