[Bug tree-optimization/63898] [5 Regression] r217560 caused segfault building 462.libquantum from cpu2006

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=63898

--- Comment #5 from Richard Biener <rguenth at gcc dot gnu.org> ---
Ok, so this is the missing effect of

    case RDIV_EXPR:
      /* Don't touch a floating-point divide by zero unless the mode
         of the constant can represent infinity.  */
      if (TREE_CODE (arg1) == REAL_CST
          && !MODE_HAS_INFINITIES (TYPE_MODE (TREE_TYPE (arg1)))
          && real_zerop (arg1))
        return NULL_TREE;