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Date: Thu, 01 Sep 2005 02:04:00 -0000
From: "pinskia at gcc dot gnu dot org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Message-ID: <20050901020344.23669.pinskia@gcc.gnu.org>
Reply-To: gcc-bugzilla@gcc.gnu.org
Subject: [Bug middle-end/23669] New: fold does convert (-a)/10 into a/-10.
X-Bugzilla-Reason: CC
X-SW-Source: 2005-09/txt/msg00019.txt.bz2
List-Id: <gcc-bugs.sourceware.org>

Another idea from LLVM.
The following two functions should be the same asm:
int f(int a)
{
  return (-a)/10;
}
int f1(int a)
{
  return a/-10;
}

----
We currently get on PPC:
_f:
        lis r0,0x6666
        neg r3,r3
        ori r0,r0,26215
        mulhw r0,r3,r0
        srawi r3,r3,31
        srawi r0,r0,2
        subf r3,r3,r0
        blr
_f1:
        lis r0,0x6666
        ori r0,r0,26215
        mulhw r0,r3,r0
        srawi r3,r3,31
        srawi r0,r0,2
        subf r3,r0,r3
        blr

As you can see f1 has one less instruction which should be better.

-- 
           Summary: fold does convert (-a)/10 into a/-10.
           Product: gcc
           Version: 4.1.0
            Status: UNCONFIRMED
          Keywords: missed-optimization
          Severity: normal
          Priority: P2
         Component: middle-end
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: pinskia at gcc dot gnu dot org
                CC: gcc-bugs at gcc dot gnu dot org
OtherBugsDependingO 19987
             nThis:


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=23669