[Bug rtl-optimization/83512] [8 Regression] ICE: in df_compact_blocks, at df-core.c:1729 with -freorder-blocks-algorithm=simple

[asolokha at gmx dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=83512

--- Comment #1 from Arseny Solokha <asolokha at gmx dot com> ---
I've finally cloned PR82881 as I apparently don't have permissions to reopen
that PR. I'm also adding another similar testcase for the case:

int u3;

int
w7 (int *a9)
{
  for (;;)
    {
      for (*a9 = 0; *a9 < 1; *a9++)
        {
        }

      ++u3;
    }
}

% gcc-8.0.0-alpha20171217 -O2 -freorder-blocks-algorithm=simple -c mvsp6303.c 
during RTL pass: bbro
mvsp6303.c: In function 'w7':
mvsp6303.c:14:1: internal compiler error: in df_compact_blocks, at
df-core.c:1729
 }
 ^
0x5d7389 df_compact_blocks()
       
/var/tmp/portage/sys-devel/gcc-8.0.0_alpha20171217/work/gcc-8-20171217/gcc/df-core.c:1729
0x13acd65 compact_blocks()
       
/var/tmp/portage/sys-devel/gcc-8.0.0_alpha20171217/work/gcc-8-20171217/gcc/cfg.c:160
0x13a3f08 reorder_basic_blocks
       
/var/tmp/portage/sys-devel/gcc-8.0.0_alpha20171217/work/gcc-8-20171217/gcc/bb-reorder.c:2480
0x13a3f08 execute
       
/var/tmp/portage/sys-devel/gcc-8.0.0_alpha20171217/work/gcc-8-20171217/gcc/bb-reorder.c:2570

(as of r255766)