Fully Dynamic Maintenance of Loop Nesting Forests in Reducible Flow Graphs

TL;DR

This paper introduces the first fully dynamic algorithm for maintaining loop nesting forests in reducible flow graphs, enabling efficient updates during control-flow graph modifications.

Contribution

It leverages recent dynamic DFS techniques to incrementally update loop structures, avoiding global recomputation and improving efficiency in compiler analyses.

Findings

Supports edge insertions and deletions efficiently

Local updates confine changes to small regions

Enables fast derivation of dominance information

Abstract

Loop nesting forests (LNFs) are a fundamental abstraction for reasoning about control-flow structure, enabling applications such as compiler optimizations, program analysis, and dominator computation. While efficient static algorithms for constructing LNFs are well understood, maintaining them under dynamic graph updates has remained largely unexplored due to the lack of efficient dynamic depth-first search (DFS) maintenance. In this paper, we present the first fully dynamic algorithm for maintaining loop nesting forests in reducible control-flow graphs. Our approach leverages recent advances in dynamic DFS maintenance to incrementally update loop structure under edge insertions and deletions. We show that updates can be confined to local regions of the depth-first spanning tree, avoiding global recomputation. We provide formal invariants, correctness arguments, and complexity analysis, and demonstrate how the maintained LNF enables efficient derivation of dominance information. Our results establish LNFs as a practical dynamic abstraction for modern compiler and analysis pipelines.