[Bug c++/36254] New: wrong "control reaches end of non-void function" warning

[Bug c++/36254] New: wrong "control reaches end of non-void function" warning

[pluto at agmk dot net]

$ g++ t1.cpp -Wall -c
t1.cpp: In function 'bool f()':
t1.cpp:10: warning: control reaches end of non-void function

$ g++ t2.cpp -Wall -c
t2.cpp: In function 'bool f(int)':
t2.cpp:16: warning: control reaches end of non-void function

tested on 4.1.2, 4.2.3-20080201 and 4.3.0-20080417


-- 
           Summary: wrong "control reaches end of non-void function" warning
           Product: gcc
           Version: 4.3.1
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: pluto at agmk dot net
  GCC host triplet: x86_64-gnu-linux


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=36254

[Bug c++/36254] wrong "control reaches end of non-void function" warning

[pluto at agmk dot net]

------- Comment #2 from pluto at agmk dot net  2008-05-17 09:54 -------
Created an attachment (id=15648)
 --> (http://gcc.gnu.org/bugzilla/attachment.cgi?id=15648&action=view)
testcase.


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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=36254

[Bug c++/36254] wrong "control reaches end of non-void function" warning

[pluto at agmk dot net]

------- Comment #1 from pluto at agmk dot net  2008-05-17 09:54 -------
Created an attachment (id=15647)
 --> (http://gcc.gnu.org/bugzilla/attachment.cgi?id=15647&action=view)
testcase.


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=36254

[Bug c++/36254] wrong "control reaches end of non-void function" warning

[pluto at agmk dot net]

------- Comment #3 from pluto at agmk dot net  2008-05-17 11:13 -------
4.4.0-20080517 also fails.


-- 

pluto at agmk dot net changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
      Known to fail|4.1.2 4.2.3 4.3.0           |4.1.2 4.2.3 4.3.0 4.4.0


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=36254

[Bug c++/36254] wrong "control reaches end of non-void function" warning

[rguenth at gcc dot gnu dot org]

------- Comment #4 from rguenth at gcc dot gnu dot org  2008-05-17 12:56 -------
Confirmed.  At -O0 we have after CFG building (t1.cpp)

  # BLOCK 8
  # PRED: 5 (fallthru) 6 (fallthru) 7 (fallthru)
<L6>:;
  __comp_dtor  (&x);
  switch (finally_tmp.3)
    {
      case 1: goto <L7>;
      default : goto <L8>;
    }
  # SUCC: 9 10

  # BLOCK 9
  # PRED: 8
<L7>:;
  return;
  # SUCC: EXIT


This would fix it.

Index: tree-eh.c
===================================================================
--- tree-eh.c   (revision 135433)
+++ tree-eh.c   (working copy)
@@ -1350,9 +1350,6 @@ decide_copy_try_finally (int ndests, tre
 {
   int f_estimate, sw_estimate;

-  if (!optimize)
-    return false;
-
   /* Finally estimate N times, plus N gotos.  */
   f_estimate = estimate_num_insns (finally, &eni_size_weights);
   f_estimate = (f_estimate + 1) * ndests;


-- 

rguenth at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |NEW
     Ever Confirmed|0                           |1
   Last reconfirmed|0000-00-00 00:00:00         |2008-05-17 12:56:06
               date|                            |


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=36254

[Bug c++/36254] wrong "control reaches end of non-void function" warning

[pluto at agmk dot net]

------- Comment #5 from pluto at agmk dot net  2008-05-25 19:20 -------
(In reply to comment #4)
> This would fix it.

4.3.1-20080525 with this patch seems to work fine.

> 
> Index: tree-eh.c
> ===================================================================
> --- tree-eh.c   (revision 135433)
> +++ tree-eh.c   (working copy)
> @@ -1350,9 +1350,6 @@ decide_copy_try_finally (int ndests, tre
>  {
>    int f_estimate, sw_estimate;
> 
> -  if (!optimize)
> -    return false;
> -
>    /* Finally estimate N times, plus N gotos.  */
>    f_estimate = estimate_num_insns (finally, &eni_size_weights);
>    f_estimate = (f_estimate + 1) * ndests;


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=36254

[Bug c++/36254] wrong "control reaches end of non-void function" warning

[manu at gcc dot gnu dot org]

------- Comment #6 from manu at gcc dot gnu dot org  2008-08-25 11:16 -------
We should not warn for compiler-generated code anyway. We need to find where
this is generated and then we need to check before warning.


