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Re: Autoincrement addressing modes
- To: law at cygnus dot com
- Subject: Re: Autoincrement addressing modes
- From: "Michael P. Hayes" <michaelh at ongaonga dot chch dot cri dot nz>
- Date: Thu, 12 Feb 1998 13:14:52 +1300
- Cc: Joern Rennecke <amylaar at cygnus dot co dot uk>, michaelh at ongaonga dot chch dot cri dot nz (Michael P. Hayes), gcc2 at cygnus dot com, egcs at cygnus dot com
- References: <199802112304.XAA11969@phal.cygnus.co.uk><20314.887238827@hurl.cygnus.com>
Jeffrey A Law writes:
>
> In message <199802112304.XAA11969@phal.cygnus.co.uk>you write:
> > > At this stage I'm interested in what other common forms should be
> > > supported.
> >
> > The SH doesn't have any exotic update forms, but it has another
> > quirk in autoincrement that gcc doesn't handle efficiently:
> > POST_INC is only available for reading, while PRE_DEC is only
> > available for writing.
> The PA has similar constraints.
Does this asymmetry only apply to these update forms of addressing
modes?
Any ideas how to describe this to GCC? I suppose if there was a flag
to differentiate memory reads from writes, then
GO_IF_LEGITIMATE_ADDRESS could reject the invalid forms.