[Bug sanitizer/79265] [7 regression] -fsanitize=undefined inserts unnecessary null pointer tests

[sirl at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=79265

--- Comment #6 from Franz Sirl <sirl at gcc dot gnu.org> ---
(In reply to Jakub Jelinek from comment #4)
> This is a new warning, the fact that we didn't warn on some code and now
> warn with a new warning is not necessarily a regression.

Well, I wasn't so sure either if it counts as a regression, that's why I asked
on IRC first and then changed it. If you feel otherwise, you can remove the
marker again.

I guess it is kind of a "usability regression":

- "gcc-6 -Wall -Werror": compiles
- "gcc-6 -Wall -Werror -fsanitize=undefined": compiles
- "gcc-7 -Wall -Werror": compiles
- "gcc-7 -Wall -Werror -fsanitize=undefined": doesn't compile because of false
warning

So it's no longer enough to "just add -fsanitize=undefined" and recompile, now
you have to adjust warnings as well.

If it can't be reasonably solved within the GCC-7 timeframe, I would be fine
with a stop-gap measure like removing -Wformat-overflow from -Wall when UBSAN
is active (for example).