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* [Bug c/60090] New: For expression without ~, gcc -O1 emits "comparison of promoted ~unsigned with unsigned"
@ 2014-02-06  8:01 chengniansun at gmail dot com
  2014-02-06  8:27 ` [Bug c/60090] " mpolacek at gcc dot gnu.org
                   ` (5 more replies)
  0 siblings, 6 replies; 7+ messages in thread
From: chengniansun at gmail dot com @ 2014-02-06  8:01 UTC (permalink / raw)
  To: gcc-bugs

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=60090

            Bug ID: 60090
           Summary: For expression without ~, gcc -O1 emits "comparison of
                    promoted ~unsigned with unsigned"
           Product: gcc
           Version: 4.9.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c
          Assignee: unassigned at gcc dot gnu.org
          Reporter: chengniansun at gmail dot com

For the expression "(l ^ a) != b", gcc -O0 emits no warning, but gcc -O1 emits
a warning "comparison of promoted ~unsigned with unsigned". After checking the
gimple code, I found the optimization transforms the expression to a bitwise
not expression. 

However, in a syntactic perspective, the warning message is confusing, given
the fact that there is no '~' in this expression. 

$: cat s.c
int fn1(unsigned char a, unsigned char b) {
  const unsigned l = 4294967295u;
  return (l ^ a) != b;
}
$: gcc-trunk -c -Wsign-compare s.c
$: gcc-trunk -c -Wsign-compare s.c -O1
s.c: In function ‘fn1’:
s.c:3:18: warning: comparison of promoted ~unsigned with unsigned
[-Wsign-compare]
   return (l ^ a) != b;
                  ^
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From: "hubicka at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug ipa/59469] [4.8/4.9 Regression] LLVM build failure with gcc LTO
Date: Thu, 06 Feb 2014 08:10:00 -0000
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http://gcc.gnu.org/bugzilla/show_bug.cgi?idY469

--- Comment #45 from Jan Hubicka <hubicka at gcc dot gnu.org> ---
The bug here is that lto-cgraph.c still checks DECL_COMDAT as a condition if
symbol is duplicated or partitioned.  We really need to get the logic into
lto-cgraph.c and use same test at both places... Will do that tomorrow.


^ permalink raw reply	[flat|nested] 7+ messages in thread
end of thread, other threads:[~2023-05-20  4:38 UTC | newest]

Thread overview: 7+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2014-02-06  8:01 [Bug c/60090] New: For expression without ~, gcc -O1 emits "comparison of promoted ~unsigned with unsigned" chengniansun at gmail dot com
2014-02-06  8:27 ` [Bug c/60090] " mpolacek at gcc dot gnu.org
2014-02-06  8:32 ` mpolacek at gcc dot gnu.org
2014-02-06  9:42 ` mpolacek at gcc dot gnu.org
2014-02-06 12:54 ` manu at gcc dot gnu.org
2014-02-06 13:04 ` mpolacek at gcc dot gnu.org
2023-05-20  4:38 ` pinskia at gcc dot gnu.org

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