ciEnv::_break_at_compile is set in compilerBroker but never be referred.
c1 and c2 check _directive->BreakAtCompileOption individually. 

it actually voids the following condtion.
  should_break = directive->BreakAtExecuteOption || task->check_break_at_flags();

first of all,  it sounds like it should be BreakAtCompileOption. 
second, the following flags are all ignored.

// CompileTask::check_break_at_flags
bool CompileTask::check_break_at_flags() {
  int compile_id = this->_compile_id;
  bool is_osr = (_osr_bci != CompileBroker::standard_entry_bci);

  if (CICountOSR && is_osr && (compile_id == CIBreakAtOSR)) {
    return true;
  } else {
    return (compile_id == CIBreakAt);
  }
}