[Bug c/32061] New: wrong warning wording

[Bug c/32061] New: wrong warning wording

[eyal at eyal dot emu dot id dot au]

This warning is logically incorrect:
  logical '&&' with non-zero constant will always evaluate as true
should say '... will have no effect'?

Reproduce with
==============
/* run: gcc -v -save-temps -Wlogical-op -c xx.c
*/
#define FORCE   1
#define FLAG    1
static int func (int resp, int flags)
{
  return (resp && (FORCE || (FLAG & flags)));
}

output
======
Using built-in specs.
Target: i686-pc-linux-gnu
Configured with: /usr/local/src/gcc/src/gcc-current/configure
--srcdir=/usr/local/src/gcc/src/gcc-current --prefix=/usr/local/gcc-current
--enable-languages=c,c++ --with-mpfr=/usr/local/mpfr --with-gmp=/usr/local/gmp
Thread model: posix
gcc version 4.3.0 20070518 (experimental)

/data2/usr/local/gcc-current-20070519-083055/bin/../libexec/gcc/i686-pc-linux-gnu/4.3.0/cc1
-E -quiet -v -iprefix
/data2/usr/local/gcc-current-20070519-083055/bin/../lib/gcc/i686-pc-linux-gnu/4.3.0/
xx.c -mtune=generic -Wlogical-op -fpch-preprocess -o xx.i
ignoring nonexistent directory
"/data2/usr/local/gcc-current-20070519-083055/bin/../lib/gcc/i686-pc-linux-gnu/4.3.0/../../../../i686-pc-linux-gnu/include"
ignoring duplicate directory
"/data2/usr/local/gcc-current-20070519-083055/bin/../lib/gcc/../../lib/gcc/i686-pc-linux-gnu/4.3.0/include"
ignoring duplicate directory
"/data2/usr/local/gcc-current-20070519-083055/bin/../lib/gcc/../../lib/gcc/i686-pc-linux-gnu/4.3.0/include-fixed"
ignoring nonexistent directory
"/data2/usr/local/gcc-current-20070519-083055/bin/../lib/gcc/../../lib/gcc/i686-pc-linux-gnu/4.3.0/../../../../i686-pc-linux-gnu/include"
#include "..." search starts here:
#include <...> search starts here:

/data2/usr/local/gcc-current-20070519-083055/bin/../lib/gcc/i686-pc-linux-gnu/4.3.0/include

/data2/usr/local/gcc-current-20070519-083055/bin/../lib/gcc/i686-pc-linux-gnu/4.3.0/include-fixed
 /usr/local/include
 /data2/usr/local/gcc-current-20070519-083055/bin/../lib/gcc/../../include
 /usr/include
End of search list.

/data2/usr/local/gcc-current-20070519-083055/bin/../libexec/gcc/i686-pc-linux-gnu/4.3.0/cc1
-fpreprocessed xx.i -quiet -dumpbase xx.c -mtune=generic -auxbase xx
-Wlogical-op -version -o xx.s
GNU C version 4.3.0 20070518 (experimental) (i686-pc-linux-gnu)
        compiled by GNU C version 4.3.0 20070518 (experimental), GMP version
4.2.1, MPFR version 2.2.1.
warning: GMP header version 4.2.1 differs from library version 4.1.4.
GGC heuristics: --param ggc-min-expand=30 --param ggc-min-heapsize=4096
Compiler executable checksum: 128b6cbfc01a7daaa897672777a1e4cb
xx.c: In function 'func':
xx.c:7: warning: logical '&&' with non-zero constant will always evaluate as
true
 as -V -Qy -o xx.o xx.s
GNU assembler version 2.15 (i386-linux) using BFD version 2.15


-- 
           Summary: wrong warning wording
           Product: gcc
           Version: 4.3.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: eyal at eyal dot emu dot id dot au


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=32061

[Bug c/32061] wrong warning wording

[pinskia at gcc dot gnu dot org]

------- Comment #1 from pinskia at gcc dot gnu dot org  2007-05-24 00:47 -------
I don't see the problem because
"xx.c:7: warning: logical '&&' with non-zero constant will always evaluate as
true"
means the non-zero constant will evaluate as true and not the logical will
evaluate as true.


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=32061

[Bug c/32061] wrong warning wording

[eyal at eyal dot emu dot id dot au]

------- Comment #2 from eyal at eyal dot emu dot id dot au  2007-05-24 01:00 -------
(In reply to comment #1)
> I don't see the problem because
> "xx.c:7: warning: logical '&&' with non-zero constant will always evaluate as
> true"
> means the non-zero constant will evaluate as true and not the logical will
> evaluate as true.
> 

(In reply to comment #1)
> I don't see the problem because
> "xx.c:7: warning: logical '&&' with non-zero constant will always evaluate as
> true"
> means the non-zero constant will evaluate as true and not the logical will
> evaluate as true.
> 

But it says 'logical... will always evaluate as true' which clearly refers to
the result of the logical operator, not to one of its arguments.

