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From: "jasonwucj at gmail dot com" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug c/56956] ftrapv traps on valid abs-like code
Date: Mon, 15 Apr 2013 04:18:00 -0000	[thread overview]
Message-ID: <bug-56956-4-OHPa9wpZYo@http.gcc.gnu.org/bugzilla/> (raw)
In-Reply-To: <bug-56956-4@http.gcc.gnu.org/bugzilla/>


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=56956

--- Comment #4 from Chung-Ju Wu <jasonwucj at gmail dot com> 2013-04-15 04:18:13 UTC ---
(In reply to comment #2)
> (In reply to comment #1)
> > I think 'x' can not present negative value.
> 
> The unary minus operator is defined for unsigned types. It doesn't produce
> signed overflow.

According to C99 6.5.3.3 Point 3 and C99 6.5 Point 5:

"The result of the unary '-' operator is the negative of its operand."

"... if the result is ... not in the range of representable
 values for its type... the behavior is undefined."

So my understanding is that the evaluation expression '-x' is not
a representable value of 'uint64_t', which is undefined behavior,
resulting abort if -ftrav is issued.

Perhaps my understanding is incorrect? :(


  parent reply	other threads:[~2013-04-15  4:18 UTC|newest]

Thread overview: 11+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2013-04-14 19:14 [Bug c/56956] New: " sunfish at google dot com
2013-04-15  0:58 ` [Bug c/56956] " jasonwucj at gmail dot com
2013-04-15  3:53 ` sunfish at google dot com
2013-04-15  3:54 ` sunfish at google dot com
2013-04-15  4:18 ` jasonwucj at gmail dot com [this message]
2013-04-15  5:12 ` sunfish at google dot com
2015-10-22 11:15 ` mpolacek at gcc dot gnu.org
2015-10-22 12:09 ` rguenth at gcc dot gnu.org
2015-10-28 11:20 ` [Bug middle-end/56956] " rguenth at gcc dot gnu.org
2015-10-29  8:22 ` rguenth at gcc dot gnu.org
2015-10-29  8:24 ` [Bug middle-end/56956] [4.9/5 Regression] " rguenth at gcc dot gnu.org

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