(decode_field_reference): Don't check TREE_CODE of EXP; let get_inner_reference decide if have reference.

(decode_field_reference): Don't check TREE_CODE of EXP; let
get_inner_reference decide if have reference.
Allow no bit reference if have AND_MASK.
(all_ones_mask_p): Use tree_int_cst_equal, not operand_equal_p.
(unextend): New function.
(fold_truthop): For constant cases, use new function, rework
conversion, and warn if comparison can never be true.

From-SVN: r9099