optimization/5264: Possible optimization bug at -O2 on HP-UX

optimization/5264: Possible optimization bug at -O2 on HP-UX

[luke]

>Number:         5264
>Category:       optimization
>Synopsis:       Possible optimization bug at -O2 on HP-UX
>Confidential:   no
>Severity:       serious
>Priority:       medium
>Responsible:    unassigned
>State:          open
>Class:          wrong-code
>Submitter-Id:   net
>Arrival-Date:   Thu Jan 03 07:06:00 PST 2002
>Closed-Date:
>Last-Modified:
>Originator:     Luke Tierney
>Release:        gcc version 2.95.2 19991024 (release)
>Organization:
>Environment:
HP-UX bass B.11.00 A 9000/780 2007851940
>Description:
A possible optimization bug at -O2 on HP-UX found in building
R (Gnu S).  Simplified program:
 ---------------(opttest.c)--------------------------------------------#include <stdio.h>

double x[] = { 1.0, 2.0}, y[] = { 1.0, 2.0 }, z[2];

main()
{
  int i, i1, i2, n, n1, n2;

  i1 = i2 = 0;
  n = n1 = n2 = 2;

  for (i = 0; i < n; i++) {
    z[i] = x[i1] + y[i2];
    i1 = (++i1 == n1) ? 0 : i1;
    i2 = (++i2 == n2) ? 0 : i2;
  }
  printf("z[1] = %g\n", z[1]);
}
----------------------------------------------------------------------

Without optimization or with just -O it works fine:

tierney@bass [125]% gcc -o opttest opttest.c
ltierney@bass [126]% ./opttest 
z[1] = 4ltierney@bass [127]% gcc -O -o opttest opttest.c
ltierney@bass [128]% ./opttest
z[1] = 4

But with -O2 it gets the wrong answer:

ltierney@bass [129]% gcc -O2 -o opttest opttest.c
ltierney@bass [130]% ./opttest
z[1] = 2

Please let me know if you need additional info.


>How-To-Repeat:
On HP-UX compare output of

gcc -O2 -o opttest opttest.c; ./opttest
gcc -O -o opttest opttest.c; ./opttest
>Fix:

>Release-Note:
>Audit-Trail:
>Unformatted:
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Re: optimization/5264: Possible optimization bug at -O2 on HP-UX

[rodrigc]

Synopsis: Possible optimization bug at -O2 on HP-UX

State-Changed-From-To: feedback->closed
State-Changed-By: rodrigc
State-Changed-When: Fri Jan  4 10:07:41 2002
State-Changed-Why:
    Submitter reports that problem does not occur in 2.95.3 or
    3.0.3

http://gcc.gnu.org/cgi-bin/gnatsweb.pl?cmd=view%20audit-trail&database=gcc&pr=5264

Re: optimization/5264: Possible optimization bug at -O2 on HP-UX

[Luke Tierney]

The following reply was made to PR optimization/5264; it has been noted by GNATS.

From: Luke Tierney <luke@stat.umn.edu>
To: rodrigc@gcc.gnu.org, gcc-bugs@gcc.gnu.org, gcc-prs@gcc.gnu.org,
   luke@muskrat.stat.umn.edu, nobody@gcc.gnu.org, gcc-gnats@gcc.gnu.org
Cc:  
Subject: Re: optimization/5264: Possible optimization bug at -O2 on HP-UX
Date: Fri, 4 Jan 2002 11:29:57 -0600

 The patch applied to 2.95.2 does not help.  But the example no longer
 occurs in 2.95.3 or 3.0.3 (both without patching).
 
 luke
 
 
 On Thu, Jan 03, 2002 at 04:03:58PM -0000, rodrigc@gcc.gnu.org wrote:
 > Synopsis: Possible optimization bug at -O2 on HP-UX
 > 
 > State-Changed-From-To: open->feedback
 > State-Changed-By: rodrigc
 > State-Changed-When: Thu Jan  3 08:03:57 2002
 > State-Changed-Why:
 >     Can you try applying the patch mentioned at the bottom of
 >     the message at:
 >     http://gcc.gnu.org/ml/gcc-patches/2001-12/msg02298.html
 > 
 > http://gcc.gnu.org/cgi-bin/gnatsweb.pl?cmd=view%20audit-trail&database=gcc&pr=5264
 
 -- 
 Luke Tierney
 University of Minnesota                      Phone:           612-625-7843
 School of Statistics                         Fax:             612-624-8868
 313 Ford Hall, 224 Church St. S.E.           email:      luke@stat.umn.edu
 Minneapolis, MN 55455 USA                    WWW:  http://www.stat.umn.edu

Re: optimization/5264: Possible optimization bug at -O2 on HP-UX

[rodrigc]

Synopsis: Possible optimization bug at -O2 on HP-UX

State-Changed-From-To: open->feedback
State-Changed-By: rodrigc
State-Changed-When: Thu Jan  3 08:03:57 2002
State-Changed-Why:
    Can you try applying the patch mentioned at the bottom of
    the message at:
    http://gcc.gnu.org/ml/gcc-patches/2001-12/msg02298.html

http://gcc.gnu.org/cgi-bin/gnatsweb.pl?cmd=view%20audit-trail&database=gcc&pr=5264