[Bug tree-optimization/59747] New: wrong code at -Os and above on x86_64-linux-gnu in 64-bit mode

[su at cs dot ucdavis.edu]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=59747

            Bug ID: 59747
           Summary: wrong code at -Os and above 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 miscompiles the following code on x86_64-linux at -Os and
above in 64-bit mode (but not 32-bit). 

This is a regression from 4.8.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/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 20140109 (experimental) [trunk revision 206472] (GCC) 
$ 
$ gcc-trunk -m64 -O1 small.c; a.out
0
$ gcc-trunk -m32 -Os small.c; a.out
0
$ gcc-4.8 -m64 -Os small.c; a.out
0
$ 
$ gcc-trunk -m64 -Os small.c; a.out
1
$ 


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


int printf (const char *, ...);

int a[6], b, c = 1, d;
short e;

void
fn1 (int p)
{
  b = a[p];
}

int
main ()
{
  a[0] = 1;
  if (c)
    e--;
  d = e;
  long long f = e;
  fn1 ((f >> 56) & 1);
  printf ("%d\n", b);
  return 0;
}