RE: Constraints between operands

["Will Newton" <will.newton@imgtec.com>]

> > [...]
> > 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.

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?