[Bug c/60578] New: wrong code (that hangs) at -O0 on x86_64-linux-gnu (affecting all gcc versions)

[su at cs dot ucdavis.edu]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=60578

            Bug ID: 60578
           Summary: wrong code (that hangs) at -O0 on x86_64-linux-gnu
                    (affecting all gcc versions)
           Product: gcc
           Version: 4.9.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c
          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 -O0 in
64-bit mode (but not 32-bit). 

It affects all GCC versions and seems to do with wrong integer promotion in the
expression "(c ^ 0L) < -1". 

$ 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 --prefix=/usr/local/gcc-trunk
--enable-languages=c,c++ --disable-werror --enable-multilib
Thread model: posix
gcc version 4.9.0 20140318 (experimental) [trunk revision 208631] (GCC)
$
$ gcc-trunk -m32 -O0 small.c
$ a.out
$ gcc-trunk -m64 -O1 small.c
$ a.out
$
$ gcc-trunk -m64 -O0 small.c
$ a.out
^C
$


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


int a, *b = &a;

unsigned c;

int
foo ()
{ 
  return 0;
}

int
bar ()
{ 
  int i, j, m, n;
  *b = foo ();
  for (i = 0; i;)
    for (; j;)
      m = 0;
  if ((c ^ 0L) < -1)
    return 0;
  for (; n;)
    ;
  return 0;
}

int
main ()
{ 
  bar ();
  return 0;
}