[m68k]: convert mode 5 addressing w/zero offset into mode2

[Ian Lance Taylor]

Peter Barada <peter@the-baradas.com> writes:

> This following patch converts:
> 
>      <op> 0(%Ay),%Rx
>      <op> %Ry,0(%Ax)
>      <op> 0(%Ay),0(%Ax)
> 
> into:
> 
>      <op> (%Ay),%Rx
>      <op> %Ry,(%Ax)
>      <op> (%Ay),(%Ax)
> 
> To reduce the size of the instruction by the word used to hold the
> offset.

This kind of patch makes me nervous.  Sometimes people write assembler
code with the full intention of generating a specific addressing mode,
even if it is apparently less efficient.  I'm not sure it is
appropriate for the assembler to second-guess the programmer in a case
like this.

Ian