[Bug c++/25314] New: Unreachable code at beginning of switch statement is not reported anymore

[Bug c++/25314] New: Unreachable code at beginning of switch statement is not reported anymore

[Uwe dot Seimet at seimet dot de]

The warning available in previous versions of gcc (at least until gcc 3.3)
'unreachable code at beginning of switch statement' is not reported anymore.
This behavior hides programming errors. When compiling this code sample with
'c++ -Wall test.cpp':

int main()
{
        int a;

        switch(1)
        {
                a = 1;
                break;

                default:
                break;
        }

        return 0;
}

No warning is reported. Older versions of gcc issue a warning here. Using
additional switch-related warnings like -Wswitch does not change anything.


-- 
           Summary: Unreachable code at beginning of switch statement is not
                    reported anymore
           Product: gcc
           Version: 4.0.2
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: Uwe dot Seimet at seimet dot de
 GCC build triplet: i686-pc-linux-gnu
  GCC host triplet: i686-pc-linux-gnu
GCC target triplet: i686-pc-linux-gnu


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=25314

[Bug c/25314] [3.4/4.0/4.1/4.2 Regression] Unreachable code at beginning of switch statement is not reported anymore

[pinskia at gcc dot gnu dot org]

------- Comment #1 from pinskia at gcc dot gnu dot org  2005-12-08 18:32 -------
Hmm, someone else has to do decide if we only want to warn about this with
-Wunreachable-code or with just -W -Wall because 3.4.0 and above only warn with
-Wunreachable-code.


-- 

pinskia at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
          Component|c++                         |c
           Keywords|                            |diagnostic
            Summary|Unreachable code at         |[3.4/4.0/4.1/4.2 Regression]
                   |beginning of switch         |Unreachable code at
                   |statement is not reported   |beginning of switch
                   |anymore                     |statement is not reported
                   |                            |anymore
   Target Milestone|---                         |4.0.3


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=25314

[Bug c/25314] [3.4/4.0/4.1/4.2 Regression] Unreachable code at beginning of switch statement is not reported anymore

[Uwe dot Seimet at seimet dot de]

------- Comment #2 from Uwe dot Seimet at seimet dot de  2005-12-08 18:37 -------
Subject: Re:  [3.4/4.0/4.1/4.2 Regression] Unreachable code at beginning of
switch statement is not reported anymore

Hello,

> Hmm, someone else has to do decide if we only want to warn about this with
> -Wunreachable-code or with just -W -Wall because 3.4.0 and above only warn with
> -Wunreachable-code.

Thank you for your quick response! It was not obvious for me that
-Wunreachable-code would enable the correct warning, since in previous
versions this warning was covered by -Wall.
It would be nice for -Wall to include -Wunreachable-code, similar to how
it was in gcc 3.3.

Best regards,  Uwe


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=25314

[Bug c/25314] [3.4/4.0/4.1/4.2 Regression] Unreachable code at beginning of switch statement is not reported anymore

[pinskia at gcc dot gnu dot org]

------- Comment #3 from pinskia at gcc dot gnu dot org  2005-12-08 18:59 -------
(In reply to comment #2)
> It would be nice for -Wall to include -Wunreachable-code, similar to how
> it was in gcc 3.3.

-Wunreachable-code was not in included with -Wall in 3.3 but a different
warning was enabled for this.


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=25314

[Bug c/25314] [3.4/4.0/4.1/4.2 Regression] Unreachable code at beginning of switch statement is not reported anymore

[Uwe dot Seimet at seimet dot de]

------- Comment #4 from Uwe dot Seimet at seimet dot de  2005-12-08 19:05 -------
Subject: Re:  [3.4/4.0/4.1/4.2 Regression] Unreachable code at beginning of
switch statement is not reported anymore

Hello,

> > It would be nice for -Wall to include -Wunreachable-code, similar to how
> > it was in gcc 3.3.
> 
> -Wunreachable-code was not in included with -Wall in 3.3 but a different
> warning was enabled for this.

