[Bug c++/11224] New: [regression] warning "value computed is not used" no longer emitted

[Bug c++/11224] New: [regression] warning "value computed is not used" no longer emitted

[mueller@kde.org]

PLEASE REPLY TO gcc-bugzilla@gcc.gnu.org ONLY, *NOT* gcc-bugs@gcc.gnu.org.

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=11224

           Summary: [regression] warning "value computed is not used" no
                    longer emitted
           Product: gcc
           Version: unknown
            Status: UNCONFIRMED
          Severity: normal
          Priority: P2
         Component: c++
        AssignedTo: unassigned@gcc.gnu.org
        ReportedBy: mueller@kde.org
                CC: gcc-bugs@gcc.gnu.org
 GCC build triplet: i486-suse-linux-gnu
  GCC host triplet: i486-suse-linux-gnu
GCC target triplet: i486-suse-linux-gnu

Hi,  
 
the attached testcase does no longer emit the "value computed is not 
used" warning. The regression was introduced somewhere between 2.95.4 and 
gcc 3.0.4, I'm currently trying to find the commit that broke it.  
 
I compile with g++ -Wall -W -O2 -c unused.cc 
 
expected output: 
 
unused.cc: In function `int main()': 
unused.cc:12: warning: value computed is not used 
 
actual output: <nothing>

[Bug c++/11224] [regression] warning "value computed is not used" no longer emitted

[mueller@kde.org]

PLEASE REPLY TO gcc-bugzilla@gcc.gnu.org ONLY, *NOT* gcc-bugs@gcc.gnu.org.

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=11224



------- Additional Comments From mueller@kde.org  2003-06-17 17:56 -------
Created an attachment (id=4236)
 --> (http://gcc.gnu.org/bugzilla/attachment.cgi?id=4236&action=view)
testcase showing the problem.

[Bug c++/11224] [3.3/3.4 regression] warning "value computed is not used" no longer emitted

[pinskia@physics.uc.edu]

PLEASE REPLY TO gcc-bugzilla@gcc.gnu.org ONLY, *NOT* gcc-bugs@gcc.gnu.org.

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=11224


pinskia@physics.uc.edu changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |NEW
     Ever Confirmed|                            |1
   Last reconfirmed|0000-00-00 00:00:00         |2003-06-17 18:12:14
               date|                            |
            Summary|[regression] warning "value |[3.3/3.4 regression] warning
                   |computed is not used" no    |"value computed is not used"
                   |longer emitted              |no longer emitted
   Target Milestone|3.4                         |3.3.1
            Version|unknown                     |3.0.4


------- Additional Comments From pinskia@physics.uc.edu  2003-06-17 18:12 -------
I can confirm this on the mainline (20030617), I think the problem is that isEmpty is not really 
being marked const so gcc says that there could be some side-effects which is clearly not true. 

from stmt.c:2430:
/* If this is an expression with side effects, don't warn.  */
      if (TREE_SIDE_EFFECTS (exp))
        return 0;

[Bug c++/11224] [3.3/3.4 regression] warning "value computed is not used" no longer emitted

[dhazeghi@yahoo.com]

PLEASE REPLY TO gcc-bugzilla@gcc.gnu.org ONLY, *NOT* gcc-bugs@gcc.gnu.org.

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=11224



------- Additional Comments From dhazeghi@yahoo.com  2003-06-17 18:26 -------
Note that RedHat's patched 2.96 warns correctly while 3.0 does not.

[Bug c++/11224] [3.3/3.4 regression] warning "value computed is not used" no longer emitted

[mueller at kde dot org]

PLEASE REPLY TO gcc-bugzilla@gcc.gnu.org ONLY, *NOT* gcc-bugs@gcc.gnu.org.

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=11224



------- Additional Comments From mueller at kde dot org  2003-06-18 18:26 -------
adding __attribute__ ((pure)) or __attribute__ ((const)) makes no difference.  
 
however, its indeed caused by the HAS_SIDEEFFECTS check, as further checking 
has confirmed.

[Bug c++/11224] [3.3/3.4 regression] warning "value computed is not used" no longer emitted

[mmitchel at gcc dot gnu dot org]

PLEASE REPLY TO gcc-bugzilla@gcc.gnu.org ONLY, *NOT* gcc-bugs@gcc.gnu.org.

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=11224


mmitchel at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Target Milestone|3.3.1                       |3.4


------- Additional Comments From mmitchel at gcc dot gnu dot org  2003-06-27 21:45 -------
This defect cannot easily be fixed.

