Re: [PATCH] Fix devirtualization ICE (PR tree-optimization/59622)

[Jan Hubicka]

Hi,
this is C version
static int (*p) (int a) = (int (*)(int))__builtin_unreachable;
main()
{
  return p(1);
}

Here we get in CCP:
Folding statement: return _4;
Not folded
Folding statement: _4 = p.0_2 (1);
Folded into: _4 = __builtin_unreachable (1);

Removing dead stmt p.0_2 = __builtin_unreachable;

Removing basic block 3
<bb 3>:
return _4;


main ()
{ 
  <bb 2>:
  __builtin_unreachable (1);

}

So fold seems to do the same, but tree-ssa-propagate promptly fixes it up
          /* No point propagating into a stmt whose result is not used,
             but instead we might be able to remove a trivially dead stmt.
             Don't do this when called from VRP, since the SSA_NAME which
             is going to be released could be still referenced in VRP
             ranges.  */
          if (do_dce
              && gimple_get_lhs (stmt)
              && TREE_CODE (gimple_get_lhs (stmt)) == SSA_NAME
              && has_zero_uses (gimple_get_lhs (stmt))
              && !stmt_could_throw_p (stmt)
              && !gimple_has_side_effects (stmt))
            { 
              gimple_stmt_iterator i2;

              if (dump_file && dump_flags & TDF_DETAILS)
                { 
                  fprintf (dump_file, "Removing dead stmt ");
                  print_gimple_stmt (dump_file, stmt, 0, 0);
                  fprintf (dump_file, "\n");
                }

so we do not trigger same ICE, but I think it is more luck than
design?

Honza