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

[Ian Lance Taylor]

Andreas Schwab <schwab@suse.de> writes:

> Ian Lance Taylor <ian@wasabisystems.com> writes:
> 
> > 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.
> 
> I had the same concern, but you can disable this optimization by writing
> 0:w instead of 0.  This is in par with other kinds of optimizations that
> only happen when using unspecified size operands.

OK, I withdraw my objection.

Ian