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understanding-clang-llvm

Repository for understanding and writing LLVM passes.

Building and installing Clang/LLVM

This needs ~40GB disk space and compilation time of ~90min.

  1. Download LLVM-8.0.0, clang-8.0.0

  2. Unzip the LLVM and Clang source files

    tar xf llvm-8.0.0.src.tar.xz
    tar xf cfe-8.0.0.src.tar.xz
    mv cfe-8.0.0.src llvm-8.0.0.src/tools/clang
    
  3. Create your target build folder and make

    mkdir llvm-8.0.0.obj
    cd llvm-8.0.0.obj
    cmake -DCMAKE_BUILD_TYPE=Debug ../llvm-8.0.0.src (or add "-DCMAKE_BUILD_TYPE:STRING=Release" for releae version)
    make -j8  
    
  4. Add paths for LLVM and Clang

    export LLVM_SRC=your_path_to_llvm-8.0.0.src
    export LLVM_OBJ=your_path_to_llvm-8.0.0.obj
    export LLVM_DIR=your_path_to_llvm-8.0.0.obj
    export PATH=$LLVM_DIR/bin:$PATH
    

Converting .c file to bitcode file

The folder examples contains a couple of example .c files which you can play with.

LLVM passes run on bitcode file. Here, we explain how to convert a C file to bitcode file.

clang -c -emit-llvm <path_to_c_file> -o <path_to_output_bitcode_file>

Example:

cd examples
clang -c -emit-llvm simple.c -o simple.bc

LLVM Passes

The folder llvm_passes contains various sample LLVM passes.

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