[Bug middle-end/42674] New: Bogus "no return statement in function returning non-void" warning

[Bug middle-end/42674] New: Bogus "no return statement in function returning non-void" warning

[davek at gcc dot gnu dot org]

Simple testcase not even worth attaching preprocessed source for, using
HEAD@155680.  Note that this only arises in C++, not when compiled as C:

------------------------------------------------------------------------
$ cat badwarn.cpp

extern void bar (void);
int foo (void) __attribute__ ((__noreturn__));

int
foo (void)
{
  while (1)
  {
    bar ();
  }
}

$ g++-4 -c badwarn.cpp  -Wall
badwarn.cpp: In function 'int foo()':
badwarn.cpp:12:1: warning: no return statement in function returning non-void
------------------------------------------------------------------------

Discussed on the list at http://gcc.gnu.org/ml/gcc/2010-01/threads.html#00180;
Ross Smith identified this as a regression as it does not arise with 4.0.1,
4.2.1 and 4.3.4, and HJ tracked it to r.138140:

http://gcc.gnu.org/ml/gcc-cvs/2008-07/msg00852.html


-- 
           Summary: Bogus "no return statement in function returning non-
                    void" warning
           Product: gcc
           Version: 4.5.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: middle-end
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: davek at gcc dot gnu dot org
 GCC build triplet: i686-pc-cygwin
  GCC host triplet: i686-pc-cygwin
GCC target triplet: i686-pc-cygwin


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=42674

[Bug middle-end/42674] [4.5 Regression] Bogus "no return statement in function returning non-void" warning

[hjl dot tools at gmail dot com]

-- 

hjl dot tools at gmail dot com changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |hubicka at gcc dot gnu dot
                   |                            |org
             Status|UNCONFIRMED                 |NEW
     Ever Confirmed|0                           |1
  GCC build triplet|i686-pc-cygwin              |
   GCC host triplet|i686-pc-cygwin              |
 GCC target triplet|i686-pc-cygwin              |
   Last reconfirmed|0000-00-00 00:00:00         |2010-01-09 20:49:10
               date|                            |


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=42674

[Bug middle-end/42674] [4.4/4.5 Regression] Bogus "no return statement in function returning non-void" warning

[rguenth at gcc dot gnu dot org]

------- Comment #1 from rguenth at gcc dot gnu dot org  2010-01-10 22:08 -------
We should probably warn instead "function returning non-void declared with
attribute noreturn".


-- 

rguenth at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
      Known to fail|                            |4.4.2 4.5.0
      Known to work|                            |4.3.4
            Summary|[4.5 Regression] Bogus "no  |[4.4/4.5 Regression] Bogus
                   |return statement in function|"no return statement in
                   |returning non-void" warning |function returning non-void"
                   |                            |warning
   Target Milestone|---                         |4.4.3


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=42674

[Bug middle-end/42674] [4.4/4.5 Regression] Bogus "no return statement in function returning non-void" warning

[davek at gcc dot gnu dot org]

------- Comment #2 from davek at gcc dot gnu dot org  2010-01-11 00:23 -------
(In reply to comment #1)
> We should probably warn instead "function returning non-void declared with
> attribute noreturn".
> 

I think not; I don't see why you should be obliged to change the prototype of a
function in order to tell the compiler that it does not return, and it's very
often the case that you can't control the prototype of a function.  The
particular example this came from was a thread function that was spawned by
pthread_create, so it had to have an int return type, even though it had a
while (1) loop that meant it never would, in fact return; I wanted to tell the
compiler that.

Note however that I only included noreturn to show that it doesn't suppress the
warning; the warning arises even without it (as I mentioned in the list thread
but see I forgot to mention earlier here; sorry).  The real problem is that it
shouldn't complain about a missing return statement if there's no possible way
of exiting the function.


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=42674

[Bug middle-end/42674] [4.4/4.5 Regression] Bogus "no return statement in function returning non-void" warning

[manu at gcc dot gnu dot org]

------- Comment #3 from manu at gcc dot gnu dot org  2010-01-11 18:17 -------
There must be some reason why this:

  if (warn_return_type
      && TREE_CODE (TREE_TYPE (TREE_TYPE (fndecl))) != VOID_TYPE
      && !current_function_returns_value && !current_function_returns_null
      /* Don't complain if we are no-return.  */
      && !current_function_returns_abnormally
      /* Don't warn for main().  */
      && !MAIN_NAME_P (DECL_NAME (fndecl))
      /* Or if they didn't actually specify a return type.  */
      && !C_FUNCTION_IMPLICIT_INT (fndecl)
      /* Normally, with -Wreturn-type, flow will complain, but we might
         optimize out static functions.  */
      && !TREE_PUBLIC (fndecl))
    {
      warning (OPT_Wreturn_type,
               "no return statement in function returning non-void");
      TREE_NO_WARNING (fndecl) = 1;
    }

is not triggered in C (even without the __noreturn__?), whereas this is:

  if (warn_return_type
      && TREE_CODE (TREE_TYPE (fntype)) != VOID_TYPE
      && !dependent_type_p (TREE_TYPE (fntype))
      && !current_function_returns_value && !current_function_returns_null
      /* Don't complain if we abort or throw.  */
      && !current_function_returns_abnormally
      && !DECL_NAME (DECL_RESULT (fndecl))
      && !TREE_NO_WARNING (fndecl)
      /* Structor return values (if any) are set by the compiler.  */
      && !DECL_CONSTRUCTOR_P (fndecl)
      && !DECL_DESTRUCTOR_P (fndecl))
    {
      warning (OPT_Wreturn_type,
               "no return statement in function returning non-void");
      TREE_NO_WARNING (fndecl) = 1;
    }

I think this may be actually two bugs, one is the noreturn which should set
current_function_returns_abnormally to true, so no warning. Another is that the
function is not marked as never returning because of the infinite loop.


