Final blocks and non-blocking assignments?

[jrudess]

To learn the code-base, I picked (at random) a failing ivtest case to try and resolve: https://chipsalliance.github.io/sv-tests-results/#Slang|ivtest|regress-sv_program3b_iv

To avoid Program related issues, (since no one cares about Programs :-), I changed the test case to be simpler:

module main;
    int unsigned test;
    final begin
        test = 3;
        test <= 5;
        if (test == 5) begin
            $display("FAILURE -- non-blocking assignment in final should not update LHS");
        end else begin
            $display("PASSED");
        end
    end
endmodule

The ivtest appears to want non-blocking assignments in final-blocks to be rejected at compile. The LRM says:

9.2.3 Final Procedures

The only statements allowed inside a final procedure are those permitted inside a function declaration, so that they execute within a single simulation cycle. Unlike an initial procedure, the final procedure does not execute as a separate process; instead, it executes in zero time, as a series of function calls from a single process. All final procedures shall execute in an arbitrary order. No remaining scheduled events shall execute after all final procedures have executed.

VCS accepts this code which seems LRM compliant and the ivtest appears wrong. On the other hand, a non-blocking assignment in a final-block is nonsensical since it becomes a no-op and this is almost certainly a coding error if it occurs, so flagging an error does seem appropriate. Any opinions?

Note: To implement the check, I ended up splitting out FunctionOrFinal to be independent Function/Final flags, but there may have been a simpler method.

[MikePopoloski]

Hmm yeah, I think a strict reading implies this is legal, but as you say it's a useless statement. VCS allows this, Questa disallows it, and Xcelium reports a warning. I think that latter approach is best; issue an on-by-default warning that the statement is likely a mistake.

I agree that this probably means we need a separate BindFlag for Function and Final.