Yes, UB is actually that Bad (The Day GCC Broke Chrome)

[lefticus]

https://stackoverflow.com/questions/36893251/why-does-the-enhanced-gcc-6-optimizer-break-practical-c-code

https://gaultier.github.io/blog/the_production_bug_that_made_me_care_about_undefined_behavior.html

Note that ubsan doesn't catch this:

https://compiler-explorer.com/z/z8jx73ncf

And the classic:

https://compiler-explorer.com/z/bMGrsrEWs

[lefticus]