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From: "agner at agner dot org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug c/49820] Explicit check for integer negative after abs optimized away
Date: Mon, 25 Jul 2011 14:22:00 -0000	[thread overview]
Message-ID: <bug-49820-4-JAtIPXspNb@http.gcc.gnu.org/bugzilla/> (raw)
In-Reply-To: <bug-49820-4@http.gcc.gnu.org/bugzilla/>

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=49820

--- Comment #12 from Agner Fog <agner at agner dot org> 2011-07-25 14:21:52 UTC ---
No the behavior is not predictable when it sometimes warns about ignoring
overflow, and sometimes not. Please add a warning when it optimizes away an
overflow check after the abs function.

Unsafe optimizations are sometimes good, sometimes causing hard-to-find bugs.
The programmer can't always predict what kind of optimizations the compiler
makes. A warning feature is the best way to enable the programmer to check if
the compiler does the right thing. The programmer can then turn off specific
warnings after verifying that the optimizations are OK.


  parent reply	other threads:[~2011-07-25 14:22 UTC|newest]

Thread overview: 16+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2011-07-23  7:11 [Bug c/49820] New: " agner at agner dot org
2011-07-23  7:20 ` [Bug c/49820] " schwab@linux-m68k.org
2011-07-23 17:23 ` pinskia at gcc dot gnu.org
2011-07-23 17:30 ` schwab@linux-m68k.org
2011-07-23 20:48 ` noloader at gmail dot com
2011-07-23 20:59 ` ebotcazou at gcc dot gnu.org
2011-07-23 22:28 ` noloader at gmail dot com
2011-07-24  8:10 ` ebotcazou at gcc dot gnu.org
2011-07-24  8:17 ` agner at agner dot org
2011-07-24  9:41 ` pinskia at gcc dot gnu.org
2011-07-25  7:44 ` agner at agner dot org
2011-07-25  7:46 ` ebotcazou at gcc dot gnu.org
2011-07-25 14:22 ` agner at agner dot org [this message]
2011-07-26 19:32 ` agner at agner dot org
2011-07-27 11:23 ` ebotcazou at gcc dot gnu.org
2011-07-27 14:28 ` agner at agner dot org

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