If you're passing the pointer to the standard library's `free()` then the compiler doesn't actually have to worry about pointer aliasing - it's undefined behavi

If you're passing the pointer to the standard library's `free()` then the compiler doesn't actually have to worry about pointer aliasing - it's undefined behavior to use a pointer after it has been passed to `free()`, so it can conclude it never happens in your program. FWIW most of what you're referring to (reaching a free'd pointer via pointer arithmetic, or going straight to its address) is actually undefined behavior according to the C standard, what you're allowed to do with pointers is more limited than that. There are ways of getting around some of that (obviously, since it's necessary in embedded and other low-level situations), but it requires knowledge about your specific compiler and/or potentially the use of extensions or similar things not part of the standard.