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We present a new algorithm for dynamic memory disambiguation for array references that allows us to overcome limitations of static analysis. For array references that cannot be accurately analyzed at compile time, we defer the disambiguation process until run-time. We have implemented our analysis algorithm in a prototype version of the IBM XL compiler and used the generated information for several compiler optimizations: software pipelining with global instruction scheduling, loop-invariant motion and redundant load elimination. We evaluated the algorithm on an IBM POWER2 system using the SPEC92 benchmarks. We show that for numeric C benchmarks, dynamic memory disambiguation can greatly improve run-time performance. Perhaps more importantly, we show that even for the programs that cannot benefit from dynamic analysis, the overhead of our algorithm does not degrade performance.