Abstract. This paper deals with coalescing in SSA-based register allo-cation. Current coalescing techniques all require the interference graph to be built. This is generally considered to be too compile-time intensive for just-in-time compilation. In this paper, we present a biased coloring approach that gives results similar to standalone coalescers while signif-icantly reducing compile time. 1

In compilation, register allocation is the optimization that chooses which variables of the source program, in unlimited number, are mapped to the actual registers, in limited number. Parts of the live-ranges of the variables that cannot be mapped to registers are placed in memory. This eviction is called spilling. Until recently, compilers mainly addressed register allocation via graph coloring using an idea developed by Chaitin et al. [33] in 1981. This approach addresses the spilling and the mapping of the variables to registers in one phase. In 2001, Appel and George [3] proposed to split the register allocation in two separate phases. This idea yields better and independent solutions for both problems, but requires a very aggressive form of live-range splitting, split everywhere, which renames all variables between all instructions of the program. However, in 2005, several groups [27, 84, 56, 16] observed that the static single assignment (SSA) form provides sufficient split points to decouple the register allocation as Appel and George suggested, unless register aliasing or precoloring constraints are involved.

HAL is a multi-disciplinary open access archive for the deposit and dissemination of sci-entific research documents, whether they are pub-lished or not. The documents may come from teaching and research institutions in France or abroad, or from public or private research centers. L’archive ouverte pluridisciplinaire HAL, est destinée au dépôt et a ̀ la diffusion de documents scientifiques de niveau recherche, publiés ou non, émanant des établissements d’enseignement et de recherche français ou étrangers, des laboratoires publics ou privés. appor t de r ech er ch e

Abstract not found