A Detailed Analysis of the LLVM´s Register Allocators

The goal of a register allocation is to allocate a unbounded amount of program values to a finite amount of machine registers, which is an issue that impacts the performance of the final code. Thus, a good register allocator has the goal of minimizing the amount of program values that should be represented in memory. This paper presents a detailed analysis of the register allocators provides by LLVM framework, namely: fast, basic, greedy, and PBQP. The analysis was conducted to evaluate runtime, compile time and the amount of spills. Furthermore, hardware performance counters were analyzed in order to describe in more detail the behavior of the register allocators. The results demonstrated that greedy register allocator it the best one for minimizing the runtime and the amount of spills, otherwise the basic and fast are the best choice for compile time.