Beautifully explained!

UB is a formal tool for the optimizer.

Most people who argue about UB on HN have no clue wth it means and how it differs from Unspecified and Implementation-defined behaviours. The standard already explains expressions/statements and how they relate to sequence-points/sequenced-before/sequenced-after code points which is what is needed to understand the anomalous behaviour above.

Add in a introductory class in numerical analysis w.r.t. accuracy/precision/limits/rounding and the C/C++ programmer has enough knowledge to avoid problems in practice.