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RE: Constraints between operands
- From: Doug Evans <dje at transmeta dot com>
- To: "Will Newton" <will dot newton at imgtec dot com>
- Cc: "Frank Ch. Eigler" <fche at redhat dot com>, <cgen at sources dot redhat dot com>
- Date: Wed, 21 Sep 2005 08:39:08 -0700 (PDT)
- Subject: RE: Constraints between operands
- References: <0D107966AF6D79418315B7C5549F4B5104DFDF@lemail1.le.imgtec.org>
Will Newton writes:
>
> > > [...]
> > > I'm using cgen to write a binutils port for a processor. I've come
> > > across a problem I haven't been able to solve yet with expressing a
> > > constraint between a number of fields in an instruction.
> > > [...]
> > > ADD D0.1,D0.2 ; Data unit 0 for both regs, OK ADD D0.1,D1.2 ; Data
> > > unit mismatch, error!
> > > [...]
> >
> > One way may be to write a custom operand parser for the
> > second D slot, which would enforce this constraint. It would
> > signal a parse error.
Another alternative I've seen is to specify a special operand at the
end whose sole purpose is to validate the insn. It's at the end so it
has a view of the entire insn.
> I could not see an easy way to reference a previous field. The prototype
> of parse handlers is like:
>
> static const char *
> parse_hi16 (cd, strp, opindex, valuep)
> CGEN_CPU_DESC cd; /* CPU description */
> const char **strp; /* Current position in input
> text */
> int opindex; /* ??? */
> unsigned long *valuep; /* Result */
>
> In order to find what the previous operand's data unit was the only way
> I can see is to rewind strp and parse the input text, which may or may
> not work and seems quite nasty. Or is there an easier way?
I was going to say have either a special "parse" or "insert" handler.
I seem to recall other instances where I needed to validate two
operands against each other, but I can't find one at the moment.
At any rate, you're right, the parse handler isn't passed sufficient info.
If I can't find an existing example I think we need to extend cgen.
e.g. pass the fields struct to either or both of the parse and insert
handlers.
Comments folks?