[Bug c++/28707] New: Incorrect optimization inside member function

[Bug c++/28707] New: Incorrect optimization inside member function

[pierre at senellart dot com]

Consider the following minimal example :

--cut after--
#include<iostream>

struct A {
  long double * t;
  int n;

  A() { n=2; t=new long double[2]; }
  long double &operator()(unsigned i) {return t[i];};
  void bug();
};

void A::bug()
{
  A a;
  for(int k=0;k<n;k++) {
    if(k!=0)
      a(k-1)=0;
    a(k)=1;
  }

  if(a(0)==1)
    std::cerr << "bug" << std::endl;
}

int main()
{
  A a;
  a.bug();
  return 0;
}
--cut before--

When compiled with -O with g++ 4.0.1 or 4.0.3, "bug" is displayed, which is
incorrect. This does not happen when no optimization is performed.

Reproducible with the two following compilers (output of "g++ -v"):
Using built-in specs.
Reading specs from /usr/local/util/etc/gcc-3.4-fedora.specs
Target: i386-redhat-linux
Configured with: ../configure --prefix=/usr --mandir=/usr/share/man
--infodir=/usr/share/info --enable-shared --enable-threads=posix
--enable-checking=release --with-system-zlib --enable-__cxa_atexit
--disable-libunwind-exceptions --enable-libgcj-multifile
--enable-languages=c,c++,objc,java,f95,ada --enable-java-awt=gtk
--with-java-home=/usr/lib/jvm/java-1.4.2-gcj-1.4.2.0/jre
--host=i386-redhat-linux
Thread model: posix
gcc version 4.0.1 20050727 (Red Hat 4.0.1-5)

Using built-in specs.
Target: i486-linux-gnu
Configured with: ../src/configure -v
--enable-languages=c,c++,java,f95,objc,ada,treelang --prefix=/usr
--enable-shared --with-system-zlib --libexecdir=/usr/lib
--without-included-gettext --enable-threads=posix --enable-nls
--program-suffix=-4.0 --enable-__cxa_atexit --enable-clocale=gnu
--enable-libstdcxx-debug --enable-java-awt=gtk-default --enable-gtk-cairo
--with-java-home=/usr/lib/jvm/java-1.4.2-gcj-4.0-1.4.2.0/jre --enable-mpfr
--disable-werror --with-tune=pentium4 --enable-checking=release i486-linux-gnu
Thread model: posix
gcc version 4.0.3 (Ubuntu 4.0.3-1ubuntu5)

Not reproducible with g++ 3.5 on i486-linux.

This bug also disappears when long double is replaced with double.


-- 
           Summary: Incorrect optimization inside member function
           Product: gcc
           Version: 4.0.3
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: pierre at senellart dot com


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=28707

[Bug c++/28707] [4.0 Regression] Incorrect optimization inside member function

[pinskia at gcc dot gnu dot org]

------- Comment #1 from pinskia at gcc dot gnu dot org  2006-08-13 15:15 -------
Only a 4.0.x regression.  DSE removes the store for some reason.


-- 

pinskia at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |law at gcc dot gnu dot org
           Keywords|                            |wrong-code
      Known to fail|                            |4.0.3
      Known to work|                            |4.1.0 3.4.0
            Summary|Incorrect optimization      |[4.0 Regression] Incorrect
                   |inside member function      |optimization inside member
                   |                            |function
   Target Milestone|---                         |4.0.4


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=28707

[Bug tree-optimization/28707] [4.0 Regression] Incorrect optimization inside member function

[law at redhat dot com]

------- Comment #2 from law at redhat dot com  2006-08-14 07:39 -------
Created an attachment (id=12073)
 --> (http://gcc.gnu.org/bugzilla/attachment.cgi?id=12073&action=view)
Backport of patch to GCC 4.0 branch (not thoroughly tested)

This bug was fixed long ago (prior to branching for GCC 4.1).  However, the fix
was never backported to the GCC 4.0 branch.  Attached is a lightly tested
backport of the patch.

Given the age of GCC 4.0 and my priorities, I'm not planning to run this
through the testing process necessary to get it included in GCC 4.0.x  The GCC
4.0.x release manager (or anyone else for that matter) is welcome to run
through the proper procedures to get this patch included.  Credit for the fix
should go to Daniel Jacobowitz. 


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=28707

[Bug tree-optimization/28707] [4.0 Regression] Incorrect optimization inside member function

[pinskia at gcc dot gnu dot org]

-- 

pinskia at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |NEW
     Ever Confirmed|0                           |1
   Last reconfirmed|0000-00-00 00:00:00         |2006-08-16 05:40:07
               date|                            |


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=28707

[Bug tree-optimization/28707] [4.0 Regression] Incorrect optimization inside member function

[gdr at gcc dot gnu dot org]

------- Comment #3 from gdr at gcc dot gnu dot org  2007-02-03 18:52 -------
Fixed in GCC-4.1.0.
Won't fix for GCC-4.0.x.


-- 

gdr at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |RESOLVED
         Resolution|                            |WONTFIX


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=28707