cc-ing relevant people

came up on gcc-help here: https://gcc.gnu.org/ml/gcc-help/2018-10/msg00051.html

At least some of these prevent enabling -Wnull-dereference with -Wextra.

At least some of what?  I don't follow.  _Is_ there anything that prevents
us from enabling -Wnull-dereference at -Wextra or -Wall or even by default?
Does it have false positives?

(In reply to Segher Boessenkool from comment #4)
> At least some of what?  I don't follow.

The bugs that this one depends upon.

> _Is_ there anything that prevents us from enabling -Wnull-dereference at
> -Wextra or -Wall or even by default?

It was previously in -Wall, but it was removed from it in r226751 because it broke bootstrap, see bug 16351 comment 35. 

> Does it have false positives?

Bug 71157 is a false positive.

Thanks for the information Eric.

Will it help if the option is split into -Wnull-dereference and
-Wmaybe-null-dereference (as suggested before)?

(In reply to Segher Boessenkool from comment #6)
> Thanks for the information Eric.
> 
> Will it help if the option is split into -Wnull-dereference and
> -Wmaybe-null-dereference (as suggested before)?

This discussion is now in bug 96554