BTW, why no warning for this?
   resp == 0 && 0
Naturally, all the above constants will hide behind some macros which could
indicate a real error, hence the value of the warning.


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=32061

[Bug c/32061] (Wlogical-op) wording of warning of constant logicials need improvement

[manu at gcc dot gnu dot org]

------- Comment #3 from manu at gcc dot gnu dot org  2009-02-11 23:04 -------
Confirmed. I have a patch for this for 4.5.

The new wording will say:

warning: logical 'or' applied to non-boolean constant.

Are you satisfied with this?

> 
> BTW, why no warning for this?
>    resp == 0 && 0
> Naturally, all the above constants will hide behind some macros which could
> indicate a real error, hence the value of the warning.

Warning for (x && 0) or (x && 1) would produce hundreds of false positives. We
shouldn't warn about your testcase either.


-- 

manu at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |manu at gcc dot gnu dot org
             Status|UNCONFIRMED                 |NEW
     Ever Confirmed|0                           |1
   Last reconfirmed|0000-00-00 00:00:00         |2009-02-11 23:04:41
               date|                            |
            Summary|wording of warning of       |(Wlogical-op) wording of
                   |constant logicials need     |warning of constant
                   |improvement                 |logicials need improvement


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=32061

[Bug c/32061] (Wlogical-op) wording of warning of constant logicials need improvement

[eyal at eyal dot emu dot id dot au]

------- Comment #4 from eyal at eyal dot emu dot id dot au  2009-02-12 08:28 -------
(In reply to comment #3)
> Confirmed. I have a patch for this for 4.5.
> 
> The new wording will say:
> 
> warning: logical 'or' applied to non-boolean constant.
> 
> Are you satisfied with this?

Great, thanks.


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=32061

[Bug c/32061] (Wlogical-op) wording of warning of constant logicials need improvement

[manu at gcc dot gnu dot org]

------- Comment #5 from manu at gcc dot gnu dot org  2009-02-18 13:13 -------
Patch submitted: http://gcc.gnu.org/ml/gcc-patches/2009-02/msg00824.html


-- 

manu at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                URL|                            |http://gcc.gnu.org/ml/gcc-
                   |                            |patches/2009-
                   |                            |02/msg00824.html
           Keywords|                            |patch


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=32061

[Bug c/32061] (Wlogical-op) wording of warning of constant logicials need improvement

[manu at gcc dot gnu dot org]

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------- Comment #6 from manu at gcc dot gnu dot org  2009-04-19 11:04 -------
Subject: Bug 32061

Author: manu
Date: Sun Apr 19 11:04:13 2009
New Revision: 146344

URL: http://gcc.gnu.org/viewcvs?root=gcc&view=rev&rev=146344
Log:
2009-04-19  Manuel López-Ibáñez  <manu@gcc.gnu.org>

        PR c/32061
        PR c++/36954
        * doc/invoke.texi: Add -Wlogical-op to -Wextra.
        * common.opt (Wlogical-op): Move from here...
        * c.opt (Wlogical-op): ... to here.
        * c-typeck.c (parser_build_binary_op): Update call to
        warn_logical_operator.
        * c-opts.c (c_common_post_options): Enable warn_logical_op with
        extra_warnings.
        * c-common.c (warn_logical_op): Update.
        * c-common.h (warn_logical_op): Update declaration.
cp/
        * call.c (build_new_op): Save the original codes of operands
        before folding.

testsuite/
        * gcc.dg/pr32061.c: New.
        * gcc.dg/Wlogical-op-1.c: Update.
        * g++.dg/warn/Wlogical-op-1.C: Update.
        * g++.dg/warn/pr36954.C: New.

Added:
    trunk/gcc/testsuite/g++.dg/warn/pr36954.C
    trunk/gcc/testsuite/gcc.dg/pr32061.c
Modified:
    trunk/gcc/ChangeLog
    trunk/gcc/c-common.c
    trunk/gcc/c-common.h
    trunk/gcc/c-opts.c
    trunk/gcc/c-typeck.c
    trunk/gcc/c.opt
    trunk/gcc/common.opt
    trunk/gcc/cp/ChangeLog
    trunk/gcc/cp/call.c
    trunk/gcc/doc/invoke.texi
    trunk/gcc/testsuite/ChangeLog
    trunk/gcc/testsuite/g++.dg/warn/Wlogical-op-1.C
    trunk/gcc/testsuite/gcc.dg/Wlogical-op-1.c


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=32061

[Bug c/32061] (Wlogical-op) wording of warning of constant logicials need improvement

[manu at gcc dot gnu dot org]

------- Comment #7 from manu at gcc dot gnu dot org  2009-04-19 11:06 -------
FIXED in GCC 4.5


-- 

manu at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |RESOLVED
         Resolution|                            |FIXED


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=32061