For debugging purposes, it would be useful to have a node in C2 IR that takes a string or integer value that is then printed when the compiled code is executed. For example, this would be useful to print intermediate values in registers / on stack or print errors in verification code.

I think this could be implemented as a CallLeafPureNode to a runtime method that just prints the value (see JDK-8347901).

We already have HaltNodes that print something but then fail hard (which we don't want for this kind of debug printing):

instruct ShouldNotReachHere() %{
  match(Halt);
  format %{ "stop\t# ShouldNotReachHere" %}
  ins_encode %{
    if (is_reachable()) {
      const char* str = __ code_string(_halt_reason);
      __ stop(str);
    }
  %}
  ins_pipe(pipe_slow);
%}

Also, they don't allow printing dynamic values.