[Bug c/12603] New: No return statement warning on function that never returns with -O3

[Bug c/12603] New: No return statement warning on function that never returns with -O3

[james at ittc dot ku dot 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=12603

           Summary: No return statement warning on function that never
                    returns with -O3
           Product: gcc
           Version: 3.3.1
            Status: UNCONFIRMED
          Severity: minor
          Priority: P3
         Component: c
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: james at ittc dot ku dot edu
                CC: gcc-bugs at gcc dot gnu dot org,james at ittc dot ku dot
                    edu
 GCC build triplet: i686-pc-linux-gnu
  GCC host triplet: i686-pc-linux-gnu
GCC target triplet: i686-pc-linux-gnu

The following function compiles without warning at optimization level -O2 or
below.  With -Wall -O3, gcc says:

noreturn.c: In function `this_function_never_returns':
noreturn.c:5: warning: no return statement in function returning non-void

This happens with gcc 3.2.2 - 3.3.1, at least.

int
this_function_never_returns ()
{
  for (;;);
}

This is an extremely stripped down version of a problem with XEmacs and
Fcommand_loop_1, which must be declared to return a Lisp_Object (since it is a
Lisp-visible function), but which contains an infinite loop.  The obvious
solution of putting a return statement at the end causes some compilers to
complain about unreachable code.  Adding __attribute__ ((noreturn)) did not make
the warning go away.

[Bug optimization/12603] No return statement warning on function that never returns with -O3

[pinskia 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=12603


pinskia at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |NEW
          Component|c                           |optimization
     Ever Confirmed|                            |1
           Keywords|                            |diagnostic
   Last reconfirmed|0000-00-00 00:00:00         |2003-10-18 17:44:11
               date|                            |


------- Additional Comments From pinskia at gcc dot gnu dot org  2003-10-18 17:44 -------
This should not warn at -O3, I think this is related to the control flow graph some how.

[Bug optimization/12603] No return statement warning on function that never returns with -O3

[kazu at cs dot umass dot edu]

------- Additional Comments From kazu at cs dot umass dot edu  2003-11-24 20:54 -------
This problem does not seem to occur with gcc-3.4 20031124.


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=12603

[Bug optimization/12603] No return statement warning on function that never returns with -O3

[pinskia at gcc dot gnu dot org]

------- Additional Comments From pinskia at gcc dot gnu dot org  2003-11-24 22:51 -------
I can still reproduce it with the mainline (20031124).

-- 
           What    |Removed                     |Added
----------------------------------------------------------------------------
   Last reconfirmed|2003-10-18 17:44:11         |2003-11-24 22:51:09
               date|                            |


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=12603

[Bug c/12603] No return statement warning on function that never returns with -O3

[pinskia at gcc dot gnu dot org]

------- Additional Comments From pinskia at gcc dot gnu dot org  2004-03-06 05:48 -------
The problem is that -O3, DECL_INLINE for the function decl becomes true because -O3 
enables -finline-functions.  So it looks like a different check is needed for the C front-end.

-- 
           What    |Removed                     |Added
----------------------------------------------------------------------------
          Component|optimization                |c


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=12603

[Bug c/12603] No return statement warning on function that never returns with -O3

[zwin at users dot sourceforge dot net]

------- Additional Comments From zwin at users dot sourceforge dot net  2004-05-02 15:36 -------
I am also getting this warning about no return statement for methods in C++.
While a global function int noret() { for (;;); } does not fire the warning, the
same in a method does (3.2.3).

-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=12603