-- 

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=36254

[Bug c++/36254] wrong "control reaches end of non-void function" warning

[manu at gcc dot gnu dot org]

------- Comment #7 from manu at gcc dot gnu dot org  2008-10-22 18:19 -------
The return is generated because we generate one (if there is none) everytime we
reach the end of a function. This is used later to produce "control reaches end
of non-void function". The compiler-generated try-catch forces the creation of
this extra return. The problem is that we do not want to mark all generated
return with no_warning, because we will miss valid warnings. Not sure yet how
to detect which ones were generated because we naturally reach the end of a
function or they are forced because of compiler-generated code.


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=36254

[Bug c++/36254] wrong "control reaches end of non-void function" warning

[jakub at gcc dot gnu dot org]

------- Comment #8 from jakub at gcc dot gnu dot org  2008-10-27 12:23 -------
The problem is that during gimplification shortcut_cond_expr doesn't detect
that then_ can't fallthru, if it detected that, then no jump around the else
block would be added and control reaches end of non-void function wouldn't
be diagnosed.
shortcut_cond_expr calls block_may_fallthru, unfortunately in C++ then then_
block isn't something block_may_fallthru handles - it is IF_STMT in the first
testcase, which is a C++ specific tree.
To fix this, either we'd need to do short cut on tuples (where
gimple_seq_may_fallthru handles all the gimple codes correctly), but I guess
that's quite hard, or we'd need some flag with which shortcut_cond_expr would
mark the maybe not needed GOTO_EXPR + LABEL_EXPR and during gimplification
see if sequence before so marked GOTO_EXPR might fallthru and if not, don't add
the GIMPLE_GOTO nor GIMPLE_LABEL.  Or block_may_fallthru would need to call a
langhook to handle unknown cases and each frontend would need to say what can
and what can't fallthru from the lang specific tree codes.


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=36254

[Bug c++/36254] wrong "control reaches end of non-void function" warning

[manu at gcc dot gnu dot org]

------- Comment #9 from manu at gcc dot gnu dot org  2008-10-27 12:42 -------
What is an IF_STMT?

Is block_may_fallthru a middle-end function, then why it is seeing front-end
tree codes? Is it not, then why each front-end does not have its own version
(perhaps sharing some common part)?

Dumping this code with -fdump-tree-original is also broken.
I wish there was a way to make compilation of GCC fail every time a front-end
tree code is added and it is not handled in all relevant places.

Jakub, are you going to work on a fix?


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=36254

[Bug c++/36254] wrong "control reaches end of non-void function" warning

[jakub at gcc dot gnu dot org]

------- Comment #10 from jakub at gcc dot gnu dot org  2008-10-27 14:05 -------
Language specific tree codes are allowed until the gimplification is done,
the cp_gimplify_expr langhook takes care of either rewriting the lang specific
tree code into GENERIC (COND_EXPR in this case), or tuplifying it right away.

BTW, looking at the other testcase, block_may_fallthru certainly isn't able
to say whether a SWITCH_EXPR can fall thru or not, and it wouldn't be actually
very easy.  So perhaps we either need to run some pass that kills obvious dead
code before reporting the "control reaches end" warnings, or really try harder
during gimplification to figure out these cases and optimize it at that point.

I'm not working on this ATM.


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=36254

[Bug c++/36254] wrong "control reaches end of non-void function" warning

[manu at gcc dot gnu dot org]

------- Comment #11 from manu at gcc dot gnu dot org  2008-10-27 14:35 -------
(In reply to comment #10)
> Language specific tree codes are allowed until the gimplification is done,
> the cp_gimplify_expr langhook takes care of either rewriting the lang specific
> tree code into GENERIC (COND_EXPR in this case), or tuplifying it right away.

If they are permitted, they should be handled. If they are not handled, we
should fail to compile or crash. Currently we just ignore them, which works ok
for C since generic is basically C but fails for everything else.

> BTW, looking at the other testcase, block_may_fallthru certainly isn't able
> to say whether a SWITCH_EXPR can fall thru or not, and it wouldn't be actually
> very easy.  So perhaps we either need to run some pass that kills obvious dead
> code before reporting the "control reaches end" warnings, or really try harder
> during gimplification to figure out these cases and optimize it at that point.

So basically you propose to do optimizations at -O0. I still do not understand
what is the problem with setting no_warning. This is *really*
compiler-generated code.


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=36254

[Bug c++/36254] wrong "control reaches end of non-void function" warning

[pinskia at gcc dot gnu dot org]

------- Comment #12 from pinskia at gcc dot gnu dot org  2008-12-28 03:30 -------
t2.cpp is really PR 20681.


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=36254

[Bug c++/36254] [4.2/4.3/4.4 Regression] wrong "control reaches end of non-void function" warning with IF_STMT

[pinskia at gcc dot gnu dot org]

------- Comment #13 from pinskia at gcc dot gnu dot org  2008-12-28 03:34 -------
Let's make this bug about the t1.cpp which is an IF_STMT issue.

