System Tasks and Functions in Yosys

[Muxianesty]

Greetings everyone.
I've been introduced to Yosys only a bit ago and still do not understand many things about it.
I wanted to ask whether there is some kind of principle on which Verilog builtin (system) tasks support is added to Yosys.

Currently in frontends/ast/simplify.cc inside the function with same name as the file some tasks like $display, $monitor, $readmemh are recognized.

I wanted to test some benchmarks from the Verilog 1364-2005 standard itself, namely sections 17.2.6 Flushing output and 17.2.7 I/O error status with Yosys using some straightforward tests:

module test;

  integer fd, mcd;

  initial begin
    $fflush(mcd);
    $fflush(fd);
    $fflush();
  end
endmodule

module test;

  integer fd, errno;
  reg str;

  initial begin
    errno = $ferror(fd, str);
  end
endmodule

And both tests fail:

ERROR: Can't resolve task name `\$fflush'.
ERROR: Can't resolve function name `\$ferror'.

I thought tasks such as these can be ignored the way it is with some calls (frontends/ast/simplify.cc:1050):

if ((type == AST_FCALL || type == AST_TCALL) && (str == "$strobe" || str == "$monitor" || str == "$time" ||
			str == "$dumpfile" || str == "$dumpvars" || str == "$dumpon" || str == "$dumpoff" || str == "$dumpall")) {
		log_file_warning(filename, location.first_line, "Ignoring call to system %s %s.\n", type == AST_FCALL ? "function" : "task", str.c_str());

Is there an explicit purpose for these tasks to not be recognized or they were simply forgotten?

Thank you all in advance.

[whitequark]

Yosys generally implements only the tasks that are useful during synthesis, and tasks like $dumpvars are not. Since it is benign to ignore them (they don't affect synthesis results) they are ignored.

This is done purely on a case by case basis.

[Muxianesty]

So it actually makes some sense to make a feature-type issue on Yosys Github to request more system tasks be added to "ignore list".

Yes, they do not affect synthesis and not many people will ever need them, but for some sort of "completeness" they might be acknowledged as well.

Thank you very much for your answer.