Predicate execution provides a large number of opportunities to enhance and expose ILP in the presence of branches. However, as with speculative execution, an aggressive compiler is required to realize most of the performance advantages. Compiler Optimization and transformation techniques focus on eliminating branches from the instruction stream and overlapping the execution of multiple control flow paths using the conditional execution capabilities provided by predication. The compiler support for predicated execution is based on a new structure referred to as the hyperblock.. Hyperblocks are a generalized form of Superblock that takes advantage of both predicated and speculative execution. This paper discusses the hyperblock compilation techniques. The formation procedure of hyperblock is described first. Secondly, the extensions to traditional optimization, instruction scheduling, and register allocation techniques to enable them to work on hyperblocks. The presence of predicates introduces new challenges into the compiler backend to understand the meaning of predicates, take the advantage of the relations among predicates, and perform transformations in the presence of predicates. Finally, a set of four new optimizations designed specially for improving the performance of predicated code.

Abstract-Utilizing speculative execution alone to extract instruction level parallelism in the presence of branches has performance limitation .The fundamental limitation is that speculation eliminates dependencies between instructions and branches, but does not remove the branches themselves. To overcome this drawback, predicate execution is investigated. Predicate or guarded execution enables a compiler to eliminate branches from the instruction stream. As a result, many of the difficulties introduced by branches can be eliminated. This paper addresses the architectural support required to accomplish predicate execution. The architectural extensions required to provide efficient support for the predicated execution are discussed.Index Terms-Instruction level parallelism, nullification model, very long instruction word.