alt Hacker NewsA lot of compilers will optimize out a NULL pointer check because dereferencing a NULL pointer is UB.
Because assert will not run the following code in the case of a NULL pointer, AFAIK this exact code is still defined behavior, but if for some reason some code dereferenced the NULL pointer before, it would be optimized out - there are some corner cases that aren't obvious on the surface.
This kind of thing was always theoretically allowed, but really started to become insidious within the past 5-10 years. It's probably one of the more surprising UB things that bites people in the field.
GCC has a flag "-fno-delete-null-pointer-checks" to specifically turn off this behavior.
https://qinsb.blogspot.com/2018/03/ub-will-delete-your-null-...
This is an actual Linux kernel exploit caused by this behavior where the compiler optimized out code that checked for a NULL pointer and returned an error.
Sure, but none of that is relevant to just the code snippet that was posted. The compiler can exploit UB in other code to do weird things, but that's just C being C. There's nothing unexpected in the snippet posted.
The issue is cause by C declaring that dereferencing a null pointer is UB. It's not really an issue with assertions.
You can get the same optimisation-removes-code for any UB.