Formalizing Structured Control Flow Graphs.

Structured programs are believed to be easier to understand, and compiler friendly [5, 10, 45]. However, compilers do not process the source programs directly; they instead work on control flow graphs (CFGs) of the programs. Unfortunately, there is little formalization of structured CFGs. This paper shows how the lack of formalization has led to varying interpretations of structured CFGs. The paper next presents new formalization of structured CFGs which eliminates the ambiguity. Structured CFGs gain importance as they ease compiler optimizations, decompilation, and help reduce the performance degradation caused by thread divergence on SIMD units. The paper elaborates on these benefits. It also shows that compilers, both front-ends and back-ends, may generate unstructured CFGs from structured program sources, which necessitates mechanisms to obtain structured CFGs from unstructured ones.