Re: [Iverilog-devel] Wondering aloud about extended operand lists

[Cary R. <cy...@ya...>]

--- Stephen Williams <st...@ic...> wrote:

> There are a handful of instructions in the vvp opcodes set that
> are really pressed for operands. They are reduced to using implicit
> index variables to carry operands that really can generally be
> immediate.
> 
> So I'm wondering aloud if maybe it *is* time to extend the size
> of the opcode space. In particular, I've been thinking of
> adding to the second union a pointer to a vvp_code_extend_s
> struct. This struct can be *much* more liberal, and can carry
> more number values. This may wind up allowing us to replace
> several hackish instructions with instructions with longer
> operand lists.

Should this be done with the second argument or should it be collapsed
down to a single argument. Something like:

struct vvp_code_s {
  vvp_code_fun opcode; /* This determines the number/type of arguments. */

  union {
    some_inclusive_arg_type_union single_arg;
    some_inclusive_arg_type_union *array_of_args;
  }
}

There is probably a trade off somewhere based on the argument distribution
which may change as the opcodes are reviewed. Having a larger/arbitrary
number of arguments would allow us to build more complex opcodes that
should help performance (both speed and memory).

Cary


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