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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: <20040819145911.17102.steinmtz@us.ibm.com>
Reply-To: gcc-bugzilla@gcc.gnu.org
Subject: [Bug other/17102] New: Missed constant folding opportunity
X-Bugzilla-Reason: CC
X-SW-Source: 2004-08/txt/msg01935.txt.bz2
List-Id: <gcc-bugs.sourceware.org>

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

gcc -O3 -m64 -c test.c


Testcase:
#include "stdio.h"
const int C0 = 0;
const int C1 = 1;
const int C2 = 2;

void bar () {
  printf("bar\n");
}

void foo ()
{
  /* GCC is able to figure this one out, do constant
     folding and dead code elimination, and eliminate
     the entire block of code */
  if (1, 2, 0) bar ();

  /* .. it unsuccessfully resolves this one. */
  if (C1, C2, C0) bar ();
}

Assembly:
.foo:
      mflr 0
      ld 9,.LC2@toc(2)
      std 0,16(1)
      lwz 0,0(9)
      stdu 1,-112(1)
      cmpwi 7,0,0
      bne- 7,.L6
      addi 1,1,112
      ld 0,16(1)
      mtlr 0
      blr
.L6:
      ld 3,.LC3@toc(2)
      bl .puts
      nop
      addi 1,1,112
      ld 0,16(1)
      mtlr 0
      blr



-- 
           Summary: Missed constant folding opportunity
           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=17102