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From: "pinskia at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug tree-optimization/101755] [12 regression] gcc.target/arm/reg_equal_test.c fails on arm since r12-2637
Date: Mon, 09 Aug 2021 21:19:36 +0000	[thread overview]
Message-ID: <bug-101755-4-eOhQkUC7PQ@http.gcc.gnu.org/bugzilla/> (raw)
In-Reply-To: <bug-101755-4@http.gcc.gnu.org/bugzilla/>

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=101755

--- Comment #2 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
  d = a | -2;
  b = (d == 0) ? c : (c % d);

d can never be 0, VRP figures this out now.
so we end up with:
d = a | -2;
b = 0xc7d24b5e % d;
if (b != 0xc7d24b5e)
  abort();

and b cannot be 0xc7d24b5e because d is negative :).

So VRP is optimizing this all the way out.

The test was trying to make sure the value 0xc7d24b5e was emitted as a
REG_EQUAL note when splitting up the constant (for the forming) in RTL.

https://gcc.gnu.org/pipermail/gcc-patches/2015-June/422430.html
https://gcc.gnu.org/pipermail/gcc-patches/2015-June/422432.html

  parent reply	other threads:[~2021-08-09 21:19 UTC|newest]

Thread overview: 8+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-08-03 15:27 [Bug tree-optimization/101755] New: " clyon at gcc dot gnu.org
2021-08-03 15:27 ` [Bug tree-optimization/101755] " clyon at gcc dot gnu.org
2021-08-09 21:02 ` amacleod at redhat dot com
2021-08-09 21:19 ` pinskia at gcc dot gnu.org [this message]
2022-03-08 14:09 ` rguenth at gcc dot gnu.org
2022-04-12 12:33 ` rearnsha at gcc dot gnu.org
2022-04-12 12:39 ` cvs-commit at gcc dot gnu.org
2022-04-12 12:41 ` rearnsha at gcc dot gnu.org

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