[Bug c++/14710] Warning about useless casts

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* [Bug c++/14710] Warning about useless casts
       [not found] <bug-14710-4@http.gcc.gnu.org/bugzilla/>
@ 2012-03-14 10:42 ` paolo.carlini at oracle dot com
  2012-03-14 10:58 ` redi at gcc dot gnu.org
                   ` (6 subsequent siblings)
  7 siblings, 0 replies; 12+ messages in thread
From: paolo.carlini at oracle dot com @ 2012-03-14 10:42 UTC (permalink / raw)
  To: gcc-bugs

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=14710

Paolo Carlini <paolo.carlini at oracle dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |paolo.carlini at oracle dot
                   |                            |com

--- Comment #5 from Paolo Carlini <paolo.carlini at oracle dot com> 2012-03-14 10:36:10 UTC ---
Jason, what do you think about this very old request? Implementing the warning
itself should be pretty trivial (and we could have outside -Wall and -Wextra,
thus should bother no one), but I'm not sure we really want it. Then I'm not
sure where we want to draw the line, eg, in the provided snippet I'm not 100%
sure about the base class case.


^ permalink raw reply	[flat|nested] 12+ messages in thread

* [Bug c++/14710] Warning about useless casts
       [not found] <bug-14710-4@http.gcc.gnu.org/bugzilla/>
  2012-03-14 10:42 ` [Bug c++/14710] Warning about useless casts paolo.carlini at oracle dot com
@ 2012-03-14 10:58 ` redi at gcc dot gnu.org
  2012-03-14 12:54 ` paolo.carlini at oracle dot com
                   ` (5 subsequent siblings)
  7 siblings, 0 replies; 12+ messages in thread
From: redi at gcc dot gnu.org @ 2012-03-14 10:58 UTC (permalink / raw)
  To: gcc-bugs

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=14710

--- Comment #6 from Jonathan Wakely <redi at gcc dot gnu.org> 2012-03-14 10:52:18 UTC ---
I can see some value in the base class case too, but whether it's useless
depends on context, here the exact same casts are not redundant because they
select between two overloads:

struct A { int a; };
struct B : A { int b; };
void func(A *);
void func(B *);

int main()
{
    B b;

    func((A*)&b);
    func(static_cast<A*>(&b));
}


Should it apply in templates? When casting to reference types as well as
pointers? That might give a warning for std::forward and similar cases, which
are entirely correct.


^ permalink raw reply	[flat|nested] 12+ messages in thread

* [Bug c++/14710] Warning about useless casts
       [not found] <bug-14710-4@http.gcc.gnu.org/bugzilla/>
  2012-03-14 10:42 ` [Bug c++/14710] Warning about useless casts paolo.carlini at oracle dot com
  2012-03-14 10:58 ` redi at gcc dot gnu.org
@ 2012-03-14 12:54 ` paolo.carlini at oracle dot com
  2012-03-14 18:33 ` jason at gcc dot gnu.org
                   ` (4 subsequent siblings)
  7 siblings, 0 replies; 12+ messages in thread
From: paolo.carlini at oracle dot com @ 2012-03-14 12:54 UTC (permalink / raw)
  To: gcc-bugs

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=14710

--- Comment #7 from Paolo Carlini <paolo.carlini at oracle dot com> 2012-03-14 11:47:30 UTC ---
Indeed, I was vaguely considering similar things..


^ permalink raw reply	[flat|nested] 12+ messages in thread

* [Bug c++/14710] Warning about useless casts
       [not found] <bug-14710-4@http.gcc.gnu.org/bugzilla/>
                   ` (2 preceding siblings ...)
  2012-03-14 12:54 ` paolo.carlini at oracle dot com
@ 2012-03-14 18:33 ` jason at gcc dot gnu.org
  2012-03-14 23:34 ` paolo.carlini at oracle dot com
                   ` (3 subsequent siblings)
  7 siblings, 0 replies; 12+ messages in thread
From: jason at gcc dot gnu.org @ 2012-03-14 18:33 UTC (permalink / raw)
  To: gcc-bugs

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=14710

--- Comment #8 from Jason Merrill <jason at gcc dot gnu.org> 2012-03-14 18:00:33 UTC ---
I wouldn't warn about a cast that changes the type or value category of an
expression at all, or a cast that ends up being the same type as the result of
template instantiation.  But a warning for (A*)&a seems reasonable.


