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From: "rguenth at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug tree-optimization/113411] ABS<a>*ABS<b> can be simplified to ABS<a*b>
Date: Tue, 16 Jan 2024 08:13:01 +0000	[thread overview]
Message-ID: <bug-113411-4-kOMYC6ANft@http.gcc.gnu.org/bugzilla/> (raw)
In-Reply-To: <bug-113411-4@http.gcc.gnu.org/bugzilla/>

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=113411

Richard Biener <rguenth at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
     Ever confirmed|0                           |1
   Last reconfirmed|                            |2024-01-16
             Status|UNCONFIRMED                 |NEW

--- Comment #1 from Richard Biener <rguenth at gcc dot gnu.org> ---
I think it's OK for reals with -fno-rounding-math.

It's valid for integers with or without undefined overflow, the corner
case to consider is

  abs(-INT_MAX - 1) * abs (b)

where with undefined overflow the abs() is already invoking undefined
behavior.  The problematical multiplication is (-INT_MAX-1) * -1 but
we cannot arrive at this from a defined input.  For

  abs(a*b)

the problematical input is -INT_MAX - 1 but we can't arrive at that
either (b == 1 with a == -INT_MAX-1 is undefined, b == -1 the same).

  reply	other threads:[~2024-01-16  8:13 UTC|newest]

Thread overview: 3+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2024-01-16  0:23 [Bug tree-optimization/113411] New: " pinskia at gcc dot gnu.org
2024-01-16  8:13 ` rguenth at gcc dot gnu.org [this message]
2024-01-21  9:58 ` [Bug tree-optimization/113411] " pinskia at gcc dot gnu.org

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