[Iverilog-devel] bit/part-select of function return value

[Evan L. <sa2...@cy...>]

Icarus and VCS don't allow this, but Xcelium, Questa, and Riviera-PRO do.

The LRM does appear to agree with Icarus - the BNF only allows selects
of identifiers, and the explanatory text seems to agree ("Bit-selects
and part-selects of vector regs, integer variables, and time variables
shall be allowed").

However, this is really pretty dumb: either a function returns an rvalue
that can be used in an expression, or it doesn't, in which case it's
something special and unusual. A function can return "Bit-selects and
part-selects of vector regs, etc", which indicates (to me, anyway) that
you should be able to apply a select to it.

Might be worth going with Xcelium on this one?? OTOH, all the simulators
agree that you can't apply a select to a primary in general (8'ha5[3:0]
is illegal for all sims, for example), so maybe this is a step too far.

Test code at https://www.edaplayground.com/x/9jLz, and below:

module test;
  reg [7:0] a;
  reg [3:0] b;

  initial begin
    a = 8'ha5;
    b = f1(0)[3:0];
    $display("a is %b; b is %b", a, b);
  end

  function [7:0] f1(input dummy);
    f1 = a;
  endfunction
endmodule