[Bug tree-optimization/66949] New: ICE at -O2 and -O3 on x86_64-linux-gnu in tree_ssa_phiopt_worker, at tree-ssa-phiopt.c:335

[su at cs dot ucdavis.edu]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=66949

            Bug ID: 66949
           Summary: ICE at -O2 and -O3 on x86_64-linux-gnu in
                    tree_ssa_phiopt_worker, at tree-ssa-phiopt.c:335
           Product: gcc
           Version: 6.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: tree-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: su at cs dot ucdavis.edu
  Target Milestone: ---

The following code causes an ICE when compiled with the current gcc trunk at
-O2 and -O3 on x86_64-linux-gnu in both 32-bit and 64-bit modes. 

It is a regression from 5.1.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/6.0.0/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 6.0.0 20150719 (experimental) [trunk revision 225987] (GCC) 
$ 
$ gcc-trunk -Os small.c; ./a.out
$ gcc-5.1 -O2 small.c; ./a.out
$ 
$ gcc-trunk -O2 small.c
small.c: In function ‘fn2’:
small.c:10:1: internal compiler error: in tree_ssa_phiopt_worker, at
tree-ssa-phiopt.c:335
 fn2 ()
 ^
0xcf3dfd tree_ssa_phiopt_worker
        ../../gcc-trunk/gcc/tree-ssa-phiopt.c:335
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.
$ 


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


int a, *b = &a, c;

unsigned short
fn1 (unsigned short p1, unsigned int p2)
{
  return p2 > 1 || p1 >> p2 ? p1 : p1 << p2;
}

void
fn2 ()
{
  int *d = &a;
  for (a = 0; a < -1; a = 1)
    ;
  if (a < 0)
    c = 0; 
  *b = fn1 (*d || c, *d);
}

int
main ()
{
  fn2 (); 
  return 0;
}