lldb failed to step into functions of shared library

Hi all:
I'm having trouble with lldb3.8 on ubuntu16.04.
lldb failed to step in functions of my shared library while gdb can.
The code is very simple:

main.cpp:

    int main(int argc, char *argv[])
    {
        MyLib ml;
        ml.foo0();
        ml.foo1();
        return 0;
    }

MyLib.h:

    class MyLib {
    public:
      void foo0() {
        int i = 5;
        std::cout << i;
      }
      void foo1();
    };

MyLib.cpp:

    void MyLib::foo1() {
      int i = 5;
      std::cout << i;
    }

lldb can step in foo0, but failed to step in foo1. Gdb can step into foo1, so i think debug symbol is successfully created. If i set a break point at definition of foo1, lldb will stop at the breakpoint. I have no clew why would this happen, don't know if it's a bug or not. Pls help me if you know how to make it work!