[Bug ipa/66793] New: ICE at -Os and above on x86_64-linux-gnu (verify_flow_info failed)

[su at cs dot ucdavis.edu]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=66793

            Bug ID: 66793
           Summary: ICE at -Os and above on x86_64-linux-gnu
                    (verify_flow_info failed)
           Product: gcc
           Version: 6.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: ipa
          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
-Os and above 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 20150707 (experimental) [trunk revision 225501] (GCC) 
$ 
$ gcc-trunk -O1 small.c
$ gcc-5.1 -Os small.c
$ 
$ gcc-trunk -Os small.c
small.c: In function ‘main’:
small.c:18:1: error: control flow in the middle of basic block 2
 main ()
 ^
small.c:18:1: internal compiler error: verify_flow_info failed
0x6fa932 verify_flow_info()
        ../../gcc-trunk/gcc/cfghooks.c:268
0xbfac91 cleanup_tree_cfg_noloop
        ../../gcc-trunk/gcc/tree-cfgcleanup.c:751
0xbfac91 cleanup_tree_cfg()
        ../../gcc-trunk/gcc/tree-cfgcleanup.c:800
0xaeeb84 execute_function_todo
        ../../gcc-trunk/gcc/passes.c:1910
0xaef433 execute_todo
        ../../gcc-trunk/gcc/passes.c:2014
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, c; 

struct S0
{
  int f1;
} *d; 

void
fn1 (struct S0 p)
{
  for (p.f1 = 0; p.f1 < 1; p.f1++)
    c = a && b ? a && b : 1; 
  for (; c;)
    ;
}

int
main ()
{
  struct S0 **f = &d;
  d = 0; 
  fn1 (**f); 
  return 0;
}