[Bug c/45780] New: Warning for arithmetic operations involving C99 _Bool variable

[Bug c/45780] New: Warning for arithmetic operations involving C99 _Bool variable

[ubizjak at gmail dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=45780

           Summary: Warning for arithmetic operations involving C99 _Bool
                    variable
           Product: gcc
           Version: 4.5.2
            Status: UNCONFIRMED
          Severity: enhancement
          Priority: P3
         Component: c
        AssignedTo: unassigned@gcc.gnu.org
        ReportedBy: ubizjak@gmail.com


Pasted from the thread that introduced _Bool in place of "GCC bool":

<quote>

> >> It can be done ultimately, but as a prerequisite, we should have
> >> warnings in -Wextra for all of
> >>
> >> ? boolvar++; ++boolvar;
> >> ? boolvar--; --boolvar;
> >> ? boolvar = nonbool;
> >> ? boolvar & nonbool; boolvar &= nonbool;
> >> ? boolvar | nonbool; boolvar |= nonbool;
> >> ? boolvar ^ nonbool; boolvar ^= nonbool;
> >
> > Fair enough. I have CCed Manuel, perhaps he is interested in this warning.
> 
> I am not sure it fits in -Wconversion. -Wbool-arith perhaps?

It sounds like a warning for a -Wc90-c99-compat or similar option 
(possibly in a more specific option such as -Wbool-arith) - pure C99 code 
has little use for such a warning, it's about code that might be compiled 
either with C99 _Bool, or with C90 unsigned char, and so needs to avoid 
cases where they are incompatible.  Such an option, similar in spirit to 
-Wtraditional, could also allow you to get warnings in C99 mode for things 
currently diagnosed with -std=c90 -pedantic.

</quote>

[1] http://gcc.gnu.org/ml/gcc-patches/2010-09/msg01941.html

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[Bug c/45780] Warning for arithmetic operations involving C99 _Bool variable

[ubizjak at gmail dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=45780

Uros Bizjak <ubizjak at gmail dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |NEW
   Last reconfirmed|                            |2010.09.24 18:44:45
               date|                            |
            Version|4.5.2                       |unknown
     Ever Confirmed|0                           |1

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[Bug c/45780] Warning for arithmetic operations involving C99 _Bool variable

[ericb at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=45780

Eric Blake <ericb at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |ericb at gcc dot gnu.org

--- Comment #1 from Eric Blake <ericb at gcc dot gnu.org> 2010-11-03 20:05:00 UTC ---
Don't forget a warning on implicit conversions from int to bool, such as:

bool f(int i) { return i; }

although it might make sense to avoid warnings on provably 0/1 int conversion
to bool, as in:

bool f(int i) { i = !!i; return i; }

[Bug c/45780] Warning for arithmetic operations involving C99 _Bool variable

[egall at gwmail dot gwu.edu]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=45780

Eric Gallager <egall at gwmail dot gwu.edu> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |egall at gwmail dot gwu.edu

--- Comment #2 from Eric Gallager <egall at gwmail dot gwu.edu> ---
The -Wc90-c99-compat that made it into gcc5 currently warns about any usage of
bool whatsoever, not just the specific usages of bool listed in this bug...

[Bug c/45780] Warning for arithmetic operations involving C99 _Bool variable

[egall at gwmail dot gwu.edu]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=45780

--- Comment #4 from Eric Gallager <egall at gwmail dot gwu.edu> ---
(In reply to Marek Polacek from comment #3)
> (In reply to Eric Gallager from comment #2)
> > The -Wc90-c99-compat that made it into gcc5 currently warns about
> > any usage of bool whatsoever, not just the specific usages of bool
> > listed in this bug...
> 
> Right, that was the point of it.

...so is this bug worth keeping open then? It'd seem kinda redundant to me for
extra, more-specific warnings about bools to be placed in -Wc90-c99-compat (as
was originally proposed), when the flag already prints the more-generalized
warnings that it currently does. Or would they get their own separate
-Wbool-arith option? If so, what would happen when a user specifies both a
hypothetical -Wbool-arith flag along with -Wc90-c99-compat at the same time?
I'm just kinda worried that such a situation could lead to duplicated and/or
excessive warnings...