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Date: Thu, 19 Aug 2004 14:59:00 -0000
From: "gcc-bugzilla at gcc dot gnu dot org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Message-ID: <20040819145911.17106.steinmtz@us.ibm.com>
Reply-To: gcc-bugzilla@gcc.gnu.org
Subject: [Bug other/17106] New: Opportunity to eliminate loads from TOC.
X-Bugzilla-Reason: CC
X-SW-Source: 2004-08/txt/msg01929.txt.bz2
List-Id: <gcc-bugs.sourceware.org>

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

gcc -O3 -m64 -c test.c


Testcase:
static int s1, s2, s3;
void no_common_toc1 ()
{

  s1 = 1;
  s2 = 2;
  s3 = 3;
}

Assembly:
The code generated by gcc 3.5 contains loads the address from the TOC for
each
target location:

.no_common_toc1:
      ld 11,.LC0@toc(2)
      li 0,1
      li 9,2
      ld 8,.LC2@toc(2)
      ld 10,.LC1@toc(2)
      stw 0,0(11)
      li 0,3
      stw 9,0(10)
      stw 0,0(8)
      blr

A single load of the base of the TOC is all that is needed:

.no_common_toc1:
      ld 11,.LC0@toc(2)
      li 0,1
      li 9,2
      stw 0,0(11)
      li 0,3
      stw 9,4(11)
      stw 0,8(11)
      blr




-- 
           Summary: Opportunity to eliminate loads from TOC.
           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=17106