The key problem is that TREE_SIDE_EFFECTS isn't the right test; the "x == foo()"
expression has side-effects, but that doesn't mean that the result of the
comparison is being used.

Distinguishing that case from "foo()" itself can't be done with
TREE_SIDE_EFFECTS; we need to look at the actual expression itself.

I've retargeted this PR for 3.4.

[Bug c++/11224] [3.3/3.4 regression] warning "value computed is not used" no longer emitted

[nathan at gcc dot gnu dot org]

PLEASE REPLY TO gcc-bugzilla@gcc.gnu.org ONLY, *NOT* gcc-bugs@gcc.gnu.org.

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=11224


nathan at gcc dot gnu dot org changed:

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


------- Additional Comments From nathan at gcc dot gnu dot org  2003-09-06 19:39 -------
add more smarts to convert_to_void so that it looks at the outermost tree code
to figure if that causes sideeffects

[Bug c++/11224] [3.3/3.4 regression] warning "value computed is not used" no longer emitted

[pinskia at gcc dot gnu dot org]

-- 
           What    |Removed                     |Added
----------------------------------------------------------------------------
           Severity|normal                      |minor


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=11224

[Bug c++/11224] [3.3/3.4 regression] warning "value computed is not used" no longer emitted

[pinskia at gcc dot gnu dot org]

------- Additional Comments From pinskia at gcc dot gnu dot org  2004-01-10 23:22 -------
This is regression from 2.95.3 so moving to 3.4.1 and this should not block the branching.

-- 
           What    |Removed                     |Added
----------------------------------------------------------------------------
   Target Milestone|3.4.0                       |3.4.1


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=11224

[Bug c++/11224] [3.3/3.4 regression] warning "value computed is not used" no longer emitted

[steven at gcc dot gnu dot org]

------- Additional Comments From steven at gcc dot gnu dot org  2004-01-12 23:39 -------
Move back the target for all regressions from 3.4.1 to 3.4.0, as required by 
our bug management policy. 

-- 
           What    |Removed                     |Added
----------------------------------------------------------------------------
   Target Milestone|3.4.1                       |3.4.0


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=11224

[Bug c++/11224] [3.3/3.4/3.5 regression] warning "value computed is not used" no longer emitted

[mmitchel at gcc dot gnu dot org]

------- Additional Comments From mmitchel at gcc dot gnu dot org  2004-02-20 09:09 -------
Postponing until 3.5; any fix will be more dangerous than useful for 3.4.x.

-- 
           What    |Removed                     |Added
----------------------------------------------------------------------------
   Target Milestone|3.4.0                       |3.5.0


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=11224

[Bug c++/11224] [3.3/3.4/4.0 regression] warning "value computed is not used" no longer emitted

[nathan at gcc dot gnu dot org]

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


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=11224

[Bug c++/11224] [3.3/3.4/4.0 regression] warning "value computed is not used" no longer emitted

[mmitchel at gcc dot gnu dot org]

------- Additional Comments From mmitchel at gcc dot gnu dot org  2004-12-22 04:57 -------
Working on a fix.

-- 
           What    |Removed                     |Added
----------------------------------------------------------------------------
         AssignedTo|unassigned at gcc dot gnu   |mark at codesourcery dot com
                   |dot org                     |
             Status|NEW                         |ASSIGNED


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=11224

[Bug c++/11224] [3.3/3.4/4.0 regression] warning "value computed is not used" no longer emitted

[cvs-commit at gcc dot gnu dot org]

------- Additional Comments From cvs-commit at gcc dot gnu dot org  2004-12-22 18:01 -------
Subject: Bug 11224

CVSROOT:	/cvs/gcc
Module name:	gcc
Changes by:	mmitchel@gcc.gnu.org	2004-12-22 18:00:41

Modified files:
	gcc/testsuite  : ChangeLog 
	gcc/cp         : ChangeLog call.c cp-gimplify.c cvt.c rtti.c 
	                 typeck.c 
Added files:
	gcc/testsuite/g++.dg/template: cond5.C 
	gcc/testsuite/g++.dg/inherit: thunk3.C 
	gcc/testsuite/g++.dg/warn: Wunused-9.C 

Log message:
	PR c++/18464
	* call.c (build_this): In templates, do not bother with
	build_unary_op.
	* typeck.c (unary_complex_lvalue): In a template, always refuse
	simplifications.
	
