Compiler optimization techniques for OpenMP programs

In this paper, we present some compiler optimization techniques for explicit parallel programs using OpenMP API. To enable optimizations across threads, we designed data ow analysis techniques in which interaction between threads is e ectively modeled. Structured description of parallelism and relaxed memory consistency in OpenMP make the analyses e ective and eÆcient. We show algorithms for reaching de nitions analysis, memory synchronization analysis, and cross-loop data dependence analysis for parallel loops. Our primary target is a compiler-directed software DSM system where aggressive compiler optimizations for software-implemented coherence scheme are crucial to obtain good performance. We also show optimizations applicable to general OpenMP implementations, namely redundant barrier removal and privatization of dynamically allocated objects. We consider compiler optimizations are bene cial for performance portability across various platforms and non-expert programmers. Experimental results for the coherency optimization in a compilerdirected software DSM system shows that aggressive compiler optimizations are quite e ective for a shared-write intensive program because coherenceinduced communication volume in such a program is much larger than the those for shared-read intensive programs.