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From: "segher at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
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Subject: [Bug c/104711] Unnecessary -Wshift-negative-value warning
Date: Sun, 27 Feb 2022 22:37:08 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D104711

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 =E2=80=98<<=E2=80=99 as u=
ndefined. However,
  -fsanitize=3Dshift (and -fsanitize=3Dundefined) 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 thi=
s,
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 positi=
ves,
detection of serious problems, and usefulness to be included in -Wextra.  T=
he
considerations for -Wall and -W are exactly the same, just the bar is lower=
 for
the latter.

Confirmed.=