Building simple c++ MLIR program with local LLVM build

Beginners
1

Hi! I’m trying to build a simple MLIR program using C++ API using locally build LLVM.

I build my LLVM instance with:

cmake -G Ninja ../llvm -DLLVM_ENABLE_PROJECTS="mlir;llvm;clang;lld" -DLLVM_TARGETS_TO_BUILD="Native" -DCMAKE_BUILD_TYPE=Release -DMLIR_ENABLE_BINDINGS_PYTHON=ON -DPython3_EXECUTABLE="..." -DLLVM_INSTALL_UTILS=ON -DMLIR_INCLUDE_INTEGRATION_TESTS=ON -DLLVM_BUILD_EXAMPLES=ON

And installed with:

cmake -DCMAKE_INSTALL_PREFIX=../build-install -P cmake_install.cmake

Here’s a example.ccp file that I have:

#include "mlir/IR/MLIRContext.h"

int main() {
  mlir::MLIRContext context;
  return 0;
}

And here’s CMakeLists.txt file:

cmake_minimum_required(VERSION 3.30)
project(MLIR_example)
set(CMAKE_CXX_STANDARD 17)

include_directories(${LLVM_PROJECT_DIR}/build-install/include)
link_directories(${LLVM_PROJECT_DIR}/build-install/lib)

add_executable(example example.cpp)
target_link_libraries(example PUBLIC mlir_c_runner_utils LLVMSupport)

But running cmake -G Ninja ../ and ninja results in error:

[1/1] Linking CXX executable example
FAILED: example
: && /usr/bin/c++   CMakeFiles/example.dir/example.cpp.o -o example -L/home/mtsokol/llvm-project-main/build/lib -Wl,-rpath,/home/mtsokol/llvm-project-main/build/lib  -lmlir_c_runner_utils  -lLLVMSupport && :
/usr/bin/ld: CMakeFiles/example.dir/example.cpp.o: in function `main':
example.cpp:(.text+0x29): undefined reference to `mlir::MLIRContext::MLIRContext(mlir::MLIRContext::Threading)'
/usr/bin/ld: example.cpp:(.text+0x3a): undefined reference to `mlir::MLIRContext::~MLIRContext()'
collect2: error: ld returned 1 exit status
ninja: build stopped: subcommand failed.

Thank you for any beginners tips on what I have missed in my setup!

2 
target_link_libraries(example PUBLIC mlir_c_runner_utils LLVMSupport)

I don’t know how you selected this list?
In general you need to look at the header you include in your .cpp file, and include the corresponding libraries.
Here you have a single one: #include "mlir/IR/MLIRContext.h"

So the library providing the implementation for this header is MLIRIR.

If you have a doubt, you can check in the mlir/lib/IR/CMakeLists.txt file the name of the library.

3

@mehdi_amini Thank you for help!

MLIRIR was required indeed - I managed to get my example up and running. Here’s a list of link libraries that I needed:

target_link_libraries(
    example
    MLIRIR
    LLVMSupport
    LLVMDemangle
    MLIRSupport
)

What surprised me was the fact that the order of elements in the list matters.

4

I’m surprised you needed more than MLIRIR, CMake is supposed to handle the transitive dependencies itself.

5

@mehdi_amini Hmm, then I think something might be broken with transitive dependencies.

If anyone is interested in the future here’s a small repository that reproduces this issue: GitHub - mtsokol/example-mlir-cpp

Here’s a folder with working example: example-mlir-cpp/case_running at main · mtsokol/example-mlir-cpp · GitHub
And passing CI job: Initial commit · mtsokol/example-mlir-cpp@0506c10 · GitHub
with CMakeLists libs:

target_link_libraries(
    example
    MLIRIR
    LLVMSupport
    LLVMDemangle
    MLIRSupport
    )

Here’s a folder with failing example: example-mlir-cpp/case_failing at main · mtsokol/example-mlir-cpp · GitHub
And failing CI job: Initial commit · mtsokol/example-mlir-cpp@0506c10 · GitHub
with CMakeLists libs:

target_link_libraries(
    example
    MLIRIR
    )
6

Looks that the other option is to build LLVM with:

-DLLVM_BUILD_LLVM_DYLIB=ON

And then there’s a libLLVM.so and libMLIR.so and it’s sufficient to link just them.

7

It may be worth taking at look at the standalone example:
https://github.com/llvm/llvm-project/tree/main/mlir/examples/standalone

There’s been a related talk at FOSDEM 2023, “How to Build your own MLIR Dialect”, which also goes through setting up CMakeLists.txt: