Maintaining Canonical Form After Edge Deletion

Abstract

Waddle is a research intermediate-form optimizer that strictly maintains a canonical form similar to the loop-simplify form used in LLVM. The properties of this canonical form simplify movement of instructions to the edges of loops and often localize the effect on variables to the loop in which they are defined. The guarantee of canonical form preservation allows program transformations to rely on the presence of certain program properties without a necessary sanity-check or recalculation pre-step and does not impose an order of transformations in which reconstruction passes must be inserted. In this paper, we present a form-preserving edge deletion operation, in which a provably unreachable branch between two basic blocks is removed from the control flow graph. Additionally, we showa distinct application of the block ejection operation, a core procedure used for loop body reconstruction, as utilized in a function inlining transformation.