[Bug c/26632] New: spurious warning: value computed is not used

[Bug c/26632] New: spurious warning: value computed is not used

[mattias at virtutech dot se]

Using gcc 4.1.0 on amd64, with -Wall (64 bit target):

int g(void);
long h(void);
void f(void)
{
        0 ? h() : g();
}

foo.c:6: warning: value computed is not used

Either changing 0 to 1 or swapping g and h makes the warning go away.
This was the result of a (very reasonable) macro expansion.


-- 
           Summary: spurious warning: value computed is not used
           Product: gcc
           Version: 4.1.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: mattias at virtutech dot se
 GCC build triplet: x86_64-unknown-linux-gnu
  GCC host triplet: x86_64-unknown-linux-gnu
GCC target triplet: x86_64-unknown-linux-gnu


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=26632

[Bug middle-end/26632] [4.1/4.2 Regression] spurious warning: value computed is not used

[pinskia at gcc dot gnu dot org]

------- Comment #2 from pinskia at gcc dot gnu dot org  2006-03-10 15:17 -------
I don't know if we should be warning or not.


-- 

pinskia at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |pinskia at gcc dot gnu dot
                   |                            |org
           Keywords|                            |diagnostic
            Summary|spurious warning: value     |[4.1/4.2 Regression]
                   |computed is not used        |spurious warning: value
                   |                            |computed is not used
   Target Milestone|---                         |4.1.1


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=26632

[Bug middle-end/26632] spurious warning: value computed is not used

[pinskia at gcc dot gnu dot org]

------- Comment #1 from pinskia at gcc dot gnu dot org  2006-03-10 15:16 -------
Hmm, what is going on here is the following.
        0 ? h() : g();
is not really just that but instead:
        0 ? h() : (long)g();
which then gets foldded into:
(long)g();
and we warn about the cast.


-- 

pinskia at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
          Component|c                           |middle-end


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=26632

[Bug middle-end/26632] [4.1/4.2 Regression] spurious warning: value computed is not used

[mattias at virtutech dot se]

------- Comment #3 from mattias at virtutech dot se  2006-03-10 15:30 -------
Yes, I realise it's the implicit integral conversion that causes the warning,
but since the result is not used no matter what it seems wrong to warn for it -
it cannot reasonably a sign of an error in the code.

It can be hard to avoid unless the exact types and sizes are known - for
instance, adding (long) casts to both branches will not prevent the warning
from being generated. This causes headaches with -Werror.

In fact, adding an (int) cast before h() will suppress the warning but a (long)
cast before g() will not. I see no sensible way of getting rid of the warning
at all, save casting the whole result to void (which isn't desirable for a
function-like macro).


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=26632

[Bug middle-end/26632] [4.1/4.2 Regression] spurious warning: value computed is not used

[neil at daikokuya dot co dot uk]

------- Comment #4 from neil at daikokuya dot co dot uk  2006-03-11 00:15 -------
Subject: Re:  spurious warning: value computed is not used

pinskia at gcc dot gnu dot org wrote:-

> 
> 
> ------- Comment #1 from pinskia at gcc dot gnu dot org  2006-03-10 15:16 -------
> Hmm, what is going on here is the following.
>         0 ? h() : g();
> is not really just that but instead:
>         0 ? h() : (long)g();
> which then gets foldded into:
> (long)g();
> and we warn about the cast.

Every time we get bitten by issuing diagnostics after parts of GCC
other than the front end manipulate the IR.  These bugs won't go
away until GCC stops doing this.

Neil.


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=26632

[Bug middle-end/26632] [4.1/4.2 Regression] spurious warning: value computed is not used

[mmitchel at gcc dot gnu dot org]

------- Comment #5 from mmitchel at gcc dot gnu dot org  2006-04-16 18:58 -------
I am glad that Neil agrees my oft-stated, but always-rejected, claim that only
the front ends should issue warnings.  :-)

However, in this case, we can presumably fix the bug by setting TREE_NO_WARNING
on the cast expression, which, one hopes, is generated by the front end.

In any case, this is definitely a bug. 


