Re: Simulator: base_insn and insn in decode.c

[Dave Brolley <brolley@redhat.com>]

I forgot to address your other question which was about the difficulty 
of setting entire_insn before decoding. It's a bit of a chicken and egg 
situation isnt'y it? You can't set entire insn properly until you know 
something about the insn, but you can't call decode without setting 
entire_insn properly.

Your method of calling decode twice won't work because of this.

Most existing ports determine the insn length by looking at a few bits 
in base_insn and use this information to fill entire_insn.

I'm wondering if the decoder shouldn't be redesigned so that all it 
takes is base_insn, which should be all that is necessary to identify 
the insn. The extractors for each format would then read any additional 
bytes as needed. There is already support for this for ISAs with insns 
which are longer than an insn word.

Dave