[Bug other/29694] New: missed warnings about comparisons which are always true/false.

[Bug other/29694] New: missed warnings about comparisons which are always true/false.

[pluto at agmk dot net]

unsigned foo( unsigned i )
{
        if ( i < 0 )
                i++;
        if ( i >= 0 )
                i++;
        return i;
}

g++ 412svn/420svn with `-O2 -Wall' reports no errors.


-- 
           Summary: missed warnings about comparisons which are always
                    true/false.
           Product: gcc
           Version: 4.2.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: other
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: pluto at agmk dot net
GCC target triplet: ix86-linux


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=29694

[Bug other/29694] missed warnings about comparisons which are always true/false.

[pinskia at gcc dot gnu dot org]

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------- Comment #1 from pinskia at gcc dot gnu dot org  2006-11-03 10:39 -------
Adding -W/-Wextra and we get a warning:
t.c: In function ‘foo’:
t.c:3: warning: comparison of unsigned expression < 0 is always false
t.c:5: warning: comparison of unsigned expression >= 0 is always true


I always forget what -Wextra is for.


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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=29694

[Bug other/29694] missed warnings about comparisons which are always true/false.

[pluto at agmk dot net]

------- Comment #2 from pluto at agmk dot net  2006-11-03 10:44 -------
(In reply to comment #1)
> Adding -W/-Wextra and we get a warning:
> t.c: In function �foo�:
> t.c:3: warning: comparison of unsigned expression < 0 is always false
> t.c:5: warning: comparison of unsigned expression >= 0 is always true
> 
> 
> I always forget what -Wextra is for.

what about -Walways-true ?

<man>

-Walways-true

   Warn about comparisons which are always true such as testing if
   unsigned values are greater than or equal to zero. This warning
   is enabled by -Wall.

</man>


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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=29694

[Bug other/29694] missed warnings about comparisons which are always true/false.

[manu at gcc dot gnu dot org]

------- Comment #3 from manu at gcc dot gnu dot org  2007-01-09 15:21 -------
Wextra warns for this, what is the bug?


-- 

manu at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |manu at gcc dot gnu dot org


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=29694

[Bug other/29694] missed warnings about comparisons which are always true/false.

[gdr at integrable-solutions dot net]

------- Comment #4 from gdr at integrable-solutions dot net  2007-01-09 18:41 -------
Subject: Re:  missed warnings about comparisons which are always true/false.

"manu at gcc dot gnu dot org" <gcc-bugzilla@gcc.gnu.org> writes:

| Wextra warns for this, what is the bug?

I believe pluto wants -Walways-true to cover this.

-- Gaby


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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=29694

[Bug other/29694] missed warnings about comparisons which are always true/false.

[manu at gcc dot gnu dot org]

------- Comment #5 from manu at gcc dot gnu dot org  2007-01-09 20:28 -------
(In reply to comment #4)
> Subject: Re:  missed warnings about comparisons which are always true/false.
> 
> "manu at gcc dot gnu dot org" <gcc-bugzilla@gcc.gnu.org> writes:
> 
> | Wextra warns for this, what is the bug?
> 
> I believe pluto wants -Walways-true to cover this.
> 

I pity the poor guy that implements that. Linus will surely kill him/her.


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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=29694

[Bug other/29694] missed warnings about comparisons which are always true/false.

[manu at gcc dot gnu dot org]

------- Comment #6 from manu at gcc dot gnu dot org  2007-01-20 16:30 -------
This is a duplicate of PR 23587.


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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=29694

[Bug other/29694] missed warnings about comparisons which are always true/false.

[pluto at agmk dot net]

------- Comment #7 from pluto at agmk dot net  2007-01-23 20:15 -------
(In reply to comment #4)
> Subject: Re:  missed warnings about comparisons which are always true/false.
> 
> "manu at gcc dot gnu dot org" <gcc-bugzilla@gcc.gnu.org> writes:
> 
> | Wextra warns for this, what is the bug?
> 
> I believe pluto wants -Walways-true to cover this.
> 
> -- Gaby

exactly.



*** This bug has been marked as a duplicate of 23587 ***


-- 

pluto at agmk dot net changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |RESOLVED
         Resolution|                            |DUPLICATE


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=29694

[Bug other/29694] missed warnings about comparisons which are always true/false.

[manu at gcc dot gnu dot org]

------- Comment #8 from manu at gcc dot gnu dot org  2007-05-20 21:31 -------
Subject: Bug 29694

Author: manu
Date: Sun May 20 20:29:55 2007
New Revision: 124875

URL: http://gcc.gnu.org/viewcvs?root=gcc&view=rev&rev=124875
Log:
2007-05-20  Manuel Lopez-Ibanez  <manu@gcc.gnu.org>

        PR middle-end/7651
        PR c++/11856
        PR c/12963
        PR c/23587
        PR other/29694
        * c.opt (Wtype-limits): New.
        * doc/invoke.texi (Wtype-limits): Document it.
        (Wextra): Enabled by -Wextra.
        * c-opts.c (c_common_post_options): Enabled by -Wextra.
        * c-common.c (shorten_compare): Warn with Wtype-limits.

testsuite/
        * gcc.dg/compare6.c: Replace Wall with Wtype-limits.
        * gcc.dg/Wtype-limits.c: New.
        * gcc.dg/Wtype-limits-Wextra.c: New.
        * gcc.dg/Wtype-limits-no.c: New.
        * g++.dg/warn/Wtype-limits.C: New.
        * g++.dg/warn/Wtype-limits-Wextra.C: New.
        * g++.dg/warn/Wtype-limits-no.C: New.

Added:
    trunk/gcc/testsuite/g++.dg/warn/Wtype-limits-Wextra.C
    trunk/gcc/testsuite/g++.dg/warn/Wtype-limits-no.C
    trunk/gcc/testsuite/g++.dg/warn/Wtype-limits.C
    trunk/gcc/testsuite/gcc.dg/Wtype-limits-Wextra.c
    trunk/gcc/testsuite/gcc.dg/Wtype-limits-no.c
    trunk/gcc/testsuite/gcc.dg/Wtype-limits.c
Modified:
    trunk/gcc/ChangeLog
    trunk/gcc/c-common.c
    trunk/gcc/c-opts.c
    trunk/gcc/c.opt
    trunk/gcc/doc/invoke.texi
    trunk/gcc/testsuite/ChangeLog
    trunk/gcc/testsuite/gcc.dg/compare6.c


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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=29694