Re: Require some enhancement in CGEN for decoder of disassember

["Frank Ch. Eigler" <fche@redhat.com>]

Hi -

On Thu, Nov 21, 2002 at 11:59:13AM +0800, Jie Zhang wrote:
> I encounter a problem when I'm using CGEN to port binutils.
> In my target, there is a rather strange 4-bit field.
> There are two insns, A and B. This field is operand in insn A,
> but opcode for insn B.
> [...]
> In insn A, the value of the operand can range from 0 through 14.
> If this field is 15, then the insn is B.
> [...]

One way to model this with CGEN is to act like the operand/opcode
field is opcode only, by replicating instruction A 15 times, each
with a different value (0..14) for the problematic field.  You
might also need some custom operand parsers to assert that each
variant of A will match only if the given logical operand matches
the actual one.

If the only piece of the toolchain producing incorrect behavior is
the disassembler, you may also be able to make it work by turning
off disassembly hashing (#define CGEN_DIS_HASH(buf,value) 0).


- FChE