The following code causes an ICE when compiled with the current gcc trunk at -O2 and -O3 on x86_64-linux-gnu in 64-bit mode (but not in 32-bit mode). 

It 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 20131204 (experimental) [trunk revision 205660] (GCC) 
$ 
$ gcc-trunk -m64 -Os -c small.c       
$ gcc-4.8 -m64 -O2 -c small.c
$ gcc-trunk -m32 -O2 -c small.c
$ 
$ gcc-trunk -m64 -O2 -c small.c
small.c: In function ‘fn2’:
small.c:31:1: error: incorrect sharing of tree nodes
 }
 ^
a.f2
# .MEM_11 = VDEF <.MEM_10>
a.f2 = D.1782;
small.c:31:1: internal compiler error: verify_gimple failed
0x9d3821 verify_gimple_in_cfg(function*)
	../../gcc-trunk/gcc/tree-cfg.c:4848
0x8fa874 execute_function_todo
	../../gcc-trunk/gcc/passes.c:1843
0x8fb273 execute_todo
	../../gcc-trunk/gcc/passes.c:1877
Please submit a full bug report,
with preprocessed source if appropriate.
Please include the complete backtrace with any bug report.
See <http://gcc.gnu.org/bugs.html> for instructions.
$ 


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


struct S0
{
  int f0;
};

struct S1
{
  int f1;
  struct S0 f2;
} c;

int b;

struct S0
fn1 ()
{
  struct S1 d;
  if (b) 
    for (; c.f1;)
      ;
  else
    return d.f2; 
}

struct S0
fn2 ()
{
  struct S1 a;
  a.f2 = fn1 ();
  return a.f2; 
}