A General Compiler Framework for Data Speculation Using DSCM

Abstract

Getting precise alias information in a language that allows pointers, such as C, is expensive. One reason is that alias analysis should generate conservative (safe) alias information. Alias analysis assumes possible aliases when it can’t prove there are no aliases. The conservativealias information may greatly affect compiler optimizations. In this paper, we present a general framework to allow speculative (unsafe) alias information to be used in several compiler optimizations such as redundancy elimination, copy propagation, dead store elimination and code scheduler. Speculative alias information is not guaranteed to be correct. Run-time verification and recovery code are generated to guarantee the correctness of the optimizations that use speculative alias information. In the framework, the key idea is to use data speculative code motion (DSCM) to move the instruction that will be optimized away to the instruction that causesthe optimization. During DSCM, verification and recovery code are generated. After the DSCM, the optimization becomes non-speculative and the moved instruction can be optimized away.