We present a new linear-time algorithm to find the immediate dominators of all vertices in a flowgraph. Our algorithm is simpler than previous linear-time algorithms: rather than employ complicated data structures, we combine the use of microtrees and memoization with new observations on a restricted class of path compressions. We have implemented our algorithm, and we report experimental results that show that the constant factors are low. Compared to the standard, slightly superlinear

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... m of Lengauer and Tarjan, which has much less overhead, our algorithm runs 10-20% slower on real flowgraphs of reasonable size and only a few percent slower on very large flowgraphs.