* doc/md.texi: Document define_subst.

    * doc/md.texi: Document define_subst.
        * gensupport.c (MAX_OPERANDS): New define.
        (operand_data): New.
        (match_operand_entries_in_pattern): New.
        (used_operands_numbers): New.
        (subst_true): New.
        (subst_false): New.
        (define_subst_queue): New.
        (define_subst_tail): New.
        (define_subst_attr_queue): New.
        (define_subst_attr_tail): New.
        (has_subst_attribute): New.
        (subst_pattern_match): New.
        (get_alternatives_number): New.
        (alter_output_for_subst_insn): New.
        (alter_attrs_for_subst_insn): New.
        (process_substs_on_one_elem): New.
        (subst_dup): New.
        (process_define_subst): New.
        (duplicate_alternatives): New.
        (duplicate_each_alternative): New.
        (constraints_handler_t): New typedef.
        (alter_constraints): New.
        (adjust_operands_numbers): New.
        (replace_duplicating_operands_in_pattern): New.
        (remove_from_queue): New.
        (process_rtx): Handle define_subst and define_subst_attr.
        (change_subst_attribute): New.
        (alter_predicate_for_insn): Fix formatting.
        (alter_attrs_for_insn): Likewise.
        (alter_output_for_insn): Likewise.
        (mark_operands_from_match_dup): New.
        (mark_operands_used_in_match_dup): New.
        (find_first_unused_number_of_operand): New.
        (renumerate_operands_in_pattern): New.
        (generate_match_dup): New.
        (check_define_attr_duplicates): New.
        (init_rtx_reader_args_cb): Add checking for duplicated attrs and
        processing of define_subst.
        (read_md_rtx): Handle define_subst.
        * read-rtl.c (struct subst_attr_to_iter_mapping): New.
        (substs): New global.
        (apply_subst_iterator): New.
        (bind_subst_iter_and_attr): New.
        (find_subst_iter_by_attr): New.
        (map_attr_string): Handle subst-iterators.
        (add_condition_to_rtx): Handle define_subst.
        (apply_iterators): Likewise.
        (initialize_iterators): Likewise.
        (add_define_attr_for_define_subst): New.
        (add_define_subst_attr): New.
        (read_subst_mapping): New.
        (read_rtx): Handle define_subst_attr.
        (read_rtx_code): Add subst-attributes recognition during reading of
        strings.
        * rtl.def (DEFINE_EXPAND): Add vector of attributes.
        (DEFINE_SUBST): New.
        (DEFINE_SUBST_ATTR): New.

git-svn-id: svn+ssh://gcc.gnu.org/svn/gcc/trunk@193618 138bc75d-0d04-0410-961f-82ee72b054a4