From mboxrd@z Thu Jan  1 00:00:00 1970
From: Joern Rennecke <amylaar@cygnus.co.uk>
To: rth@cygnus.com
Cc: michaelh@ongaonga.chch.cri.nz, egcs@cygnus.com
Subject: Re: Autoincrement addressing modes
Date: Mon, 16 Mar 1998 20:25:00 -0000
Message-id: <199803162251.WAA08886@phal.cygnus.co.uk>
References: <19980212023505.17080@dot.cygnus.com>
X-SW-Source: 1998-03/msg00557.html

> > (define_address
> >  [(mem:SF (match_operand:SI 0 "base_register" "a"))]
> >  ""
> >  "*%0")
> 
> I think this is a swell idea.  I can see it as being particularly
> useful to use this kind of description to help auto-generate
> GO_IF_LEGITIMATE_ADDRESS and LEGITIMIZE_ADDRESS.  As it is not a
> few ports lie to gcc about how addresses really work with -fpic,
> perhaps if it were easier to describe, ports would quite lying.
> 
> Though I would get rid of the mem and add a name,
> 
> (define_address "base_disp"
>   [(plus:DI (match_operand:DI 0 "register_operand" "r")
> 	    (match_operand:DI 1 "const16_operand" "I"))]
>   ""
>   "%1(%0)")

Adding a name is fine, but I wouldn't want to drop the mem.  Note that the
mem has a mode, which is useful for a number of ports.
If it is not useful, you can still leave out the mode (i.e., it will be
VoidMODE).

moreover, we need some way to link the address forms to the places where
they are possible - e.g. it is common that the set of allowed addresses
for loads is different from the ones allowed for stores.

Should that be a list of constraints - e.g. "g" could be only for reading
general operands, "=g" only for writing general operands, "=g,g" for 
either of these, "+g" only for read-write general operands, "=" for and
kind of write-only operand...

Or should we put lists of addressing modes in some other kind of
declaration in the machine description?
E.g.:
(define_load ["base", "base_disp", "auto_inc"])
(define_store ["base", "base_disp", "auto_dec"])
(define_mem_arith ["base", "base_disp"])