[Bug tree-optimization/68013] New: ICE on valid code at -O2 on x86_64-linux-gnu in duplicate_thread_path, at tree-ssa-threadupdate.c:2469

["su at cs dot ucdavis.edu" <gcc-bugzilla at gcc dot gnu dot org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=68013

            Bug ID: 68013
           Summary: ICE on valid code at -O2 on x86_64-linux-gnu in
                    duplicate_thread_path, at tree-ssa-threadupdate.c:2469
           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 on x86_64-linux-gnu in both 32-bit and 64-bit modes.

It is a regression from 5.2.x.


$ gcc-trunk -v
Using built-in specs.
COLLECT_GCC=gcc-trunk
COLLECT_LTO_WRAPPER=/usr/local/gcc-trunk/libexec/gcc/x86_64-pc-linux-gnu/6.0.0/lto-wrapper
Target: x86_64-pc-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 20151018 (experimental) [trunk revision 228953] (GCC) 
$ 
$ gcc-trunk -Os -c small.c
$ gcc-5.2 -O2 -c small.c
$ 
$ gcc-trunk -O2 -c small.c
small.c: In function âfn1â:
small.c:4:1: internal compiler error: in duplicate_thread_path, at
tree-ssa-threadupdate.c:2469
 fn1 ()
 ^
0xcd3440 duplicate_thread_path
        ../../gcc-trunk/gcc/tree-ssa-threadupdate.c:2468
0xcd3440 thread_through_all_blocks(bool)
        ../../gcc-trunk/gcc/tree-ssa-threadupdate.c:2669
0xc0a203 execute
        ../../gcc-trunk/gcc/tree-ssa-dom.c:622
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, d, e, f;

void
fn1 ()
{
  for (; e;)
    {
      e = f;
      for (; b;)
        {
          b = a;
          f = a || d ? 0 : c;
        }
      d = 0;
    }
}