Found this while working on jcstress support, see CODETOOLS-7902865. jcstress opts in to PrintAssembly for the particular method by using the compile directive:
 https://github.com/openjdk/jcstress/blob/master/jcstress-core/src/main/java/org/openjdk/jcstress/TestExecutor.java#L246-L248

When supplied on JVM command line, -XX:+PrintAssembly implicitly enables -XX:+DebugNonSafepoints:

jint Arguments::apply_ergo() {
  ...
  if (PrintAssembly && FLAG_IS_DEFAULT(DebugNonSafepoints)) {
    warning("PrintAssembly is enabled; turning on DebugNonSafepoints to gain additional output");
    DebugNonSafepoints = true;
  }
  ...
}

When -XX:CompileCommand=Print is used, it also opts in:

void compilerOracle_init() {
  ...
  if (has_command(CompileCommand::Print)) {
    if (PrintAssembly) {
      warning("CompileCommand and/or %s file contains 'print' commands, but PrintAssembly is also enabled", default_cc_file);
    } else if (FLAG_IS_DEFAULT(DebugNonSafepoints)) {
      warning("printing of assembly code is enabled; turning on DebugNonSafepoints to gain additional output");
      DebugNonSafepoints = true;
    }
  }
  ...

But CompilerDirectives do not seem to have the same heuristics.