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From: "gcc-bugzilla at gcc dot gnu dot org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug other/17103] New: Opportunity to replace multiply with shift/add sequence
Date: Thu, 19 Aug 2004 14:59:00 -0000	[thread overview]
Message-ID: <20040819145911.17103.steinmtz@us.ibm.com> (raw)

Description:
A non-optimal code sequence is illustraded.    Duplicate using gcc 3.5 and
command line:

gcc -O3 -m32 -c test.c


Testcase:
long foo(long x)
{
 return (x * 258);
}

Assembly:
Currently, gcc 3.5 generates the following:

foo:
      mulli 3,3,258
      blr

It would be more efficient to use a shift/add sequence:

foo:
      or 0,3,3
      rlwinm 3,3,8
      add 0,0,0
      add 3,3,0
      blr




-- 
           Summary: Opportunity to replace multiply with shift/add sequence
           Product: gcc
           Version: 3.5.0
            Status: UNCONFIRMED
          Severity: enhancement
          Priority: P1
         Component: other
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: steinmtz at us dot ibm dot com
                CC: gcc-bugs at gcc dot gnu dot org,steinmtz at us dot ibm
                    dot com
 GCC build triplet: powerpc64-linux
  GCC host triplet: powerpc64-linux
GCC target triplet: powerpc64-linux


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=17103


             reply	other threads:[~2004-08-19 14:59 UTC|newest]

Thread overview: 4+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2004-08-19 14:59 gcc-bugzilla at gcc dot gnu dot org [this message]
2004-08-19 15:34 ` [Bug middle-end/17103] " pinskia at gcc dot gnu dot org
2004-08-19 15:46 ` [Bug target/17103] " falk at debian dot org
2004-09-12 20:37 ` dje at gcc dot gnu dot org

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