[Bug c++/34772] New: -Winit-self ignored when compiling C++ (and ObjC++)

[Bug c++/34772] New: -Winit-self ignored when compiling C++ (and ObjC++)

[olly at survex dot com]

[-- Warning: decoded text below may be mangled, UTF-8 assumed --]
[-- Attachment #1: Type: text/plain, Size: 2082 bytes --]

The info manual says:

`-Winit-self (C, C++, Objective-C and Objective-C++ only)'
     Warn about uninitialized variables which are initialized with
     themselves.  Note this option can only be used with the
     `-Wuninitialized' option, which in turn only works with `-O1' and
     above.

     For example, GCC will warn about `i' being uninitialized in the
     following snippet only when `-Winit-self' has been specified:
          int f()
          {
            int i = i;
            return i;
          }

However, trying that exact example, I get:

$ g++-4.2 -O -Wuninitialized -c warnings.cc 
warnings.cc: In function ‘int f()’:
warnings.cc:3: warning: ‘i’ is used uninitialised in this function
$ g++-4.2 -O -Wuninitialized -Wno-init-self -c warnings.cc 
warnings.cc: In function ‘int f()’:
warnings.cc:3: warning: ‘i’ is used uninitialised in this function

Compiling the same code as C:

$ gcc-4.2 -x c -O -Wuninitialized -c warnings.cc 
$ gcc-4.2 -x c -O -Wuninitialized -Winit-self -c warnings.cc
warnings.cc: In function ‘f’:
warnings.cc:3: warning: ‘i’ is used uninitialised in this function
$

So it appears that g++ simply ignores the -Winit-self setting and always warns
about such code, contrary to what the documentation states (and gcc works as
documented).  ObjC seems to handle this as C does (as documented).  ObjC++
seems to handle it as C++ does (contrary to documentation).

This could be viewed as a documentation bug, though it seems more useful for
this to work for C++ (and ObjC++) as is currently documented.

It looks like -Winit-self was new in GCC 3.4, and I can the same behaviour for
C++ with g++ 3.4.4, so I don't think this is a regression.


-- 
           Summary: -Winit-self ignored when compiling C++ (and ObjC++)
           Product: gcc
           Version: 4.2.1
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: olly at survex dot com


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=34772

[Bug c++/34772] -Winit-self ignored when compiling C++ (and ObjC++)

[olly at survex dot com]

------- Comment #1 from olly at survex dot com  2008-01-13 18:23 -------
I've just noticed that Debian have a packaged 4.3 snapshot:

g++-4.3 (Debian 4.3-20080104-1) 4.3.0 20080104 (experimental) [trunk revision
131316]

Testing with this shows the same behaviour for C++.


-- 

olly at survex dot com changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
      Known to fail|                            |3.4.4 4.2.1 4.3.0


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=34772

[Bug c++/34772] -Winit-self ignored when compiling C++ (and ObjC++)

[manu at gcc dot gnu dot org]

------- Comment #2 from manu at gcc dot gnu dot org  2008-01-14 00:42 -------
Good catch!

Well, there is something weird going on

$ cc1 -fdump-tree-original -O winit-self.c

{
  int i = i;

    int i = i;
  return i;
}

$ cc1plus -fdump-tree-original -O winit-self.c

{
  int i;

    int i;
  <<cleanup_point <<< Unknown tree: expr_stmt
  (void) (i = i) >>>
>>;
  return <retval> = i;
}


The first problem is that C++ FE does not generate a DECL_EXPR but a BIND_EXPR,
so it does not trigger the conditional in c-gimplify.c (c_gimplify_expr). My
guess is that this have never worked in C++. So we can just delete this option
from the C++ FE and convert this to an enhancement request. If none disagrees,
I will submit a patch in the next days.


-- 

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
           Keywords|                            |diagnostic
   Last reconfirmed|0000-00-00 00:00:00         |2008-01-14 00:42:56
               date|                            |


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=34772

[Bug c++/34772] -Winit-self ignored when compiling C++ (and ObjC++)

[olly at survex dot com]

------- Comment #3 from olly at survex dot com  2008-01-14 00:58 -------
If by "delete this option from the C++ FE" you mean that `g++ -Winit-self
[...]' would give an error, I'm not sure that's the best approach if the option
is likely to be sorted out for C++ in the future.  Removing it now will break
existing makefiles which use -Winit-self for C++ compilations.  And once
-Winit-self is sorted out for C++, it will be harder to write a makefile which
gives a warning for self-initialised variables for any GCC version (if it's
left as-is for now, then -Winit-self can just be specified all the time for any
GCC version >= 3.4).

