Unification of Static and Dynamic Analyses to Enable Vectorization.

Modern compilers execute sophisticated static analyses to enable optimization across a wide spectrum of code patterns. However, there are many cases where even the most sophisticated static analysis is insufficient or where the computation complexity makes complete static analysis impractical. It is often possible in these cases to discover further opportunities for optimization from dynamic profiling and provide this information to the compiler, either by adding directives or pragmas to the source, or by modifying the source algorithm or implementation. For current and emerging generations of chips, vectorization is one of the most important of these optimizations. This paper defines, implements, and applies a systematic process for combining the information acquired by static analysis by modern compilers with information acquired by a targeted, high-resolution, low-overhead dynamic profiling tool to enable additional and more effective vectorization. Opportunities for more effective vectorization are frequent and the performance gains obtained are substantial: we show a geometric mean across several benchmarks of over 1.5x in speedup on the Intel Xeon Phi coprocessor.