Dependence-Conscious Global Register Allocation

Wolfgang Ambrosch and M. Anton Ertl and Felix Beer and Andreas Krall
Institut für Computersprachen
Technische Universität Wien
Argentinierstraße 8
A-1040 Wien, Austria


Register allocation and instruction scheduling are antagonistic optimizations: Whichever is applied first, it will impede the other. To solve this problem, we propose dependence-conscious colouring, a register allocation method that takes the dependence graph used by the instruction scheduler into consideration. Dependence-conscious colouring consists of two parts: First, the interference graph is built by analysing the dependence graphs, resulting in fewer interference edges and less spilling than the conventional preordering approach. Secondly, during colouring the register selection keeps dependence paths short, ensuring good scheduling. Dependence-conscious colouring reduces the number of interference edges by 7%--24% and antidependences by 46%-100%.