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* [Bug c/61534] New: Wlogical-op should not warn when either operand comes from macro expansion
@ 2014-06-17 10:25 manu at gcc dot gnu.org
  2014-06-25 17:53 ` [Bug c/61534] " mpolacek at gcc dot gnu.org
                   ` (5 more replies)
  0 siblings, 6 replies; 7+ messages in thread
From: manu at gcc dot gnu.org @ 2014-06-17 10:25 UTC (permalink / raw)
  To: gcc-bugs

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=61534

            Bug ID: 61534
           Summary: Wlogical-op should not warn when either operand comes
                    from macro expansion
           Product: gcc
           Version: 4.10.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c
          Assignee: unassigned at gcc dot gnu.org
          Reporter: manu at gcc dot gnu.org

#define DEFINED (x != 0)

int foo(int x)
{
  if (!DEFINED && x != 0) return 0;
  return 1;
}

manuel@gcc10:~$ ~/test1/210581/build/gcc/cc1 -Wlogical-op test.c
 foo
test.c: In function ‘foo’:
test.c:5:16: warning: logical ‘and’ of mutually exclusive tests is always false
[-Wlogical-op]
   if (!DEFINED && x != 0) return 0;
                ^

Clang does not warn. This was the reason -Wlogical-op was moved out of -Wextra
(PR40172).
>From gcc-bugs-return-454370-listarch-gcc-bugs=gcc.gnu.org@gcc.gnu.org Tue Jun 17 10:33:59 2014
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From: "manu at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug c/60759] improve -Wlogical-op
Date: Tue, 17 Jun 2014 10:33:00 -0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=60759

Manuel López-Ibáñez <manu at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |NEW
   Last reconfirmed|                            |2014-06-17
            Summary|-Wlogical-op should perhaps |improve -Wlogical-op
                   |warn about two-way implicit |
                   |conversions                 |
     Ever confirmed|0                           |1

--- Comment #4 from Manuel López-Ibáñez <manu at gcc dot gnu.org> ---
GCC's -Wlogical-op warns for this:

pr60759.c:6:12: warning: logical ‘or’ applied to non-boolean constant
[-Wlogical-op]
   return y || 3;
            ^

However, GCC does not warn when both operands are constants or neither is a
constant. I think it is clear that it should warn for the former case. The
conditions at which it should warn are the same (it warns even if the result is
used in a boolean context).

The latter case is more controversial. Moreover, in this case the context is
significant:

int a = foo(1) || foo(2);  // warn
bool a = foo(1) || foo(2);  // do NOT warn

Someone would need to check how much code will be wrongly warned and how to
minimize the amount of false positives.
>From gcc-bugs-return-454371-listarch-gcc-bugs=gcc.gnu.org@gcc.gnu.org Tue Jun 17 10:34:05 2014
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From: "manu at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug c/53131] -Wlogical-op: ready for prime time in -Wall ?
Date: Tue, 17 Jun 2014 10:34:00 -0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=53131

--- Comment #8 from Manuel López-Ibáñez <manu at gcc dot gnu.org> ---
(In reply to Manuel López-Ibáñez from comment #7)
> In fact, the main show-stopper for adding -Wlogical-op to -Wextra (or -Wall)
> is PR40172, which was the reason it was moved out of -Wextra in the first
> place. 

Since PR40172 was closed without fixing the real problem, I opened PR61534. As
far as I am aware, this is the only issue preventing -Wlogical-op to be moved
back to -Wextra. As always, patches welcome.
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From: "Ulrich.Windl at rz dot uni-regensburg.de" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug c++/61531] Optimizer completely removes some bitset code
Date: Tue, 17 Jun 2014 10:55:00 -0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?ida531

--- Comment #6 from Ulrich Windl <Ulrich.Windl at rz dot uni-regensburg.de> ---
(In reply to Richard Biener from comment #5)
> > rpm -q gcc43-c++
> gcc43-c++-4.3.4_20091019-0.22.17
> > rpm -q --changelog gcc43-c++ | head
> * Thu Nov 10 2011 rguenther@suse.com
> - Fix altivec comparison builtins.  [bnc#729378]

Could be SUSE-specific: Although I have all updates for the product installed,
my version is older (Fri Jan 09 2009, as indicated in comment #1).


^ permalink raw reply	[flat|nested] 7+ messages in thread
end of thread, other threads:[~2024-01-24  1:42 UTC | newest]

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-- links below jump to the message on this page --
2014-06-17 10:25 [Bug c/61534] New: Wlogical-op should not warn when either operand comes from macro expansion manu at gcc dot gnu.org
2014-06-25 17:53 ` [Bug c/61534] " mpolacek at gcc dot gnu.org
2014-06-25 18:09 ` manu at gcc dot gnu.org
2014-06-25 18:21 ` mpolacek at gcc dot gnu.org
2014-11-02  0:57 ` manu at gcc dot gnu.org
2015-04-24 11:50 ` mpolacek at gcc dot gnu.org
2024-01-24  1:42 ` mpolacek at gcc dot gnu.org

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