[Bug c/16302] New: gcc fails to warn about some common logic errors

[Bug c/16302] New: gcc fails to warn about some common logic errors

[trt at acm dot org]

A "gcc -Wextra -O" misses the 4 bugs in this test program:

int
main (int argc, char *argv[])
{
   if (argc != 1 || argc != 2) return 1;
   if (argc < 0 && argc > 10) return 1;
   if (argc || !argc) return 1;
   if (argc && !argc) return 1;
   return 0;
}

With a tweak to fold-const.c (below), they will be caught:

t.c:4: warning: `or' of collectively exhaustive tests is always 1
t.c:5: warning: `and' of mutually exclusive tests is always 0
t.c:6: warning: `or' of collectively exhaustive tests is always 1
t.c:7: warning: `and' of mutually exclusive tests is always 0

A bootstrap of gcc-3.5-20040627 reports such a warning in fold-const.c itself,
the patch below includes the obvious fix.

====
Comment: The -O is needed due to this code in fold-const.c:

      /* We only do these simplifications if we are optimizing.  */
      if (!optimize)
        return t;

This is probably from when fold-const.c was much simpler,
but I think is no longer appropriate and recommend it be deleted.
====

*** fold-const.c.orig   Sun Jun 27 11:23:44 2004
--- fold-const.c        Wed Jun 30 12:43:39 2004
***************
*** 4377,4379 ****
                                         in_p, low, high))))
!     return or_op ? invert_truthvalue (tem) : tem;
   
--- 4377,4388 ----
                                         in_p, low, high))))
!     {
!       if (TREE_CODE (tem) == INTEGER_CST && extra_warnings)
!         {
!           if (or_op)
!             warning ("`or' of collectively exhaustive tests is always 1");
!           else
!             warning ("`and' of mutually exclusive tests is always 0");
!         }
!       return or_op ? invert_truthvalue (tem) : tem;
!     }
   
***************
*** 9998,10000 ****
          || (TREE_CODE (op0) == REAL_CST
!             && TREE_CODE (op0) != REAL_CST))
        {
--- 10007,10009 ----
          || (TREE_CODE (op0) == REAL_CST
!             && TREE_CODE (op1) != REAL_CST))
        {

-- 
           Summary: gcc fails to warn about some common logic errors
           Product: gcc
           Version: 3.5.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P2
         Component: c
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: trt at acm dot org
                CC: gcc-bugs at gcc dot gnu dot org


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=16302

[Bug c/16302] gcc fails to warn about some common logic errors

[pinskia at gcc dot gnu dot org]

------- Additional Comments From pinskia at gcc dot gnu dot org  2004-07-01 01:23 -------
Confirmed, patches goto gcc-patches@ after reading http://gcc.gnu.org/contribute.html.

-- 
           What    |Removed                     |Added
----------------------------------------------------------------------------
           Keywords|                            |diagnostic


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=16302

[Bug c/16302] gcc fails to warn about some common logic errors

[trt at acm dot org]

------- Additional Comments From trt at acm dot org  2004-07-01 15:28 -------
It is not practical for gcc outsiders to submit patches,
the requirements are too exacting and complex.  E.g. see
http://gcc.gnu.org/ml/gcc-patches/2004-07/msg00072.html
which demands a testcase (something which is IMO unclear
in the "contributing" URL you gave).
It is unlikely my first (or second) attempt at a testcase
will be flawless.
Similarly, I am asked to document this warning
(which I find odd, since there are lots of undocumented -Wextra warnings).
Do I need to fix the "broken" existing warnings too?  The response was unclear.
The only requirement I can confidently handle is fixing the warning strings.
And are these *all* the requirements?  I doubt it.

On the other hand, such issues are trivial for veterans such as yourself.
Could you please handle this for me?  I would greatly appreciate it.

-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=16302

[Bug c/16302] gcc fails to warn about some common logic errors

[bangerth at dealii dot org]

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


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=16302

[Bug c/16302] gcc fails to warn about some common logic errors

[jsm at polyomino dot org dot uk]

------- Additional Comments From jsm at polyomino dot org dot uk  2004-07-01 17:45 -------
Subject: Re:  gcc fails to warn about some common logic errors

On Thu, 1 Jul 2004, trt at acm dot org wrote:

> (which I find odd, since there are lots of undocumented -Wextra warnings).

Please report these as separate bugs.  Phil Edwards fixed the known such
problems in <http://gcc.gnu.org/ml/gcc-patches/2003-01/msg01741.html>; any
that have been added since then would be regressions.



