* h8300.md: Add more comments about things which seem
        wrong, stupid, or just don't make any sense yet.

        * h8300.c (adds_subs_operand): New function.
        (output_adds_subs): New function.
        * h8300.md (addhi3): Turn into a define_expand.
        (addhi3 using adds_subs): New pattern.
        (H8300 addhi): Derived from old addhi pattern.  Simplified.
        (H8300H addhi): Likewise.
        (addsi using adds_subs): New pattern.  Only used on H8300H.
        (addsi_h8300): Allow "a" registers as destination.
        (addsi_h8300h):  Simplify.  Allow "a" registers as destination.

        * h8300.md (bcs): New attribute type.
        (default_length): Compute correct length for bcs insns.
        (bcs_qiqi, bcs_hihi, bs_hiqi): Use new type and update
        to account for correct length computation.

        * h8300.md (movhi_internal): Demand at least one operand to
        be a register.
        (movsi_h8300): Optimize loading certain constants.
        (movsi_h8300h): Likewise.

        * h8300.h (NO_FUNCTION_CSE): Comment out.
        (FUNCTION_ARG_REGNO_P): Properly define for TARGET_QUICKCALL.
        (RETURN_IN_MEMORY): Don't return small structs in regs.

From-SVN: r11751