[Bug rtl-optimization/68376] New: wrong code at -O1 and above on x86_64-linux-gnu

[su at cs dot ucdavis.edu]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=68376

            Bug ID: 68376
           Summary: wrong code at -O1 and above on x86_64-linux-gnu
           Product: gcc
           Version: 6.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: rtl-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: su at cs dot ucdavis.edu
  Target Milestone: ---

The current gcc trunk mis-compiles the following code on x86_64-linux-gnu at
-O1 and above in both 32-bit and 64-bit modes.

It also seems to affect all earlier GCC releases since as early as 4.6.x. 


$ gcc-trunk -v
Using built-in specs.
COLLECT_GCC=gcc-trunk
COLLECT_LTO_WRAPPER=/usr/local/gcc-trunk/libexec/gcc/x86_64-pc-linux-gnu/6.0.0/lto-wrapper
Target: x86_64-pc-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 6.0.0 20151115 (experimental) [trunk revision 230395] (GCC) 
$ 
$ gcc-trunk -O0 small.c; ./a.out
$     
$ gcc-trunk -O1 small.c; ./a.out
Aborted (core dumped)
$ gcc-4.6 -O1 small.c; ./a.out
Aborted (core dumped)
$    


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


int a, b, c = 1; 
char d; 

int
main (  )
{
  for ( ; a < 1; a++ )
    for ( ; b < 1; b++ )
      {
        char e = ~d; 
        if ( d < 1 )
          e = d; 
        d = e; 
        if ( !c )
          __builtin_abort (); 
      }

  if ( d != 0 ) 
    __builtin_abort ();

  return 0;
}