The situation here is slightly odd in that -Winit-self is effectively always on
for C++, so in a way it does work - it's not specifying it (or -Wno-init-self)
which doesn't!

I think it would be better to fix the documentation to reflect the current
behaviour for C++/ObjC++, and mark this bug as an enhancement request.


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=34772

[Bug c++/34772] self-initialisation does not silence uninitialised warnings (-Winit-self ignored)

[manu at gcc dot gnu dot org]

------- Comment #4 from manu at gcc dot gnu dot org  2008-01-14 01:27 -------
(In reply to comment #3)
> I think it would be better to fix the documentation to reflect the current
> behaviour for C++/ObjC++, and mark this bug as an enhancement request.

It is a bit misleading providing -Winit-self when it has no effect and when it
cannot be disabled. But your argument about breaking existing code is solid.
So, of course, I will only update the documentation:

Index: gcc/doc/invoke.texi
===================================================================
--- gcc/doc/invoke.texi (revision 130605)
+++ gcc/doc/invoke.texi (working copy)
@@ -2827,14 +2827,15 @@
 @option{-Wnonnull} is included in @option{-Wall} and @option{-Wformat}.  It
 can be disabled with the @option{-Wno-nonnull} option.

-@item -Winit-self @r{(C, C++, Objective-C and Objective-C++ only)}
+@item -Winit-self @r{(C and Objective-C only)}
 @opindex Winit-self
 Warn about uninitialized variables which are initialized with themselves.
 Note this option can only be used with the @option{-Wuninitialized} option,
 which in turn only works with @option{-O1} and above.

-For example, GCC will warn about @code{i} being uninitialized in the
-following snippet only when @option{-Winit-self} has been specified:
+For C and Objective-C, GCC will silence the warning about @code{i}
+being uninitialized in the following snippet unless
+@option{-Winit-self} has been specified:
 @smallexample
 @group
 int f()
@@ -3094,11 +3095,12 @@
 These warnings are possible only in optimizing compilation,
 because they require data flow information that is computed only
 when optimizing.  If you do not specify @option{-O}, you will not get
-these warnings. Instead, GCC will issue a warning about
@option{-Wuninitialized}
-requiring @option{-O}.
+these warnings. Instead, GCC will issue a warning about
+@option{-Wuninitialized} requiring @option{-O}.

-If you want to warn about code which uses the uninitialized value of the
-variable in its own initializer, use the @option{-Winit-self} option.
+For C and Objective-C, using the uninitialized value of the variable in its
+own initializer (e.g. @samp{int i = i;}) silences the warning. If you
+want to warn about such code use the @option{-Winit-self} option.

 These warnings occur for individual uninitialized or clobbered
 elements of structure, union or array variables as well as for


-- 

manu at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Severity|normal                      |enhancement
            Summary|-Winit-self ignored when    |self-initialisation does not
                   |compiling C++ (and ObjC++)  |silence uninitialised
                   |                            |warnings (-Winit-self
                   |                            |ignored)


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=34772

[Bug c++/34772] self-initialisation does not silence uninitialised warnings (-Winit-self ignored)

[manu at gcc dot gnu dot org]

------- Comment #5 from manu at gcc dot gnu dot org  2008-01-14 01:35 -------
Actually. Winit-self was introduced in GCC 3.4 but the init-self trick was
probably introduced earlier. So this may actually be a regression from much
earlier. Anyway, documenting that it doesn't work seems the right thing to do.


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=34772

[Bug c++/34772] self-initialisation does not silence uninitialised warnings (-Winit-self ignored)

[pinskia at gcc dot gnu dot org]

------- Comment #6 from pinskia at gcc dot gnu dot org  2008-01-14 01:45 -------
This should work, if it does not then it is a bug.


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=34772

[Bug c++/34772] [3.4/4.0/4.1/4.2/4.3 Regression] self-initialisation does not silence uninitialised warnings (-Winit-self ignored)

[manu at gcc dot gnu dot org]

------- Comment #7 from manu at gcc dot gnu dot org  2008-01-14 02:08 -------
So it seems this worked in 3.3, so it is a regression after all.


-- 

manu at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Severity|enhancement                 |normal
            Summary|self-initialisation does not|[3.4/4.0/4.1/4.2/4.3
                   |silence uninitialised       |Regression] self-
                   |warnings (-Winit-self       |initialisation does not
                   |ignored)                    |silence uninitialised
                   |                            |warnings (-Winit-self
                   |                            |ignored)


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=34772

[Bug c++/34772] [4.1/4.2/4.3 Regression] self-initialisation does not silence uninitialised warnings (-Winit-self ignored)

[rguenth at gcc dot gnu dot org]

------- Comment #8 from rguenth at gcc dot gnu dot org  2008-01-14 10:46 -------
Regression for a GCC extension that silences a diagnostic.  P4.


