The Perils of Fast Math Compiler Flags

This article delves into the potential dangers of the 'fast-math' compiler flag, a common optimization that can significantly speed up mathematical computations but at the cost of accuracy. The author details several pitfalls associated with flags like `-ffast-math` in GCC, including the removal of NaN and Inf checks, reassociation of floating-point operations, and the enabling of Flush-to-Zero (FTZ). These optimizations, while seemingly innocuous, can lead to subtle and difficult-to-debug errors. The article advocates for a cautious approach to using fast-math, suggesting thorough testing and selective application of specific optimizations. It concludes with a call for improved compiler and language features to provide safer, more granular control over these optimizations, moving away from the blunt instrument of a single compiler flag and towards more sophisticated mechanisms.