This was introduced by the tree-ssa merge.


-- 

pinskia at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Keywords|                            |diagnostic
      Known to fail|4.1.2 4.2.3 4.3.0 4.4.0     |4.0.1 4.1.2 4.2.3 4.3.0
                   |                            |4.4.0
      Known to work|                            |3.3
   Last reconfirmed|2008-05-17 12:56:06         |2008-12-28 03:34:23
               date|                            |
            Summary|wrong "control reaches end  |[4.2/4.3/4.4 Regression]
                   |of non-void function"       |wrong "control reaches end
                   |warning                     |of non-void function"
                   |                            |warning with IF_STMT
   Target Milestone|---                         |4.2.5


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=36254

[Bug c++/36254] [4.2/4.3/4.4 Regression] wrong "control reaches end of non-void function" warning with IF_STMT

[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=36254

[Bug c++/36254] [4.2/4.3/4.4 Regression] wrong "control reaches end of non-void function" warning with IF_STMT

[jakub at gcc dot gnu dot org]

------- Comment #14 from jakub at gcc dot gnu dot org  2009-01-11 21:15 -------
Subject: Bug 36254

Author: jakub
Date: Sun Jan 11 21:14:51 2009
New Revision: 143281

URL: http://gcc.gnu.org/viewcvs?root=gcc&view=rev&rev=143281
Log:
        PR c++/36254
        * cp-gimplify.c (genericize_if_stmt): Renamed from ...
        (gimplify_if_stmt): ... this.
        (cp_gimplify_expr): Don't handle IF_STMT here.
        (cp_genericize_r): Call genericize_if_stmt for IF_STMT.

        * g++.dg/warn/Wreturn-type-5.C: New test.

Added:
    trunk/gcc/testsuite/g++.dg/warn/Wreturn-type-5.C
Modified:
    trunk/gcc/cp/ChangeLog
    trunk/gcc/cp/cp-gimplify.c
    trunk/gcc/testsuite/ChangeLog


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=36254

[Bug c++/36254] [4.2/4.3 Regression] wrong "control reaches end of non-void function" warning with IF_STMT

[jakub at gcc dot gnu dot org]

------- Comment #15 from jakub at gcc dot gnu dot org  2009-01-11 21:32 -------
Fixed on the trunk.


-- 

jakub at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
      Known to fail|4.0.1 4.1.2 4.2.3 4.3.0     |4.0.1 4.1.2 4.2.3 4.3.0
                   |4.4.0                       |
      Known to work|3.3                         |3.3 4.4.0
            Summary|[4.2/4.3/4.4 Regression]    |[4.2/4.3 Regression] wrong
                   |wrong "control reaches end  |"control reaches end of non-
                   |of non-void function"       |void function" warning with
                   |warning with IF_STMT        |IF_STMT


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=36254

[Bug c++/36254] [4.2/4.3 Regression] wrong "control reaches end of non-void function" warning with IF_STMT

[pinskia at gcc dot gnu dot org]

------- Comment #16 from pinskia at gcc dot gnu dot org  2009-02-14 10:05 -------
*** Bug 39191 has been marked as a duplicate of this bug. ***


-- 

pinskia at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |alpha dot super-one at
                   |                            |laposte dot net


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=36254

[Bug c++/36254] [4.3 Regression] wrong "control reaches end of non-void function" warning with IF_STMT

[jsm28 at gcc dot gnu dot org]

------- Comment #17 from jsm28 at gcc dot gnu dot org  2009-03-31 20:51 -------
Closing 4.2 branch.


-- 

jsm28 at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
            Summary|[4.2/4.3 Regression] wrong  |[4.3 Regression] wrong
                   |"control reaches end of non-|"control reaches end of non-
                   |void function" warning with |void function" warning with
                   |IF_STMT                     |IF_STMT
   Target Milestone|4.2.5                       |4.3.4


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=36254

[Bug c++/36254] [4.3 Regression] wrong "control reaches end of non-void function" warning with IF_STMT

[rguenth at gcc dot gnu dot org]

------- Comment #18 from rguenth at gcc dot gnu dot org  2009-08-04 12:29 -------
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=36254

[Bug c++/36254] [4.3 Regression] wrong "control reaches end of non-void function" warning with IF_STMT

[rguenth at gcc dot gnu dot org]

------- Comment #19 from rguenth at gcc dot gnu dot org  2010-05-22 18:12 -------
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=36254

[Bug c++/36254] [4.3 Regression] wrong "control reaches end of non-void function" warning with IF_STMT

[pluto at agmk dot net]

------- Comment #20 from pluto at agmk dot net  2010-09-02 16:22 -------
*** Bug 45497 has been marked as a duplicate of this bug. ***


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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=36254