^ permalink raw reply	[flat|nested] 12+ messages in thread

* [Bug c++/14710] Warning about useless casts
       [not found] <bug-14710-4@http.gcc.gnu.org/bugzilla/>
                   ` (3 preceding siblings ...)
  2012-03-14 18:33 ` jason at gcc dot gnu.org
@ 2012-03-14 23:34 ` paolo.carlini at oracle dot com
  2012-03-19 15:55 ` paolo at gcc dot gnu.org
                   ` (2 subsequent siblings)
  7 siblings, 0 replies; 12+ messages in thread
From: paolo.carlini at oracle dot com @ 2012-03-14 23:34 UTC (permalink / raw)
  To: gcc-bugs

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=14710

Paolo Carlini <paolo.carlini at oracle dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |ASSIGNED
                 CC|paolo.carlini at oracle dot |
                   |com                         |
         AssignedTo|unassigned at gcc dot       |paolo.carlini at oracle dot
                   |gnu.org                     |com
   Target Milestone|---                         |4.8.0

--- Comment #9 from Paolo Carlini <paolo.carlini at oracle dot com> 2012-03-14 23:10:06 UTC ---
Ok, thanks. Let's see..


^ permalink raw reply	[flat|nested] 12+ messages in thread

* [Bug c++/14710] Warning about useless casts
       [not found] <bug-14710-4@http.gcc.gnu.org/bugzilla/>
                   ` (4 preceding siblings ...)
  2012-03-14 23:34 ` paolo.carlini at oracle dot com
@ 2012-03-19 15:55 ` paolo at gcc dot gnu.org
  2012-03-19 15:56 ` paolo.carlini at oracle dot com
  2014-02-26 21:28 ` jason at gcc dot gnu.org
  7 siblings, 0 replies; 12+ messages in thread
From: paolo at gcc dot gnu.org @ 2012-03-19 15:55 UTC (permalink / raw)
  To: gcc-bugs

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=14710

--- Comment #10 from paolo at gcc dot gnu.org <paolo at gcc dot gnu.org> 2012-03-19 15:51:36 UTC ---
Author: paolo
Date: Mon Mar 19 15:51:25 2012
New Revision: 185524

URL: http://gcc.gnu.org/viewcvs?root=gcc&view=rev&rev=185524
Log:
2012-03-16  Paolo Carlini  <paolo.carlini@oracle.com>

    PR c++/14710
    * doc/invoke.texi: Document -Wuseless-cast.

/c-family
2012-03-16  Paolo Carlini  <paolo.carlini@oracle.com>

    PR c++/14710
    * c.opt ([Wuseless-cast]): Add.

/cp
2012-03-16  Paolo Carlini  <paolo.carlini@oracle.com>

    PR c++/14710
    * cp-tree.h (maybe_warn_about_useless_cast): Declare.
    * typeck.c (maybe_warn_about_useless_cast): Define.
    (build_reinterpret_cast, build_const_cast,
    build_static_cast, cp_build_c_cast): Use it.
    * rtti.c (build_dynamic_cast): Likewise.
    * pt.c (tsubst_copy_and_build, case CAST_EXPR): Increment/decrement
    c_inhibit_evaluation_warnings before/after the build_* calls.

/testsuite
2012-03-16  Paolo Carlini  <paolo.carlini@oracle.com>

    PR c++/14710
    * g++.dg/warn/Wuseless-cast.C: New.

Added:
    trunk/gcc/testsuite/g++.dg/warn/Wuseless-cast.C
Modified:
    trunk/gcc/ChangeLog
    trunk/gcc/c-family/ChangeLog
    trunk/gcc/c-family/c.opt
    trunk/gcc/cp/ChangeLog
    trunk/gcc/cp/cp-tree.h
    trunk/gcc/cp/pt.c
    trunk/gcc/cp/rtti.c
    trunk/gcc/cp/tree.c
    trunk/gcc/cp/typeck.c
    trunk/gcc/doc/invoke.texi


^ permalink raw reply	[flat|nested] 12+ messages in thread

* [Bug c++/14710] Warning about useless casts
       [not found] <bug-14710-4@http.gcc.gnu.org/bugzilla/>
                   ` (5 preceding siblings ...)
  2012-03-19 15:55 ` paolo at gcc dot gnu.org
@ 2012-03-19 15:56 ` paolo.carlini at oracle dot com
  2014-02-26 21:28 ` jason at gcc dot gnu.org
  7 siblings, 0 replies; 12+ messages in thread
From: paolo.carlini at oracle dot com @ 2012-03-19 15:56 UTC (permalink / raw)
  To: gcc-bugs

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=14710

Paolo Carlini <paolo.carlini at oracle dot com> changed:

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

--- Comment #11 from Paolo Carlini <paolo.carlini at oracle dot com> 2012-03-19 15:54:35 UTC ---
Done.


