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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/52631] New: VN does not use simplified expression for lookup
Date: Tue, 20 Mar 2012 06:09:00 -0000	[thread overview]
Message-ID: <bug-52631-4@http.gcc.gnu.org/bugzilla/> (raw)

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=52631

             Bug #: 52631
           Summary: VN does not use simplified expression for lookup
    Classification: Unclassified
           Product: gcc
           Version: 4.7.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: tree-optimization
        AssignedTo: unassigned@gcc.gnu.org
        ReportedBy: pinskia@gcc.gnu.org


Take:
unsigned f(unsigned a)
{
  unsigned b = a >> 31;
  return b&1;
}

--- CUT ---
Even though we have a simplified expression of a>>31 for b, VN does not use it.
SCC consists of: a_1(D)
Setting value number of a_1(D) to a_1(D)
SCC consists of: b_2
Value numbering b_2 stmt = b_2 = a_1(D) >> 31;
Setting value number of b_2 to b_2 (changed)
SCC consists of: D.1708_3
Value numbering D.1708_3 stmt = D.1708_3 = b_2 & 1;
RHS b_2 & 1 simplified to a_1(D) >> 31 has constants 1
Setting value number of D.1708_3 to D.1708_3 (changed)

This is a regression from 4.3.


             reply	other threads:[~2012-03-20  6:08 UTC|newest]

Thread overview: 13+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2012-03-20  6:09 pinskia at gcc dot gnu.org [this message]
2012-03-20  6:58 ` [Bug tree-optimization/52631] [4.6/4.7/4.8 Regression] " pinskia at gcc dot gnu.org
2012-03-20  7:34 ` pinskia at gcc dot gnu.org
2012-03-20 11:20 ` rguenth at gcc dot gnu.org
2012-03-21  0:30 ` pinskia at gcc dot gnu.org
2012-03-24  3:21 ` pinskia at gcc dot gnu.org
2012-03-24  5:06 ` pinskia at gcc dot gnu.org
2012-04-13 13:10 ` rguenth at gcc dot gnu.org
2012-06-14  8:21 ` rguenth at gcc dot gnu.org
2012-09-20 10:18 ` jakub at gcc dot gnu.org
2013-01-20  5:01 ` law at gcc dot gnu.org
2013-01-20  5:02 ` law at redhat dot com
2013-03-04 11:13 ` gjl at gcc dot gnu.org

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