Section: New Results

Function Cloning Revisited

Participants : Matheus Vilela [UFMG, Belo Horizonte, Brazil] , Guilherme Balena [UFMG, Belo Horizonte, Brazil] , Guilherme Marques [UFMG, Belo Horizonte, Brazil] , Fernando Magno Quintão Pereira [UFMG, Belo Horizonte, Brazil] , Fabrice Rastello.

Compilers rely on two main techniques to implement optimizations that depend on the calling context of functions: inlining and cloning. Historically, function inlining has seen more widespread use, as it tends to be more effective in practice. Yet, function cloning provides benefits that inline leaves behind. In particular, cloning gives the program developer a way to fight performance bugs, because it generates reusable code. Furthermore, it deals with recursion more naturally. Finally, it might lead to less code expansion, the inlining's nemesis.

In this work, we revisited function cloning under the light of these benefits. We discuss four independent code specialization techniques based on function cloning, which, although simple, find wide applicability, even in highly optimized benchmarks, such as SPEC CPU 2006. We claim that our optimizations are easy to implement and to deploy. We use Wu and Larus's well-known static profiling heuristic to measure the profitability of a clone. This metric gives us a concrete way to point out to program developers potential performance bugs, and gives us a metric to decide if we should keep a clone or not. By implementing our ideas in LLVM, we have been able to speed up some of the SPEC benchmarks by up to 6% on top of the -O2 optimization level.

This work is part of the collaboration with UFMG (see Section  8.4 ) and was also done in the context of the collaboration with Kalray and the ManycoreLabs project (see Section  7.2 ).