Struct-reorg: current status and future perspectives

In this paper we present the ongoing effort to implement C structure optimizations in GCC, its current status and future plans. The general idea of this set of optimizations is to adapt the layout of a data-structure to its access patterns in order to better utilize the cache by increasing spatial locality. These optimizations are known to have many variations and require wide va-riety of data to be analyzed. An initial imple-mentation of these optimizations in GCC was presented at the GCC Developers ’ Summit of 2005. Since then many changes took place, in-cluding updating to Tree-SSA and preparation for GCC mainline 4.3. Additional opportuni-ties were revealed after close analysis of mcf benchmark from Spec2000/Spec20061. Struct-reorg relies on careful type escape analysis ca-pabilities, which were provided by K. Zadeck and are now being enhanced to really utilize the Tree-SSA form. In addition, as this type of op-timization requires the scope of whole program to be analyzed, it is a natural candidate to lever-age the LTO effort. To prepare its transition to this level, we present optimization flow of data collection stage of struct-reorg optimiza-tions from an LTO perspective. 1In the context of this paper mcf benchmark equally represents both 181.mcf benchmark from Spec2000 and 429.mcf from Spec2006