PrediPrune: Reducing Verification Overhead in Souper with Machine Learning Driven Pruning

Abstract: Souper is a powerful enumerative superoptimizer that enhances the runtime performance of programs by optimizing LLVM intermediate representation (IR) code. However, its verification process, which relies on a computationally expensive SMT solver to validate optimization candidates, must explore a large search space. This large search space makes the verification process particularly expensive, increasing the burden to incorporate Souper into compilation tools. We propose PrediPrune, a stochastic candidate pruning strategy that effectively reduces the number of invalid candidates passed to the SMT solver. By utilizing machine learning techniques to predict the validity of candidates based on features extracted from the code, PrediPrune prunes unlikely candidates early, decreasing the verification workload. When combined with the state-of-the-art approach (Dataflow), PrediPrune decreases compilation time by 51% compared to the Baseline and by 12% compared to using only Dataflow, emphasizing the effectiveness of the combined approach that integrates a purely ML-based method (PrediPrune) with a purely non-ML based (Dataflow) method. Additionally, PrediPrune offers a flexible interface to trade-off compilation time and optimization opportunities, allowing end users to adjust the balance according to their needs.