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From: "su at cs dot ucdavis.edu" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug tree-optimization/58831] New: wrong code at -O2 and -O3 on x86_64-linux-gnu in 64-bit mode
Date: Mon, 21 Oct 2013 23:05:00 -0000
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X-Bugzilla-Type: new
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X-Bugzilla-Product: gcc
X-Bugzilla-Component: tree-optimization
X-Bugzilla-Version: 4.9.0
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X-Bugzilla-Severity: normal
X-Bugzilla-Who: su at cs dot ucdavis.edu
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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=58831

            Bug ID: 58831
           Summary: wrong code at -O2 and -O3 on x86_64-linux-gnu in
                    64-bit mode
           Product: gcc
           Version: 4.9.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: tree-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: su at cs dot ucdavis.edu

The current gcc trunk and 4.8.x miscompiles the following code on x86_64-linux
at -O2 and -O3 in 64-bit mode. 

This is a regression from 4.7.x. 

I had hoped to reduce it even further, but it's the best I have so far. 

$ gcc-trunk -v
Using built-in specs.
COLLECT_GCC=gcc-trunk
COLLECT_LTO_WRAPPER=/usr/local/gcc-trunk/libexec/gcc/x86_64-unknown-linux-gnu/4.9.0/lto-wrapper
Target: x86_64-unknown-linux-gnu
Configured with: ../gcc-trunk/configure
--enable-languages=c,c++,objc,obj-c++,fortran,lto --disable-werror
--enable-checking=release --with-gmp=/usr/local/gcc-trunk
--with-mpfr=/usr/local/gcc-trunk --with-mpc=/usr/local/gcc-trunk
--with-cloog=/usr/local/gcc-trunk --prefix=/usr/local/gcc-trunk
Thread model: posix
gcc version 4.9.0 20131021 (experimental) [trunk revision 203907] (GCC) 
$ 
$ gcc-trunk -m64 -O1 small.c; a.out
$ gcc-trunk -m32 -O2 small.c; a.out
$ gcc-4.7.3 -m64 -O2 small.c; a.out
$ 
$ gcc-trunk -m64 -O2 small.c; a.out
a.out: small.c:14: fn1: Assertion `r' failed.
Aborted (core dumped)
$ gcc-trunk -m64 -O3 small.c; a.out
a.out: small.c:14: fn1: Assertion `r' failed.
Aborted (core dumped)
$ 
$ gcc-4.8.2 -m64 -O2 small.c; a.out
a.out: small.c:14: fn1: Assertion `r' failed.
Aborted (core dumped)
$ gcc-4.8.2 -m64 -O3 small.c; a.out
a.out: small.c:14: fn1: Assertion `r' failed.
Aborted (core dumped)
$ 


--------------------------------


#include<assert.h>

int a, *b, c, d, f, **i, p, q, *r;
short o, j;

static int
fn1 (int *p1, int **p2)
{
  int **e = &b;
  for (; p; p++)
    *p1 = 1;
  *e = *p2 = &d;

  assert(r); 

  return c;
}

static int **
fn2 ()
{
  for (f = 0; f != 42; f++)
    {
      int *g[3] = {0, 0, 0};
      for (o = 0; o; o--)
    for (; a > 1;)
      {
        int **h[1] = { &g[2] };
      }
    }
  return &r;
}



static short
fn3 ()
{
  for (; q < 1;)
    return 0;
  fn2 ();
  fn1 (0, 0);
  return 0;
}

int
main ()
{
  i = fn2 ();
  j = fn1 (b, i);
  fn3 ();
  return 0;
}