^ permalink raw reply	[flat|nested] 12+ messages in thread

* [Bug c++/14710] Warning about useless casts
       [not found] <bug-14710-4@http.gcc.gnu.org/bugzilla/>
                   ` (6 preceding siblings ...)
  2012-03-19 15:56 ` paolo.carlini at oracle dot com
@ 2014-02-26 21:28 ` jason at gcc dot gnu.org
  7 siblings, 0 replies; 12+ messages in thread
From: jason at gcc dot gnu.org @ 2014-02-26 21:28 UTC (permalink / raw)
  To: gcc-bugs

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=14710

--- Comment #12 from Jason Merrill <jason at gcc dot gnu.org> ---
Author: jason
Date: Wed Feb 26 21:28:08 2014
New Revision: 208183

URL: http://gcc.gnu.org/viewcvs?rev=208183&root=gcc&view=rev
Log:
    PR c++/59231
    PR c++/11586
    PR c++/14710
    PR c++/57132
gcc/
    * c-common.c (shorten_compare): Don't check
    c_inhibit_evaluation_warnings.
gcc/cp/
    * pt.c (struct warning_sentinel): New.
    (tsubst_copy_and_build): Use it instead of
    c_inhibit_evaluation_warnings.

Added:
    trunk/gcc/testsuite/g++.dg/warn/Wsign-compare-7.C
Modified:
    trunk/gcc/c-family/ChangeLog
    trunk/gcc/c-family/c-common.c
    trunk/gcc/cp/ChangeLog
    trunk/gcc/cp/pt.c
    trunk/gcc/cp/typeck.c
    trunk/gcc/testsuite/g++.dg/cilk-plus/AN/array_test2_tplt.cc
    trunk/gcc/testsuite/g++.dg/cpp0x/overflow1.C


^ permalink raw reply	[flat|nested] 12+ messages in thread

* [Bug c/14710] New: Warning about useless casts
@ 2004-03-24  6:35 debian-gcc at lists dot debian dot org
  2004-03-24  6:40 ` [Bug c++/14710] " pinskia at gcc dot gnu dot org
                   ` (3 more replies)
  0 siblings, 4 replies; 12+ messages in thread
From: debian-gcc at lists dot debian dot org @ 2004-03-24  6:35 UTC (permalink / raw)
  To: gcc-bugs

[forwarded from http://bugs.debian.org/237207]

It would be nice if there was an option to add a warning about
"useless" casts. Although they are not really incorrect, they
might become incorrect/inefficient as the program evolves. Ie;

struct A { int a; };
struct B : A { int b; };
void func(A *a) { ++a; } 

int main(int ac, char **av)
{
    A a;
    B b;

    func((A*)&a); // Useless cast since a already is an A.
    func(static_cast<A*>(&a)); // Just as useless.
    func((A*)&b); // Useless cast since b is a kind of A.
    func(static_cast<A*>(&b)); // Just as useless.

    return 0;
}

-- 
           Summary: Warning about useless casts
           Product: gcc
           Version: 3.3.4
            Status: UNCONFIRMED
          Severity: enhancement
          Priority: P2
         Component: c
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: debian-gcc at lists dot debian dot org
                CC: gcc-bugs at gcc dot gnu dot org


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=14710


^ permalink raw reply	[flat|nested] 12+ messages in thread

* [Bug c++/14710] Warning about useless casts
  2004-03-24  6:35 [Bug c/14710] New: " debian-gcc at lists dot debian dot org
@ 2004-03-24  6:40 ` pinskia at gcc dot gnu dot org
  2004-03-24 16:50 ` gdr at integrable-solutions dot net
                   ` (2 subsequent siblings)
  3 siblings, 0 replies; 12+ messages in thread
From: pinskia at gcc dot gnu dot org @ 2004-03-24  6:40 UTC (permalink / raw)
  To: gcc-bugs


------- Additional Comments From pinskia at gcc dot gnu dot org  2004-03-24 06:40 -------
Confirmed, but I do not know how useful this is.

