[Bug c/104711] Unnecessary -Wshift-negative-value warning

["segher at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=104711

Segher Boessenkool <segher at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Last reconfirmed|                            |2022-02-27
     Ever confirmed|0                           |1
             Status|UNCONFIRMED                 |NEW

--- Comment #2 from Segher Boessenkool <segher at gcc dot gnu.org> ---
Our documentation says in
<https://gcc.gnu.org/onlinedocs/gcc/Integers-implementation.html>

  As an extension to the C language, GCC does not use the latitude given in C99
  and C11 only to treat certain aspects of signed ‘<<’ as undefined. However,
  -fsanitize=shift (and -fsanitize=undefined) will diagnose such cases. They
are
  also diagnosed where constant expressions are required.

It would be much saner / much more practical if we actually implemented this,
i.e. don't have -Wshift-negative-value in -Wextra (the above text does not make
much sense if that was the design!)

This warning does have a good enough balance between amount of false positives,
detection of serious problems, and usefulness to be included in -Wextra.  The
considerations for -Wall and -W are exactly the same, just the bar is lower for
the latter.

Confirmed.