	PR c++/18492
	* cp-gimplify.c (cp_genericize): Relax assertion.
	
	PR c++/11224
	* cvt.c (convert_to_void): Warn about unused values.
	
	PR c++/18257
	* rtti.c (emit_support_tinfos): On systems without weak symbols,
	emit the runtime library type-info objects as non-COMDAT.
	
	PR c++/18464
	* g++.dg/template/cond5.C: New test.
	
	PR c++/18492
	* g++.dg/inherit/thunk3.C: New test.
	
	PR c++/11224
	* g++.dg/warn/Wunused-9.C: New test.

Patches:
http://gcc.gnu.org/cgi-bin/cvsweb.cgi/gcc/gcc/testsuite/ChangeLog.diff?cvsroot=gcc&r1=1.4799&r2=1.4800
http://gcc.gnu.org/cgi-bin/cvsweb.cgi/gcc/gcc/testsuite/g++.dg/template/cond5.C.diff?cvsroot=gcc&r1=NONE&r2=1.1
http://gcc.gnu.org/cgi-bin/cvsweb.cgi/gcc/gcc/testsuite/g++.dg/inherit/thunk3.C.diff?cvsroot=gcc&r1=NONE&r2=1.1
http://gcc.gnu.org/cgi-bin/cvsweb.cgi/gcc/gcc/testsuite/g++.dg/warn/Wunused-9.C.diff?cvsroot=gcc&r1=NONE&r2=1.1
http://gcc.gnu.org/cgi-bin/cvsweb.cgi/gcc/gcc/cp/ChangeLog.diff?cvsroot=gcc&r1=1.4551&r2=1.4552
http://gcc.gnu.org/cgi-bin/cvsweb.cgi/gcc/gcc/cp/call.c.diff?cvsroot=gcc&r1=1.524&r2=1.525
http://gcc.gnu.org/cgi-bin/cvsweb.cgi/gcc/gcc/cp/cp-gimplify.c.diff?cvsroot=gcc&r1=1.16&r2=1.17
http://gcc.gnu.org/cgi-bin/cvsweb.cgi/gcc/gcc/cp/cvt.c.diff?cvsroot=gcc&r1=1.174&r2=1.175
http://gcc.gnu.org/cgi-bin/cvsweb.cgi/gcc/gcc/cp/rtti.c.diff?cvsroot=gcc&r1=1.205&r2=1.206
http://gcc.gnu.org/cgi-bin/cvsweb.cgi/gcc/gcc/cp/typeck.c.diff?cvsroot=gcc&r1=1.605&r2=1.606



-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=11224

[Bug c++/11224] [3.3/3.4 regression] warning "value computed is not used" no longer emitted

[mmitchel at gcc dot gnu dot org]

------- Additional Comments From mmitchel at gcc dot gnu dot org  2004-12-22 18:06 -------
Fixed in G++ 4.0.

-- 
           What    |Removed                     |Added
----------------------------------------------------------------------------
            Summary|[3.3/3.4/4.0 regression]    |[3.3/3.4 regression] warning
                   |warning "value computed is  |"value computed is not used"
                   |not used" no longer emitted |no longer emitted


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=11224

[Bug c++/11224] [3.3/3.4 regression] warning "value computed is not used" no longer emitted

[jgrimm2 at us dot ibm dot com]

------- Additional Comments From jgrimm2 at us dot ibm dot com  2005-01-10 19:01 -------

FWIW, the xfail on Wunused-9.C :

...
  +f(); // { dg-warning "not used" "" { xfail *-*-* } }
...

is no longer failing, per: 

http://gcc.gnu.org/ml/gcc-testresults/2004-12/msg01344.html
http://gcc.gnu.org/ml/gcc-testresults/2004-12/msg01354.html

no longer an xfail?

-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=11224

[Bug c++/11224] [3.3/3.4 regression] warning "value computed is not used" no longer emitted

[pinskia at gcc dot gnu dot org]

-- 
           What    |Removed                     |Added
----------------------------------------------------------------------------
   Target Milestone|4.0.0                       |3.4.4


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=11224

[Bug c++/11224] [3.3/3.4 regression] warning "value computed is not used" no longer emitted

[mmitchel at gcc dot gnu dot org]

-- 
           What    |Removed                     |Added
----------------------------------------------------------------------------
   Target Milestone|3.4.4                       |3.4.5


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=11224