How to compile subdirectory in lib\Target\XXX

My directory tree as follows:

├── target/
│   └── CMakeLists.txt
│   └── LLVMBuild.txt
│   ├── DSP/
│   │   └── CMakeLists.txt
│   │   └── LLVMBuild.txt
│   │   └── src.cpp
│   │   └── src.h
│   │   ├── subdirectory1
│   │       └── CMakeLists.txt
│   │       └── LLVMBuild.txt
│   │       └──src1.cpp
│   │       └──src1.h

src1.cpp is source file of DSP, like src.cpp.
I think:
1.subdirectory1’s LLVMBuild.txt should be empty(src1.cpp is not a component)
2. subdirectory1’s CMakeList.txt is empty
3. DSP’s CMakeList.txt as follows:
####################################

add_llvm_target(

subdirectory1/src1.cpp

)
add_subdirectory( subdirectory1)
###################################

and it’s compile success in vs2019.
Is it right?

At last, I use llvmbuid.txt just like other subdirectory.