-- 

mmitchel at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Priority|P3                          |P2


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=26632

[Bug middle-end/26632] [4.1/4.2 Regression] spurious warning: value computed is not used

[mmitchel at gcc dot gnu dot org]

------- Comment #6 from mmitchel at gcc dot gnu dot org  2006-05-25 02:34 -------
Will not be fixed in 4.1.1; adjust target milestone to 4.1.2.


-- 

mmitchel at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Target Milestone|4.1.1                       |4.1.2


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=26632

[Bug middle-end/26632] [4.1/4.2 Regression] spurious warning: value computed is not used

[pinskia at gcc dot gnu dot org]

------- Comment #7 from pinskia at gcc dot gnu dot org  2006-05-30 13:54 -------
*** Bug 27825 has been marked as a duplicate of this bug. ***


-- 

pinskia at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |ebermann at decomsys dot com


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=26632

[Bug middle-end/26632] [4.1/4.2 Regression] spurious warning: value computed is not used

[pinskia at gcc dot gnu dot org]

------- Comment #8 from pinskia at gcc dot gnu dot org  2006-06-30 06:07 -------
Confirmed.


-- 

pinskia at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |NEW
     Ever Confirmed|0                           |1
   Last reconfirmed|0000-00-00 00:00:00         |2006-06-30 06:07:10
               date|                            |


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=26632

[Bug middle-end/26632] [4.1/4.2 Regression] spurious warning: value computed is not used

[pinskia at gcc dot gnu dot org]

-- 

pinskia at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
         AssignedTo|unassigned at gcc dot gnu   |kazu at gcc dot gnu dot org
                   |dot org                     |
                URL|                            |http://gcc.gnu.org/ml/gcc-
                   |                            |patches/2006-
                   |                            |08/msg01041.html
             Status|NEW                         |ASSIGNED
  GCC build triplet|x86_64-unknown-linux-gnu    |
   GCC host triplet|x86_64-unknown-linux-gnu    |
 GCC target triplet|x86_64-unknown-linux-gnu    |
           Keywords|                            |patch


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=26632

[Bug middle-end/26632] [4.1/4.2 Regression] spurious warning: value computed is not used

[kazu at gcc dot gnu dot org]

------- Comment #9 from kazu at gcc dot gnu dot org  2006-08-28 17:18 -------
Subject: Bug 26632

Author: kazu
Date: Mon Aug 28 17:18:29 2006
New Revision: 116510

URL: http://gcc.gnu.org/viewcvs?root=gcc&view=rev&rev=116510
Log:
gcc/
        PR middle-end/26632
        * convert.c (convert_to_integer): Set TREE_NO_WARNING to 1 on
        an implicit conversion.

gcc/testsuite/
        PR middle-end/26632
        * gcc.dg/pr26632.c: New.

Modified:
    trunk/gcc/ChangeLog
    trunk/gcc/convert.c
    trunk/gcc/testsuite/ChangeLog


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=26632

[Bug middle-end/26632] [4.1 Regression] spurious warning: value computed is not used

[kazu at gcc dot gnu dot org]

------- Comment #10 from kazu at gcc dot gnu dot org  2006-08-30 06:00 -------
Subject: Bug 26632

Author: kazu
Date: Wed Aug 30 06:00:35 2006
New Revision: 116580

URL: http://gcc.gnu.org/viewcvs?root=gcc&view=rev&rev=116580
Log:
        PR middle-end/26632
        * gcc.dg/pr26632.c: New.

Added:
    trunk/gcc/testsuite/gcc.dg/pr26632.c


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=26632

[Bug middle-end/26632] [4.1 Regression] spurious warning: value computed is not used

[mmitchel at gcc dot gnu dot org]

-- 

mmitchel at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Target Milestone|4.1.2                       |4.1.3


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=26632

[Bug middle-end/26632] [4.1 Regression] spurious warning: value computed is not used

[jsm28 at gcc dot gnu dot org]

------- Comment #11 from jsm28 at gcc dot gnu dot org  2008-07-04 15:23 -------
Closing 4.1 branch.


-- 

jsm28 at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|ASSIGNED                    |RESOLVED
      Known to fail|                            |4.1.3
      Known to work|                            |4.2.0
         Resolution|                            |FIXED
   Target Milestone|4.1.3                       |4.2.0


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=26632