Restrictification of function arguments

Abstract

Pointer aliasing still hinders compiler optimizations, despite years of research on pointer disambiguation. Several programming languages offer to coders mechanisms to distinguish memory references, such as the 'restrict' keyword in C. However, the use of such mechanisms is prone to human mistakes. This work presents a suite of automatic techniques that mitigate this problem: three different ways to disambiguate pointers passed as arguments of functions. These techniques combine static analyses to infer symbolic bounds of memory regions and code versioning. Functions whose pointers are distinct can be aggressively optimized whereas they wouldn't otherwise. An implementation of the restrictification methods in the LLVM compiler shows that we can vectorize up to 63% more operations than what could be accomplished using the highest optimization level of said compiler. When applying the optimization on OpenCV benchmarks, a widely used library, we have observed speedups as great as 40%.