[Bug c/24900] New: new "value computed is not used" warning in gcc 4.1

[Bug c/24900] New: new "value computed is not used" warning in gcc 4.1

[arjanv at redhat dot com]

attached testcase gives a "value computed is not used" warning.
Testcase comes from the linux kernel which spews this for every .c file
compiled


-- 
           Summary: new "value computed is not used" warning in gcc 4.1
           Product: gcc
           Version: 4.1.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: arjanv at redhat dot com
  GCC host triplet: x86_64-unknown-linux-gnu


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=24900

[Bug c/24900] new "value computed is not used" warning in gcc 4.1

[arjanv at redhat dot com]

------- Comment #1 from arjanv at redhat dot com  2005-11-16 18:21 -------
Created an attachment (id=10257)
 --> (http://gcc.gnu.org/bugzilla/attachment.cgi?id=10257&action=view)
fairly minimal testcase


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=24900

[Bug c/24900] new "value computed is not used" warning in gcc 4.1

[arjanv at redhat dot com]

------- Comment #2 from arjanv at redhat dot com  2005-11-16 18:23 -------
(compiler flags used were -O2 -Wall)


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=24900

[Bug c/24900] new "value computed is not used" warning in gcc 4.1

[pinskia at gcc dot gnu dot org]

------- Comment #3 from pinskia at gcc dot gnu dot org  2005-11-16 18:30 -------
Here is a further reduced testcase:
unsigned long t(void);

void apic_write_atomic(unsigned long reg, unsigned int v)
{
 ((__typeof__(*((volatile unsigned int *)((t())+reg))))t());
}

-Wall is all is needed to reproduce the issue.


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=24900

[Bug c/24900] [4.1 Regression] new "value computed is not used" warning in gcc 4.1

[pinskia at gcc dot gnu dot org]

-- 

pinskia at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
      Known to fail|                            |4.1.0
      Known to work|                            |4.0.3
            Summary|new "value computed is not  |[4.1 Regression] new "value
                   |used" warning in gcc 4.1    |computed is not used"
                   |                            |warning in gcc 4.1
   Target Milestone|---                         |4.1.0


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=24900

[Bug c/24900] [4.1 Regression] new "value computed is not used" warning in gcc 4.1

[pinskia at gcc dot gnu dot org]

------- Comment #4 from pinskia at gcc dot gnu dot org  2005-11-16 18:36 -------
Reduces down to:
int f(void);
void g(void)
{
  (unsigned) f();
}

The typeof gets changed over to unsigned.

Maybe this is not a bug after all.  Can someone else comment on this?


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=24900

[Bug middle-end/24900] [4.1 Regression] new "value computed is not used" warning in gcc 4.1

[pinskia at gcc dot gnu dot org]

------- Comment #5 from pinskia at gcc dot gnu dot org  2005-11-16 18:45 -------
Confirmed, this comes from a macro expansion, we really should not warn about
this.

The bug is in stmt.c.


-- 

pinskia at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |NEW
          Component|c                           |middle-end
     Ever Confirmed|0                           |1
   Last reconfirmed|0000-00-00 00:00:00         |2005-11-16 18:45:47
               date|                            |


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=24900

[Bug middle-end/24900] [4.1 Regression] new "value computed is not used" warning in gcc 4.1

[aldyh at gcc dot gnu dot org]

------- Comment #6 from aldyh at gcc dot gnu dot org  2005-11-16 20:10 -------
I'll take a look at this.


-- 

aldyh at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
         AssignedTo|unassigned at gcc dot gnu   |aldyh at gcc dot gnu dot org
                   |dot org                     |
             Status|NEW                         |ASSIGNED


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=24900

[Bug middle-end/24900] [4.1 Regression] new "value computed is not used" warning in gcc 4.1

[aldyh at gcc dot gnu dot org]

------- Comment #7 from aldyh at gcc dot gnu dot org  2005-11-17 21:12 -------
We used to allow this, but have now made the warning stricter.  This behavior
was done deliberately.  See:

http://gcc.gnu.org/ml/gcc-patches/2005-08/msg00275.html

As is explained in the thread, you can modify the macro to use statement
expressions and avoid the warning.


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=24900

[Bug middle-end/24900] [4.1 Regression] new "value computed is not used" warning in gcc 4.1

[aldyh at gcc dot gnu dot org]

------- Comment #8 from aldyh at gcc dot gnu dot org  2005-11-17 21:15 -------
See previous comment.


-- 

aldyh at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|ASSIGNED                    |RESOLVED
         Resolution|                            |WONTFIX


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=24900

[Bug middle-end/24900] [4.1 Regression] new "value computed is not used" warning in gcc 4.1

[pinskia at gcc dot gnu dot org]

------- Comment #9 from pinskia at gcc dot gnu dot org  2006-01-16 15:30 -------
*** Bug 25810 has been marked as a duplicate of this bug. ***


-- 

pinskia at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |wingo at pobox dot com


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=24900

[Bug middle-end/24900] [4.1 Regression] new "value computed is not used" warning in gcc 4.1

[pinskia at gcc dot gnu dot org]

------- Comment #10 from pinskia at gcc dot gnu dot org  2006-01-25 13:06 -------
*** Bug 25955 has been marked as a duplicate of this bug. ***


-- 

pinskia at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |mike at codeweavers dot com


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=24900

[Bug middle-end/24900] [4.1 Regression] new "value computed is not used" warning in gcc 4.1

[mike at codeweavers dot com]

------- Comment #11 from mike at codeweavers dot com  2006-01-26 03:02 -------
Unfortunately statement expressions don't look like portable C.
The (windowsx.h) macros we use in Wine are Windows macros and can't be changed.
To get rid of these warnings it's likely we'll have to turn off the computed
value not used warning, which used to show some useful warnings...


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=24900