I have implemented it, but there is a problem. If I enable the optimization,
EXT_separate_shader_objects must be disabled. Is it okay with you?

This is a valid sequence with EXT_sso:
glUseProgram(prog_with_vs_and_fs);
glUseShaderProgramEXT(prog_with_fs);

prog_with_vs_and_fs cannot be optimized, because the program object can be
bound partially (in this case only the vertex shader from the program object is
bound).

ARB_separate_shader_objects doesn't have this issue.