-- 

manu at gcc dot gnu dot org changed:

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


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=42674

[Bug middle-end/42674] [4.4/4.5 Regression] Bogus "no return statement in function returning non-void" warning

[davek at gcc dot gnu dot org]

------- Comment #4 from davek at gcc dot gnu dot org  2010-01-11 19:07 -------
(In reply to comment #3)
> (even without the __noreturn__?)

  Yes, even without.

> I think this may be actually two bugs, one is the noreturn which should set
> current_function_returns_abnormally to true, so no warning. Another is that the
> function is not marked as never returning because of the infinite loop.

  Sounds right to me.  Ok to leave them both under this one PR, or should we
separate them?


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=42674

[Bug middle-end/42674] [4.4/4.5 Regression] Bogus "no return statement in function returning non-void" warning

[jakub at gcc dot gnu dot org]

------- Comment #5 from jakub at gcc dot gnu dot org  2010-01-13 17:38 -------
The difference between C and C++ FE is just r138140, i.e. the && !TREE_PUBLIC
check.
Just try
extern void bar (void);
static int foo (void) __attribute__ ((__noreturn__, __used__));

static int
foo (void)
{
  while (1)
    bar ();
}

which warns both in C and C++.  I guess we should just add !TREE_THIS_VOLATILE
(fndecl) check to both C and C++ FE.


-- 

jakub at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
         AssignedTo|unassigned at gcc dot gnu   |jakub at gcc dot gnu dot org
                   |dot org                     |
             Status|NEW                         |ASSIGNED
   Last reconfirmed|2010-01-09 20:49:10         |2010-01-13 17:38:25
               date|                            |


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=42674

[Bug middle-end/42674] [4.4/4.5 Regression] Bogus "no return statement in function returning non-void" warning

[jakub at gcc dot gnu dot org]

------- Comment #6 from jakub at gcc dot gnu dot org  2010-01-13 18:07 -------
Created an attachment (id=19578)
 --> (http://gcc.gnu.org/bugzilla/attachment.cgi?id=19578&action=view)
gcc45-pr42674.patch

Patch I'm going to bootstrap/regtest.


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=42674

[Bug middle-end/42674] [4.4/4.5 Regression] Bogus "no return statement in function returning non-void" warning

[rguenth at gcc dot gnu dot org]

-- 

rguenth at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Priority|P3                          |P2


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=42674

[Bug middle-end/42674] [4.4/4.5 Regression] Bogus "no return statement in function returning non-void" warning

[jakub at gcc dot gnu dot org]

------- Comment #7 from jakub at gcc dot gnu dot org  2010-01-14 22:44 -------
Subject: Bug 42674

Author: jakub
Date: Thu Jan 14 22:43:56 2010
New Revision: 155920

URL: http://gcc.gnu.org/viewcvs?root=gcc&view=rev&rev=155920
Log:
        PR middle-end/42674
        * c-decl.c (finish_function): Don't emit -Wreturn-type warnings in
        functions with noreturn attribute.

        * decl.c (finish_function): Don't emit -Wreturn-type warnings in
        functions with noreturn attribute.

        * c-c++-common/pr42674.c: New test.

Added:
    trunk/gcc/testsuite/c-c++-common/pr42674.c
Modified:
    trunk/gcc/ChangeLog
    trunk/gcc/c-decl.c
    trunk/gcc/cp/ChangeLog
    trunk/gcc/cp/decl.c
    trunk/gcc/testsuite/ChangeLog


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=42674

[Bug middle-end/42674] [4.4/4.5 Regression] Bogus "no return statement in function returning non-void" warning

[jakub at gcc dot gnu dot org]

------- Comment #8 from jakub at gcc dot gnu dot org  2010-01-14 22:49 -------
Subject: Bug 42674

Author: jakub
Date: Thu Jan 14 22:49:17 2010
New Revision: 155922

URL: http://gcc.gnu.org/viewcvs?root=gcc&view=rev&rev=155922
Log:
        PR middle-end/42674
        * c-decl.c (finish_function): Don't emit -Wreturn-type warnings in
        functions with noreturn attribute.

        * decl.c (finish_function): Don't emit -Wreturn-type warnings in
        functions with noreturn attribute.

        * c-c++-common/pr42674.c: New test.

Added:
    branches/gcc-4_4-branch/gcc/testsuite/c-c++-common/pr42674.c
Modified:
    branches/gcc-4_4-branch/gcc/ChangeLog
    branches/gcc-4_4-branch/gcc/c-decl.c
    branches/gcc-4_4-branch/gcc/cp/ChangeLog
    branches/gcc-4_4-branch/gcc/cp/decl.c
    branches/gcc-4_4-branch/gcc/testsuite/ChangeLog


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=42674

[Bug middle-end/42674] [4.4/4.5 Regression] Bogus "no return statement in function returning non-void" warning

[jakub at gcc dot gnu dot org]

------- Comment #9 from jakub at gcc dot gnu dot org  2010-01-14 23:19 -------
Fixed.


-- 

jakub at gcc dot gnu dot org changed:

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


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=42674