How to create LLVM transforms pass with Clang option (flag) in llvm-3.4

We are going to create Module Pass. In the same way it is possible to create Function, BasicBlock, etc. Instead of Module use Function, BasiBlock, etc

Step 1: Got to the llvm/lib/Transformas/MyLLVMPasses directory.

(see how to create own directory like MyLLVMPasses) 

cd llvm/lib/Transformas/MyLLVMPasses

Step 2: Create NewLlvmPass.cpp file (you can give any name) in MyLLVMPasses  directory and write there this code

#include "llvm/Transforms/MyLLVMPasses.h" #include "llvm/Support/raw_ostream.h" #include "llvm/Transforms/Scalar.h" #include "llvm/Pass.h" using namespace llvm; namespace { class NewLlvmPass : public ModulePass { public:     static char ID;     NewLlvmPass() : ModulePass(ID) {       initializeNewLlvmPassPass(*PassRegistry::getPassRegistry());     }     bool runOnModule(Module &M);  }; } // end namespace char NewLlvmPass::ID = 0; INITIALIZE_PASS_BEGIN(NewLlvmPass, "myoption", "New LLVM Pass", false, false) INITIALIZE_PASS_END(NewLlvmPass, "myoption", "New LLVM Pass", false, false) ModulePass *llvm::createNewLlvmPassPass() {   return new NewLlvmPass(); } // runOnModule(Module &M) is like main() bool NewLlvmPass::runOnModule(Module &M) {   bool Changed = false;   errs() << "New LLVM Pass" << "\n";   return Changed; }

Step 3: Open llvm/include/llvm/Transforms/MyLLVMPasses.h file. After class decelerations add this code

ModulePass *createNewLlvmPassPass();

Step 4: Open llvm/include/llvm/LinkAllPasses.h file. Add this code.

(void) llvm::createNewLlvmPassPass();

Step 5: Open llvm/include/llvm/InitializePasses.h file and in end of file add this code

void initializeNewLlvmPassPass(PassRegistry&);

Step 6: Open llvm/include/llvm-c/Transforms/MyLLVMPasses.h file and add this line

void LLVMAddNewLlvmPassPass(LLVMPassManagerRef PM);

see below

extern "C" { #endif /** See llvm::createNewLlvmPassPass function. */ void LLVMAddNewLlvmPassPass(LLVMPassManagerRef PM); #ifdef __cplusplus }

Step 7: Open llvm/lib/Transforms/MyLLVMPasses/CmakeLists.txt file. Add in file pass' file name.

add_llvm_library(LLVMMyLLVMPasses   NewLlvmPass.cpp   ) add_dependencies(LLVMMyLLVMPasses intrinsics_gen)

Step 8: Open llvm/lib/Transforms/MyLLVMPasses/MyLLVMPasses.cpp file. Add lines which are highlighted.

// initializeMyLLVMPasses - Initialize all passes linked into the // MyLLVMPasses library. void llvm::initializeMyLLVMPasses(PassRegistry &Registry) {   initializeNewLlvmPassPass(Registry); } void LLVMInitializeMyLLVMPasses(LLVMPassRegistryRef R) {   initializeMyLLVMPasses(*unwrap(R)); } void LLVMAddNewLlvmPassPass(LLVMPassManagerRef PM) {   unwrap(PM)->add(createNewLlvmPassPass()); }

Step 9: Open file llvm/tools/clang/lib/Frontend/CompilerInvocation.cpp file. Add line

Opts.NewLlvmPass = Args.hasArg(OPT_enable_myoption);

in function ParseCodeGenArgs, after those lines (see below).

Opts.VectorizeBB = Args.hasArg(OPT_vectorize_slp_aggressive); Opts.VectorizeLoop = Args.hasArg(OPT_vectorize_loops); Opts.VectorizeSLP = Args.hasArg(OPT_vectorize_slp); Opts.NewLlvmPass = Args.hasArg(OPT_enable_myoption);

Step 10: Open llvm/tools/clang/lib/CodeGen/BackendUtil.cpp file. In end of 

EmitAssemblyHelper::CreatePasses() functio add this code

if (CodeGenOpts.NewLlvmPass) {   MPM->add(createNewLlvmPassPass()); }

Step 11: Open llvm/tools/clang/include/clang/Frontend/CodeGenOptions.def file. Add this line

CODEGENOPT(NewLlvmPass       , 1, 0)  ///< Run My New LLVM pass

you can add it after Vectorize, like this

CODEGENOPT(VectorizeSLP , 1, 0)  /// < Run SLP vectorizer. CODEGENOPT(NewLlvmPass  , 1, 0)  /// < Run My New LLVM pass

Now we must add our Clang option, which we named "-myoption"

Step 12: Open llvm/tools/clang/lib/Driver/Tools.cpp file and in Clang::ConstructJob function add this code

if (Args.hasArg(options::OPT_enable_myoption))   CmdArgs.push_back("-myoption");

Step 13: Open llvm/tools/clang/include/clang/Driver/Options.td file. Add these lines

def enable_myoption : Flag<["-"], "myoption">, Flags<[CC1Option]>,   HelpText<"New LLVM Pass">;

you can add it before  // standard options comment.

Step 14: Now go to check LLVM pass with Clang option.

make make install

Step 15: Run (path_to_install_dir is absolute path where installed clang/clang++ )

path_to_install_dir/clang++ -mayoption test.cpp

Output during compilation.

New LLVM Pass