[Bug tree-optimization/68240] New: compilation hangs on valid code at -O1 and above on x86_64-linux-gnu

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

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=68240

            Bug ID: 68240
           Summary: compilation hangs on valid code at -O1 and above on
                    x86_64-linux-gnu
           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 the current gcc trunk to hang at -O1 and above on
x86_64-linux-gnu in both 32-bit and 64-bit modes. 

This 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 20151105 (experimental) [trunk revision 229809] (GCC) 
$ 
$ gcc-trunk -O0 -c small.c
$ gcc-5.2 -O1 -c small.c
$ 
$ timeout -s 9 60 gcc-trunk -O1 -c small.c
Killed
$ 


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


int a, b, f;

void
fn1 ()
{
  int c = 1, d, e = 1;
  a = 1; 
  for (; f;)
    b = (c && (d = (e && a)));
}