-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=16302

[Bug c/16302] gcc fails to warn about some common logic errors

[trt at acm dot org]

------- Additional Comments From trt at acm dot org  2004-07-07 15:36 -------
I have submitted a revised patch in
http://gcc.gnu.org/ml/gcc-patches/2004-07/msg00148.html


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=16302

[Bug middle-end/16302] gcc fails to warn about some common logic errors

[pinskia at gcc dot gnu dot org]

------- Additional Comments From pinskia at gcc dot gnu dot org  2004-08-03 07:32 -------
Confirmed.

-- 
           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |NEW
          Component|c                           |middle-end
     Ever Confirmed|                            |1
           Keywords|                            |patch
   Last reconfirmed|0000-00-00 00:00:00         |2004-08-03 07:32:55
               date|                            |


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=16302

[Bug middle-end/16302] gcc fails to warn about some common logic errors

[trt at acm dot org]

------- Additional Comments From trt at acm dot org  2004-09-02 18:19 -------
Here are some reasons why I think this patch should be applied.
1.  Inspection of the patch will show that it is "low risk",
    except for the potential risk of false positives.
2.  I have been using this warning for about 4 years now,
    on a 35Mloc source code base involving 100s of developers,
    and it has triggered dozens of times with only a couple false positives.
    (The false positives do not happen with gcc 3.5, I think some changes
     to fold() have caused them to go away.)
    Sometimes, for fun, I use this compiler on other source code.
    E.g. I remember reporting two of these warnings (among others)
    in an early version of "valgrind".
3.  It spots 3 bugs in gcc 3.5.  One of them is fixed by this patch.
    If you want to see the other two, try applying the patch.

As a downside, some versions of gcc/insn-attrtab.c trigger these warnings.
Last I checked, the ia64 version had about 7 of them.
They are technically valid, but probably indicate harmless inefficiencies.
On the other hand, they might indicate something that should be cleaned up.

I realize there is no urgent need for this patch,
but I have seen much less effective (and sometimes counterproductive)
warning messages added to gcc.  Please consider one.

-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=16302

[Bug middle-end/16302] gcc fails to warn about some common logic errors

[trt at acm dot org]

------- Additional Comments From trt at acm dot org  2005-04-29 20:20 -------
The patch given in comment #4 no successfully applies because the warning()
function has new initial parameter.  Also the fold_buildN() cleanup invalidated
(and fixed) the "REAL_CST" part of the patch.
Some "speculative folding" is now causing false positives, for which there is a
simple fix: suppress warnings when doing such folds. For example

*** tree-ssa-loop-niter.c.orig  Wed Apr 27 13:48:21 2005
--- tree-ssa-loop-niter.c       Wed Apr 27 14:28:59 2005
***************
*** 778,780 ****
--- 778,782 ----
    notcond = invert_truthvalue (cond);
+   inhibit_warnings++;
    e = fold_build2 (TRUTH_OR_EXPR, boolean_type_node, notcond, te);
+   inhibit_warnings--;
    if (nonzero_p (e))

People who think warnings belong only in the front-end might balk.  I could
submit an alternate indirect check for this situation in parser_build_binary_op.
 It would be tidy, but would no longer warn about non-C glitches such as:

libjava/gnu/java/security/x509/X500DistinguishedName.java:447:        if (sep !=
'+' || sep != ',')
libjava/java/net/HttpURLConnection.java:555:    if (((code / 100) != 4) ||
((code / 100) != 5))
libjava/javax/swing/plaf/basic/BasicGraphicsUtils.java:401:    if
((underlinedChar >= 0) || (underlinedChar <= 0xffff))
libjava/javax/security/auth/x500/X500Principal.java:380:        if (sep != '+'
|| sep != ',')

Please let me know if there is any interest in a C-only patch.  (Or any interest
in pursuing this PR.)

-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=16302

[Bug c/16302] gcc fails to warn about some common logic errors

[manu at gcc dot gnu dot org]

------- Comment #10 from manu at gcc dot gnu dot org  2009-05-15 20:10 -------
FIXED for GCC 4.5


-- 

manu at gcc dot gnu dot org changed:

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


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=16302

[Bug c/16302] gcc fails to warn about some common logic errors

[manu at gcc dot gnu dot org]

[-- Warning: decoded text below may be mangled, UTF-8 assumed --]
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------- Comment #9 from manu at gcc dot gnu dot org  2009-05-15 20:08 -------
Subject: Bug 16302

Author: manu
Date: Fri May 15 20:08:21 2009
New Revision: 147596

URL: http://gcc.gnu.org/viewcvs?root=gcc&view=rev&rev=147596
Log:
2009-05-15  Manuel López-Ibáñez  <manu@gcc.gnu.org>

        PR 16302
        * fold-const.c (make_range,build_range_check,merge_ranges): Move
        declaration to...
        (merge_ranges): Returns bool. 
        * tree.h (make_range): .. to here.
        (build_range_check): Likewise.
        (merge_ranges): Likewise. Renamed from merge_ranges.
        * c-typeck.c (parser_build_binary_op): Update calls to
        warn_logical_operator.
        * c-common.c (warn_logical_operator): Add new warning.
        * c-common.h (warn_logical_operator): Update declaration.
cp/
        * call.c (build_new_op): Update calls to warn_logical_operator.

testsuite/
        * gcc.dg/pr16302.c: New.
        * g++.dg/warn/pr16302.C: New.

