Prime Path Coverage in the GNU Compiler Collection

TL;DR

This paper details the implementation of prime path coverage in GCC 15, a structural testing metric that balances thoroughness and testing effort, with improved algorithms for path enumeration and efficient path tracking.

Contribution

It introduces prime path coverage support in GCC 15, with novel algorithms for efficient path enumeration and a language-agnostic approach for coverage analysis.

Findings

Prime path coverage subsumes MC/DC.

Enhanced algorithms reduce path enumeration complexity.

Efficient path tracking using bitwise operations.

Abstract

We describe the implementation of the prime path coverage support introduced the GNU Compiler Collection 15, a structural coverage metric that focuses on paths of execution through the program. Prime path coverage strikes a good balance between the number of tests and coverage, and requires that loops are taken, taken more than once, and skipped. We show that prime path coverage subsumes modified condition/decision coverage (MC/DC). We improve on the current state-of-the-art algorithms for enumerating prime paths by using a suffix tree for efficient pruning of duplicated and redundant subpaths, reducing it to $O(n^2m)$ from $O(n^2m^2)$, where $n$ is the length of the longest path and $m$ is the number of candidate paths. We can efficiently track candidate paths using a few bitwise operations based on a compact representation of the indices of the ordered prime paths. By analyzing the control flow graph, GCC can observe and instrument paths in a language-agnostic manner, and accurately report what code must be run in what order to achieve coverage.