-- 
           What    |Removed                     |Added
----------------------------------------------------------------------------
          Component|c                           |c++
           Keywords|                            |diagnostic


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=14710


^ permalink raw reply	[flat|nested] 12+ messages in thread

* [Bug c++/14710] Warning about useless casts
  2004-03-24  6:35 [Bug c/14710] New: " debian-gcc at lists dot debian dot org
  2004-03-24  6:40 ` [Bug c++/14710] " pinskia at gcc dot gnu dot org
@ 2004-03-24 16:50 ` gdr at integrable-solutions dot net
  2004-03-24 16:56 ` pinskia at gcc dot gnu dot org
  2004-04-02  7:49 ` stl at caltech dot edu
  3 siblings, 0 replies; 12+ messages in thread
From: gdr at integrable-solutions dot net @ 2004-03-24 16:50 UTC (permalink / raw)
  To: gcc-bugs


------- Additional Comments From gdr at integrable-solutions dot net  2004-03-24 16:50 -------
Subject: Re:  Warning about useless casts

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

| Confirmed, but I do not know how useful this is.

Please can you make it an enhancement with low priority?

-- Gaby


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=14710


^ permalink raw reply	[flat|nested] 12+ messages in thread

* [Bug c++/14710] Warning about useless casts
  2004-03-24  6:35 [Bug c/14710] New: " debian-gcc at lists dot debian dot org
  2004-03-24  6:40 ` [Bug c++/14710] " pinskia at gcc dot gnu dot org
  2004-03-24 16:50 ` gdr at integrable-solutions dot net
@ 2004-03-24 16:56 ` pinskia at gcc dot gnu dot org
  2004-04-02  7:49 ` stl at caltech dot edu
  3 siblings, 0 replies; 12+ messages in thread
From: pinskia at gcc dot gnu dot org @ 2004-03-24 16:56 UTC (permalink / raw)
  To: gcc-bugs


------- Additional Comments From pinskia at gcc dot gnu dot org  2004-03-24 16:56 -------
Should have confirmed it.

-- 
           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |NEW
     Ever Confirmed|                            |1
           Priority|P2                          |P3
   Last reconfirmed|0000-00-00 00:00:00         |2004-03-24 16:56:18
               date|                            |


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=14710


^ permalink raw reply	[flat|nested] 12+ messages in thread

* [Bug c++/14710] Warning about useless casts
  2004-03-24  6:35 [Bug c/14710] New: " debian-gcc at lists dot debian dot org
                   ` (2 preceding siblings ...)
  2004-03-24 16:56 ` pinskia at gcc dot gnu dot org
@ 2004-04-02  7:49 ` stl at caltech dot edu
  3 siblings, 0 replies; 12+ messages in thread
From: stl at caltech dot edu @ 2004-04-02  7:49 UTC (permalink / raw)
  To: gcc-bugs


------- Additional Comments From stl at caltech dot edu  2004-04-02 07:49 -------
I am in favor of this warning, though I don't expect that it would occur often 
(except in C, where programmers incessantly cast the return values of malloc() 
and friends).

-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=14710


^ permalink raw reply	[flat|nested] 12+ messages in thread

end of thread, other threads:[~2014-02-26 21:28 UTC | newest]

Thread overview: 12+ messages (download: mbox.gz / follow: Atom feed)
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2012-03-14 10:42 ` [Bug c++/14710] Warning about useless casts paolo.carlini at oracle dot com
2012-03-14 10:58 ` redi at gcc dot gnu.org
2012-03-14 12:54 ` paolo.carlini at oracle dot com
2012-03-14 18:33 ` jason at gcc dot gnu.org
2012-03-14 23:34 ` paolo.carlini at oracle dot com
2012-03-19 15:55 ` paolo at gcc dot gnu.org
2012-03-19 15:56 ` paolo.carlini at oracle dot com
2014-02-26 21:28 ` jason at gcc dot gnu.org
2004-03-24  6:35 [Bug c/14710] New: " debian-gcc at lists dot debian dot org
2004-03-24  6:40 ` [Bug c++/14710] " pinskia at gcc dot gnu dot org
2004-03-24 16:50 ` gdr at integrable-solutions dot net
2004-03-24 16:56 ` pinskia at gcc dot gnu dot org
2004-04-02  7:49 ` stl at caltech dot edu

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