The emerging hardware support for thread-level speculation opens new opportunities to parallelize sequential programs beyond the traditional limits. By speculating that many data dependences are unlikely during runtime, consecutive iterations of a sequential loop can be executed speculatively in parallel. Runtime parallelism is obtained when the speculation is correct. To take full advantage of this new execution model, a program needs to be programmed or compiled in such a way that it exhibits high degree of speculative thread-level parallelism. We propose a comprehensive cost-driven compilation framework to perform speculative parallelization. Based on a misspeculation cost model, the compiler aggressively transforms loops into optimal speculative parallel loops and selects only those loops whose speculative parallel execution is likely to improve program