NSan: A Floating-Point Numerical Sanitizer

TL;DR

NSan is a practical floating-point sanitizer integrated into LLVM that uses compile-time instrumentation with high-precision shadows to efficiently detect numerical issues, enabling routine use in testing and production.

Contribution

It introduces a fast, precise floating-point sanitizer within LLVM, significantly improving practicality over existing methods.

Findings

NSan is 1 to 4 orders of magnitude faster than existing approaches.

It provides precise, actionable feedback on floating-point issues.

NSan can be used routinely in unit tests and large applications.

Abstract

Sanitizers are a relatively recent trend in software engineering. They aim at automatically finding bugs in programs, and they are now commonly available to programmers as part of compiler toolchains. For example, the LLVM project includes out-of-the-box sanitizers to detect thread safety (tsan), memory (asan,msan,lsan), or undefined behaviour (ubsan) bugs. In this article, we present nsan, a new sanitizer for locating and debugging floating-point numerical issues, implemented inside the LLVM sanitizer framework. nsan puts emphasis on practicality. It aims at providing precise, and actionable feedback, in a timely manner. nsan uses compile-time instrumentation to augment each floating-point computation in the program with a higher-precision shadow which is checked for consistency during program execution. This makes nsan between 1 and 4 orders of magnitude faster than existing approaches, which allows running it routinely as part of unit tests, or detecting issues in large production applications.