Yes, but at least there was a warning (even though a different one) when
using gcc 3.3 and -Wall. With 4.0.2 and -Wall there is no warning at all.
If I had not still been using 3.3 while migrating to 4.0.2 I would never
have found this bug in my code, because 4.0.2 did not report it with
-Wall.

Best regards,   Uwe


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=25314

[Bug c/25314] [3.4/4.0/4.1/4.2 Regression] Unreachable code at beginning of switch statement is not reported anymore

[pinskia at gcc dot gnu dot org]

------- Comment #5 from pinskia at gcc dot gnu dot org  2005-12-12 03:01 -------
: Search converges between 2003-04-16-trunk (#231) and 2003-04-17-trunk (#232).

>From that I almost think it was orginally caused by (but I should note that the
4.0 regression would have been caused by the change over to tree-ssa):
2003-04-16  Roger Sayle  <roger@eyesopen.com> 

        * c-semantics.c (find_reachable_label): New function to find a
        potentially reachable label in an expression.
        (expand_unreachable_if_stmt): Similar to expand_if_stmt but
        assumes the start of the IF_STMT is unreachable (dead) code.
        (expand_unreachable_stmt): Similar to expand_stmt but assumes
        the start of the statement list is unreachable (dead) code.
        (genrtl_if_stmt):  If the controlling expression of the IF
        is constant, use expand_unreachable_stmt for the THEN or ELSE
        clause as appropriate.
        (genrtl_switch_stmt):  Use expand_unreachable_stmt to expand
        the body of a SWITCH statement.
        (expand_stmt): The code immediately following a "return",
        "break", "continue" or "goto" is unreachable.
        * Makefile.in (c-semantics.o): Depend upon tree-inline.h.


-- 

pinskia at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |roger at eyesopen dot com


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=25314

[Bug c/25314] [3.4/4.0/4.1/4.2 Regression] Unreachable code at beginning of switch statement is not reported anymore

[Uwe dot Seimet at seimet dot de]

------- Comment #6 from Uwe dot Seimet at seimet dot de  2005-12-12 06:21 -------
Subject: Re:  [3.4/4.0/4.1/4.2 Regression] Unreachable code at beginning of
switch statement is not reported anymore

Hello,

Another comment from my side: When using -Wunreachable-code as a means
to detect unreachable code in a switch statement I noticed that, just like
the manpage says, -Wunreachable-code issues a lot of warnings when compiling
with -g. There are so many warnings with "-g -Wunreachable-code" that it is
impossible to see which warning is justified and which is not.
The behavior with old versions of gcc was much more transparent. With gcc
3.3 I got an accurate warning for the unreachable code in the code sample I
sent you. Which gcc 4.0 I only get this warning with -Wunreachable-code,
but there are so many other (not useful) warnings that -Wunreachable-code
is not a good solution wrt the switch statement.

Best regards,   Uwe


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=25314

[Bug c/25314] [3.4/4.0/4.1/4.2 Regression] Unreachable code at beginning of switch statement is not reported anymore

[mmitchel at gcc dot gnu dot org]

------- Comment #7 from mmitchel at gcc dot gnu dot org  2005-12-19 19:21 -------
I would definitely like to see this resolved, but it will never be
release-critical: P5.


-- 

mmitchel at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Priority|P3                          |P5


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=25314

[Bug c/25314] [3.4/4.0/4.1/4.2 Regression] Unreachable code at beginning of switch statement is not reported anymore

[mmitchel at gcc dot gnu dot org]

-- 

mmitchel at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Target Milestone|4.0.3                       |4.0.4


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=25314

[Bug c/25314] [4.0/4.1/4.2/4.3 Regression] Unreachable code at beginning of switch statement is not reported anymore

[gdr at gcc dot gnu dot org]

------- Comment #8 from gdr at gcc dot gnu dot org  2007-02-03 16:06 -------
Won't fix in GCC-4.0.x.  Adjusting milestone.


