Section: Software

LAO Developments in Aggressive Compilation

Participants : Benoit Boissinot, Florent Bouchez, Florian Brandner, Quentin Colombet, Alain Darte, Benoît Dupont de Dinechin [Kalray] , Christophe Guillon [stm icroelectronics] , Sebastian Hack [Former post-doc in Compsys] , Fabrice Rastello, Cédric Vincent [Former student in Compsys] .

Our aggressive optimization techniques are all implemented in stand-alone experimental tools (as for example for register coalescing algorithms) or within LAO, the back-end compiler of stm icroelectronics, or both. They concern SSA construction and destruction, instruction-cache optimizations, register allocation. Here, we report only our more recent activities, which concern register allocation.

Our developments on register allocation within the stm icroelectronics compiler started when Cédric Vincent (bachelor degree, under Alain Darte supervision) developed a complete register allocator in LAO, the assembly-code optimizer of stm icroelectronics. This was the first time a complete implementation was done with success, outside the mcdt (now cec ) team, in their optimizer. Since then, new developments are constantly done, in particular by Florent Bouchez, advised by Alain Darte and Fabrice Rastello, as part of his master internship and PhD thesis. In 2009, Quentin Colombet started to develop and integrate into the main trunk of LAO a full implementation of a two-phases register allocation. This implementation now includes two different decoupled spilling phases, the first one as described in Sebastian Hack's PhD thesis and a new ILP-based solution (see Section  6.2 ). It also includes an up-to-date graph-based register coalescing. Finally, since all these optimizations take place under SSA form, it includes also a mechanism for going out of colored-SSA (register-allocated SSA) form that can handle critical edges and does further optimizations (see for example Section  6.3 ).