Added:
    trunk/gcc/testsuite/g++.dg/warn/pr16302.C
    trunk/gcc/testsuite/gcc.dg/pr16302.c
Modified:
    trunk/gcc/ChangeLog
    trunk/gcc/c-common.c
    trunk/gcc/c-common.h
    trunk/gcc/c-typeck.c
    trunk/gcc/cp/ChangeLog
    trunk/gcc/cp/call.c
    trunk/gcc/fold-const.c
    trunk/gcc/testsuite/ChangeLog
    trunk/gcc/tree.h


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=16302

[Bug c/16302] gcc fails to warn about some common logic errors

[manu at gcc dot gnu dot org]

------- Comment #8 from manu at gcc dot gnu dot org  2007-02-13 16:55 -------
I wish to answer this because I am also a newbie and I understand your
frustration. On the other hand, I also understand why the current situation is
as it is now.

(In reply to comment #2)
> It is not practical for gcc outsiders to submit patches,
> the requirements are too exacting and complex.  E.g. see
> http://gcc.gnu.org/ml/gcc-patches/2004-07/msg00072.html
> which demands a testcase (something which is IMO unclear
> in the "contributing" URL you gave).

The requirements are documented. Unfortunately, the documentation is divided
among many places and not in the best form. It would be superb and very welcome
if someone took the responsibility of summarizing, re-writting and improving
the different pieces, so they can be as clear and simple as possible. (Like a
step by step guide on how to contribute, maybe especialised for different
user-cases).

Sadly, experienced people don't have time (and perhaps are not very well
suited) for this job. Someone brave needs to step up and take the burden,
perhaps seek collaborators among other frustrated newbies.

Another problem is that as soon as a newbie becomes experienced with the
procedure, then the interest in improving the docs fades away :(

> It is unlikely my first (or second) attempt at a testcase
> will be flawless.

It doesn't matter, reviewers should catch any flaw and patches are regularly
submitted many times. It is part of the learning proccess. Flawless patches are
accepted earlier, though. ;-)

> Similarly, I am asked to document this warning
> (which I find odd, since there are lots of undocumented -Wextra warnings).
> Do I need to fix the "broken" existing warnings too?  The response was unclear.

That is not an excuse. There are things that are historically wrong. New
mistakes cannot be justified based on past mistakes. New warnings should be
documented.

Normally, you don't need to fix anything that is broken already as long as it
is not closely related to your patch. 

If the response was unclear, you have to insist. No all mails are neccessarily
read by all people and people are busy busy busy (or on holidays), so sometimes
your mail will get lost. Wait one week and insist again. Wait another week and
keep insisting. Eventually someone will answer. Short and polite emails get
more answers than angry, long rants.

This also applies to patches. If you patch is not reviewed: wait one week and
insist. Repeat until reviewed.

> The only requirement I can confidently handle is fixing the warning strings.
> And are these *all* the requirements?  I doubt it.

It is very likely that if a reviewer finds an obvious mistake in your patch,
he/she will not review in deep the rest of it and just move on to the next
patch. You will need to send it again and wait for the answer. At first you
will make a lot of mistakes but that is normal. My first patch was rejected
several times just for the Changelog format. In a few iterations your patches
will be almost perfect.

> On the other hand, such issues are trivial for veterans such as yourself.
> Could you please handle this for me?  I would greatly appreciate it.

That is a sad misconception. Bootstrapping + testing take time even if there
are no failures at all. Adding testcases takes time. Having patches around
takes thinking time. Keeping track of submitted patches and pinging reviewers
take time. Fixing minor issues in patches takes time. Committing patches takes
also a  little amount of time. Of course, the total time could be trivial if
you had nothing else to do. But if the issue is minor and you are busy (or you
are not paid for fixing it and just prefer to invest your time in something
else like your family), then it is already too much time.

Also there is the issue (I guess) that if sloppy patches are regularly fixed by
reviewers, that will advocate more sloppy patches which in turn will make
reviewers more unwilling to review patches.

So please, reconsiderate your stance, and resubmit your patch. I am sure your
contribution will be appreciated.

Thanks in advance.


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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=16302