The simplify_and_fold engine uses the EDGE_EXECUTABLE flag to eliminate 
branches:

substitute_and_fold_dom_walker::before_dom_children:

      if (gimple_code (stmt) == GIMPLE_COND)
         {
           if ((EDGE_SUCC (bb, 0)->flags & EDGE_EXECUTABLE)
               ^ (EDGE_SUCC (bb, 1)->flags & EDGE_EXECUTABLE))

... but if certain passes before VRP2 are turned off, the flag can be in 
an uninitialized state upon entry to VRP2.  This patch simply always 
sets EDGE_EXECUTABLE on all edges before invoking ranger and the S&F engine.

Bootstraps on  x86_64-pc-linux-gnu with no regressions.

OK for trunk?

Andrew