Section: New Results

Copy Elimination on Data Dependence Graphs

Participants : Florian Brandner, Quentin Colombet.

Register allocation recently regained much interest due to new decoupled strategies that split the problem into separate phases: spilling, register assignment, and copy elimination.

A common assumption of existing copy elimination approaches is that the original ordering of the instructions in the program is not changed. We worked on an extension of a local recoloring technique that we developed earlier, called Parallel Copy Motion  [30] . We perform code motion on data dependence graphs in order to eliminate useless copies and reorder instructions, while at the same time a valid register assignment is preserved. Our results show that even after traditional register allocation with coalescing our technique is able to eliminate an additional 3% (up to 9%) of the remaining copies and reduce the weighted costs of register copies by up to 25% for the SPECINT 2000 benchmarks. In comparison to Parallel Copy Motion, our technique removes 11% (up to 20%) more copies and up to 39% more of the copy costs.

This work will be presented at the conference SAC'12 [6] .