How to get fndecl on C++ CALL_EXPR?

[H.J. Lu]

I am trying to get fndecl on a C++ CALL_EXPR with get_callee_fndecl.
But get_callee_fndecl returns NULL. What is the proper way to
get fndecl on a C++ CALL_EXPR in the middle end?

Thanks.

H.J.