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

How to create own Transforms pass directory in llvm-3.4

Step 1: Go to the llvm Transforms directory and create directory MyLLVMPasses 

            (you can give any directory name)

cd llvm/lib/Transforms mkdir MyLLVMPasses

Step 2: Add directory name MyLLVMPasses in Transforms/CmakeLists.txt file 

add_subdirectory(MyLLVMPasses)

Step 3: Add directory name MyLLVMPasses in Transforms/LLVMBuild.txt file

[common] subdirectories = IPO InstCombine Instrumentation Scalar Utils Vectorize ObjCARC MyLLVMPasses

Step 4: Add directory name MyLLVMPasses in Transforms/Makefile file

PARALLEL_DIRS = Utils Instrumentation Scalar InstCombine IPO Vectorize Hello ObjCARC MyLLVMPasses

Step 5: Create CmakeLists.txt file in  MyLLVMPasses directory and write these lines

add_llvm_library(LLVMMyLLVMPasses   ) add_dependencies(LLVMMyLLVMPasses intrinsics_gen)

Step 6: Create LLVMBuild.txt file in MyLLVMPasses directory and write these lines

[component_0] type = Library name = MyLLVMPasses parent = Transforms library_name = MyLLVMPasses required_libraries = Analysis Core Support Target TransformUtils

Step 7:  Create Makefile in MyLLVMPasses directory and write these lines

LEVEL = ../../.. LIBRARYNAME = LLVMMyLLVMPasses BUILD_ARCHIVE = 1 include $(LEVEL)/Makefile.common

Step 8: Create MyLLVMPasses.cpp file in MyLLVMPasses directory and write these lines

#include "llvm/Transforms/MyLLVMPasses.h" #include "llvm-c/Initialization.h" #include "llvm-c/Transforms/MyLLVMPasses.h" #include "llvm/Analysis/Passes.h" #include "llvm/IR/Verifier.h" #include "llvm/InitializePasses.h" #include "llvm/PassManager.h" using namespace llvm; // initializeMyLLVMPasses - Initialize all passes linked into the // MyLLVMPasses library. void llvm::initializeMyLLVMPasses(PassRegistry &Registry) {   // nothing is needed here yet } void LLVMInitializeMyLLVMPasses(LLVMPassRegistryRef R) {   initializeMyLLVMPasses(*unwrap(R)); }

Step 9: Create MyLLVMPasses.h file in llvm/include/llvm/Transforms and write these lines

#ifndef LLVM_TRANSFORMS_MYLLVMPASSES_H #define LLVM_TRANSFORMS_MYLLVMPASSES_H #include "llvm/ADT/StringRef.h" namespace llvm { class FunctionPass; class Pass; } // End llvm namespace #endif

Step 10: Create MyLLVMPasses.h file in llvm/include/llvm-c/Transforms and write these lines

#ifndef LLVM_C_TRANSFORMS_MYLLVMPASSES_H #define LLVM_C_TRANSFORMS_MYLLVMPASSES_H #include "llvm-c/Core.h" #ifdef __cplusplus extern "C" { #endif // LLVMCTransformsMyLLVMPasses MyLLVMPasses transformations #ifdef __cplusplus } #endif /* defined(__cplusplus) */ #endif

Step 11: Open llvm/include/llvm-c/Initialization.h file, add this line

void LLVMInitializeMyLLVMPasses(LLVMPassRegistryRef R);

Step 12: Open llvm/include/llvm/InitializePasses.h file, add this line

// initializeMyLLVMPasses - Initialize all passes linked into the // MyLLVMPasses library. void initializeMyLLVMPasses(PassRegistry&);

Step 13: Add directory name MyLLVMPasses in lib/Transforms/IPO/LLVMBuild.txt file

[component_0] type = Library name = IPO parent = Transforms library_name = ipo required_libraries = Analysis Core IPA InstCombine Scalar Support Target TransformUtils Vectorize MyLLVMPasses

Step 14: Include MyLLVMPasses.h file in llvm/include/llvm/LinkAllPasses.h file

#include "llvm/Transforms/MyLLVMPasses.h"

Step 15: Include MyLLVMPasses.h file in llvm/tools/clang/lib/CodeGen/BackendUtil.cpp file

#include "llvm/Transforms/MyLLVMPasses.h"

see How to create LLVM Transforms pass

get bitcode(.bc) from source in llvm/clang

get bytecode from C++ program. 

test.cpp

int main() {   const int count = 3;   const int value = 5;   int result = count + value;   return 0; }

get bytecode.

clang++ -c -emit-llvm test.cpp -o testbyte.bc -S

read bytecode file (testbyte.bc).

vim testbyte.bc

testbyte.bc

. . . ; Function Attrs: nounwind uwtable define i32 @main() #0 { entry:   %retval = alloca i32, align 4   %count = alloca i32, align 4   %value = alloca i32, align 4   %result = alloca i32, align 4   store i32 0, i32* %retval   store i32 3, i32* %count, align 4   store i32 5, i32* %value, align 4   store i32 8, i32* %result, align 4   ret i32 0 } . . .

Install LLVM/Clang in Linux/Ubuntu using git

Step 1: 
Download LLVM and Clang

git clone http://llvm.org/git/llvm.git llvm cd llvm/tools git clone http://llvm.org/git/clang.git clang

Step 2: 
Configure and install LLVM and Clang

cd ../ mkdir build  (for building without polluting the source directory) cd build ../configure --enable-optimized --enable-assertions                                 --prefix=/home/user/llvm/install make make install

for more information about configure and install see. Getting Started with the LLVM System

Step 3: 
Testing LLVM/Clang, compile small C++ program (test.cpp)

// test.cpp #include <iostream> using namespace std; int main(int argc, char *argv[]) {   cout << "Hello LLVM/Clang" << "\n";   return 0; }

Step 4: 
Run

/home/user/llvm/install/bin/clang++ test.cpp -o hello ./hello

Output:

Hello LLVM/Clang