Coalescing Conditional Branches into Efficient Indirect Jumps

Indirect jumps from tables are traditionally only generated by compilers as an intermediate code generation decision when translating multiway selection statements. However, making this decision during intermediate code generation poses problems. The research described in this paper resolves these problems by using several types of static analysis as a framework for a code improving transformation that exploits indirect jumps from tables. First, control-flow analysis is performed that provides opportunities for coalescing branches generated from other control statements besides multiway selection statements. Second, the optimizer uses various techniques to reduce the cost of indirect jump operations by statically analyzing the context of the surrounding code. Finally, path and branch prediction analysis is used to provide a more accurate estimation of the benefit of coalescing a detected set of branches into a single indirect jump. The results indicate that the coalescing transformation can be frequently applied with significant reductions in the number of instructions executed and total cache work. This paper shows that static analysis can be used to implement an effective improving transformation for exploiting indirect jumps