A systematic integration of register allocation and instruction scheduling

In order to achieve high performance, processor architecture has become more and more complicated. As a result, compiler-time optimizations have become more and more important for the effective use of a complex processor. One of the promising compiler-time optimizations is the integration of register allocation and instruction scheduling based on register-reuse chains. In the previous approach, however, the generation of register-reuse chains was not completely systematic and consequently created many unnecessary dependencies that restrict instruction scheduling. This research proposes a new register allocation technique based on a systematic generation of register-reuse chains. The first phase of the proposed technique is to generate register-reuse chains that are optimal in the sense that no additional dependencies are created. Thus, register allocation can be done without restricting instruction scheduling. For the case when the optimal register-reuse chains require more than available registers, the second phase reduces the number of required registers by merging the register-reuse chains. A heuristic is developed for the second phase in order to reduce the additional dependencies created by merging chains. The first step of the second phase is to derive a conflict graph in which each node corresponds to a register-reuse chain, while an edge represents where the corresponding two chains cannot be merged. Applying a graph-coloring algorithm to the conflict graph, the number of chains can be effectively reduced. The final step of the second phase is to run the 0-1 knapsack algorithm to make the number of chains exactly the same as the number of available registers. The proposed register allocation is implemented in LCC (Local C Compiler). An instruction scheduler is also implemented in LCC and then integrated with the proposed register allocator. Evaluation results show that the proposed algorithm and heuristic effectively reduce the number of necessary registers

A Modified Optical Image Reconstruction Model With Information Feedback

The significant computational overhead associated with the iterative reconstruction process of biomedical optical imaging is one of the major factors that hinder its application in clinical diagnosis, especially for large tissue volumes. Based on previous studies, the paper presents a general purpose biomedical optical image reconstruction model along with components and data flow diagram, and proposes a modified model taking into account the information feedback during the iterative image reconstruction process to control the image resolution in the subdomain of interest, and hence to detect interior targets, such as tumors, from the discrete measurements collected on the surface of clinically relevant tissue. The modified image reconstruction model (MIRM) may provide a means to detect small targets and improve the image quality at relatively low computational cost