-- 

rguenth at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
      Known to work|                            |3.3.6
           Priority|P3                          |P4
            Summary|[3.4/4.0/4.1/4.2/4.3        |[4.1/4.2/4.3 Regression]
                   |Regression] self-           |self-initialisation does not
                   |initialisation does not     |silence uninitialised
                   |silence uninitialised       |warnings (-Winit-self
                   |warnings (-Winit-self       |ignored)
                   |ignored)                    |
   Target Milestone|---                         |4.1.3


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=34772

[Bug c++/34772] [4.1/4.2/4.3 Regression] self-initialisation does not silence uninitialised warnings (-Winit-self ignored)

[pinskia at gcc dot gnu dot org]

------- Comment #9 from pinskia at gcc dot gnu dot org  2008-01-20 05:39 -------
Tomorrow after my extra checking build finishes, I will look into fixing this
bug.


-- 

pinskia at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |pinskia at gcc dot gnu dot
                   |                            |org


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=34772

[Bug c++/34772] [4.2/4.3/4.4 Regression] self-initialisation does not silence uninitialised warnings (-Winit-self ignored)

[jsm28 at gcc dot gnu dot org]

------- Comment #10 from jsm28 at gcc dot gnu dot org  2008-07-04 22:28 -------
Closing 4.1 branch.


-- 

jsm28 at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
            Summary|[4.1/4.2/4.3/4.4 Regression]|[4.2/4.3/4.4 Regression]
                   |self-initialisation does not|self-initialisation does not
                   |silence uninitialised       |silence uninitialised
                   |warnings (-Winit-self       |warnings (-Winit-self
                   |ignored)                    |ignored)
   Target Milestone|4.1.3                       |4.2.5


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=34772

[Bug c++/34772] [4.2/4.3/4.4 Regression] self-initialisation does not silence uninitialised warnings (-Winit-self ignored)

[paolo dot carlini at oracle dot com]

------- Comment #11 from paolo dot carlini at oracle dot com  2008-10-16 16:16 -------
*** Bug 37854 has been marked as a duplicate of this bug. ***


-- 

paolo dot carlini at oracle dot com changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |julien dot sagnard at gmail
                   |                            |dot com


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=34772

[Bug c++/34772] [4.3/4.4/4.5 Regression] self-initialisation does not silence uninitialised warnings (-Winit-self ignored)

[jsm28 at gcc dot gnu dot org]

------- Comment #12 from jsm28 at gcc dot gnu dot org  2009-03-31 20:17 -------
Closing 4.2 branch.


-- 

jsm28 at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
            Summary|[4.2/4.3/4.4/4.5 Regression]|[4.3/4.4/4.5 Regression]
                   |self-initialisation does not|self-initialisation does not
                   |silence uninitialised       |silence uninitialised
                   |warnings (-Winit-self       |warnings (-Winit-self
                   |ignored)                    |ignored)
   Target Milestone|4.2.5                       |4.3.4


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=34772

[Bug c++/34772] [4.3/4.4/4.5 Regression] self-initialisation does not silence uninitialised warnings (-Winit-self ignored)

[rguenth at gcc dot gnu dot org]

------- Comment #13 from rguenth at gcc dot gnu dot org  2009-08-04 12:28 -------
GCC 4.3.4 is being released, adjusting target milestone.


-- 

rguenth at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Target Milestone|4.3.4                       |4.3.5


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=34772

[Bug c++/34772] [4.3/4.4/4.5 Regression] self-initialisation does not silence uninitialised warnings (-Winit-self ignored)

[manu at gcc dot gnu dot org]

------- Comment #14 from manu at gcc dot gnu dot org  2009-12-30 11:29 -------
*** Bug 42238 has been marked as a duplicate of this bug. ***


-- 

manu at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |ext at sidvind dot com


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=34772

[Bug c++/34772] [4.3/4.4/4.5/4.6 Regression] self-initialisation does not silence uninitialised warnings (-Winit-self ignored)

[rguenth at gcc dot gnu dot org]

------- Comment #15 from rguenth at gcc dot gnu dot org  2010-05-22 18:11 -------
GCC 4.3.5 is being released, adjusting target milestone.


-- 

rguenth at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Target Milestone|4.3.5                       |4.3.6


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=34772