-- 

gdr at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Target Milestone|4.0.4                       |---


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=25314

[Bug c/25314] [4.0/4.1/4.2/4.3 Regression] Unreachable code at beginning of switch statement is not reported anymore

[jsm28 at gcc dot gnu dot org]

-- 

jsm28 at gcc dot gnu dot org changed:

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


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=25314

[Bug c/25314] [4.0/4.1/4.2/4.3 Regression] Unreachable code at beginning of switch statement is not reported anymore

[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=25314

[Bug c/25314] [4.2/4.3/4.4 Regression] Unreachable code at beginning of switch statement is not reported anymore

[jsm28 at gcc dot gnu dot org]

------- Comment #9 from jsm28 at gcc dot gnu dot org  2008-07-04 20:15 -------
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]
                   |Unreachable code at         |Unreachable code at
                   |beginning of switch         |beginning of switch
                   |statement is not reported   |statement is not reported
                   |anymore                     |anymore
   Target Milestone|4.1.3                       |4.2.5


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=25314

[Bug c/25314] [4.2/4.3/4.4 Regression] Unreachable code at beginning of switch statement is not reported anymore

[steven at gcc dot gnu dot org]

------- Comment #10 from steven at gcc dot gnu dot org  2008-12-11 00:10 -------
Created an attachment (id=16882)
 --> (http://gcc.gnu.org/bugzilla/attachment.cgi?id=16882&action=view)
proposed patch

Looking for comments in this patch...


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=25314

[Bug c/25314] [4.2/4.3/4.4 Regression] Unreachable code at beginning of switch statement is not reported anymore

[steven at gcc dot gnu dot org]

-- 

steven at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
         AssignedTo|unassigned at gcc dot gnu   |steven at gcc dot gnu dot
                   |dot org                     |org
             Status|UNCONFIRMED                 |ASSIGNED
     Ever Confirmed|0                           |1
   Last reconfirmed|0000-00-00 00:00:00         |2008-12-11 00:35:40
               date|                            |


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=25314

[Bug c/25314] [4.2/4.3/4.4 Regression] Unreachable code at beginning of switch statement is not reported anymore

[jakub at gcc dot gnu dot org]

------- Comment #11 from jakub at gcc dot gnu dot org  2008-12-11 08:45 -------
You do not to warn for:
void foo (int c)
{
  int a;
  switch (c)
    {
    foo:
      a = 1;
      break;
    case 5:
      goto foo;
    }
}
(any label should stop the search).
You ICE on:
void foo (int c)
{
  switch (c)
    {
      int a;
    case 5:
      a = 1;
      break;
    }
}
plus the CASE_LABEL_EXPR (or LABEL_EXPR) can be nested in arbitrary amount of
STATEMENT_LIST/BIND_EXPRs (not sure about e.g. try blocks etc.).


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=25314

[Bug c/25314] [4.2/4.3/4.4 Regression] Unreachable code at beginning of switch statement is not reported anymore

[steven at gcc dot gnu dot org]

------- Comment #12 from steven at gcc dot gnu dot org  2009-03-08 21:40 -------
Not working on this anymore.  Can't get it to produce sensible warnings...


-- 

steven at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
         AssignedTo|steven 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=25314

[Bug c/25314] [4.3/4.4/4.5 Regression] Unreachable code at beginning of switch statement is not reported anymore

[jsm28 at gcc dot gnu dot org]

------- Comment #13 from jsm28 at gcc dot gnu dot org  2009-03-31 19:03 -------
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]
                   |Unreachable code at         |Unreachable code at
                   |beginning of switch         |beginning of switch
                   |statement is not reported   |statement is not reported
                   |anymore                     |anymore
   Target Milestone|4.2.5                       |4.3.4


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=25314

[Bug c/25314] [4.3/4.4/4.5 Regression] Unreachable code at beginning of switch statement is not reported anymore

[rguenth at gcc dot gnu dot org]

------- Comment #14 from rguenth at gcc dot gnu dot org  2009-08-04 12:27 -------
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=25314

[Bug c/25314] [4.3/4.4/4.5 Regression] Unreachable code at beginning of switch statement is not reported anymore

[rguenth at gcc dot gnu dot org]

------- Comment #15 from rguenth at gcc dot gnu dot org  2010-01-17 10:22 -------
-Wunreachable-code has been removed.


-- 

rguenth at gcc dot gnu dot org changed:

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


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=25314