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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/64260] New: wrong code at -O1 on x86_64-linux-gnu
Date: Thu, 11 Dec 2014 00:51:00 -0000
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X-Bugzilla-Product: gcc
X-Bugzilla-Component: tree-optimization
X-Bugzilla-Version: 5.0
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=64260

            Bug ID: 64260
           Summary: wrong code at -O1 on x86_64-linux-gnu
           Product: gcc
           Version: 5.0
            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 miscompiles the following code on x86_64-linux at -O1
(only) in both 32-bit and 64-bit modes. 

This is a regression from 4.9.x. 


$ 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/5.0.0/lto-wrapper
Target: x86_64-unknown-linux-gnu
Configured with: ../gcc-trunk/configure --prefix=/usr/local/gcc-trunk
--enable-languages=c,c++ --disable-werror --enable-multilib
Thread model: posix
gcc version 5.0.0 20141210 (experimental) [trunk revision 218559] (GCC) 
$  
$ gcc-trunk -O0 small.c; a.out
$ gcc-4.9 -O1 small.c; a.out
$ 
$ gcc-trunk -O1 small.c
$ a.out
Aborted (core dumped)
$ 


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


int a = 1, b;

void
fn1 (char p)
{
  int t = 0;
  for (; b < 1; b++)
    {
      int *s = &a;
      --t && (*s &= p);
      *s &= 1;
    }
}

int
main ()
{
  fn1 (0);

  if (a != 0) 
    __builtin_abort (); 

  return 0;
}