Code Bones: Fast and Flexible Code Generation for Dynamic and Speculative Polyhedral Optimization

In this paper, we present a new runtime code generation technique for speculative loop optimization and parallelization, that allows to generate on-the-fly codes resulting from any polyhedral optimizing transformation of loop nests, such as tiling, skewing, fission, fusion or interchange, without introducing a penalizing time overhead. The proposed strategy is based on the generation of code bones at compile-time, which are parametrized code snippets either dedicated to speculation management or to computations of the original target program. These code bones are then instantiated and assembled at runtime to constitute the speculatively-optimized code, as soon as an optimizing polyhedral transformation has been determined. Their granularity threshold is sufficient to apply any polyhedral transformation, while still enabling fast runtime code generation. This strategy has been implemented in the speculative loop parallelizing framework Apollo.