pass has no effect

[LuoRongLuoRong]

I don't know why. I followed the instructions in the readme. But when finally I use the command clang -flegacy-pass-manager -Xclang -load -Xclang build/skeleton/libSkeletonPass.* something.c and get the a.out and run it, what I get is the same as the result produced by a simple command gcc something.c.

and here is my code structure:

/skeleton/CMakefile.txt:

add_library(SkeletonPass MODULE
    # List your source files here.
    Skeleton.cpp
)

# Use C++11 to compile our pass (i.e., supply -std=c++11).
# target_compile_features(SkeletonPass PRIVATE cxx_range_for cxx_auto_type)

# LLVM is (typically) built with no C++ RTTI. We need to match that;
# otherwise, we'll get linker errors about missing RTTI data.
set_target_properties(SkeletonPass PROPERTIES
    COMPILE_FLAGS "-fno-rtti"
)

# Get proper shared-library behavior (where symbols are not necessarily
# resolved when the shared library is linked) on OS X.
if(APPLE)
    set_target_properties(SkeletonPass PROPERTIES
        LINK_FLAGS "-undefined dynamic_lookup"
    )
endif(APPLE)

/skeleton/Skeleton.cpp

#include "llvm/Pass.h"
#include "llvm/IR/Function.h"
#include "llvm/Support/raw_ostream.h"
#include "llvm/IR/LegacyPassManager.h"
#include "llvm/Transforms/IPO/PassManagerBuilder.h"
using namespace llvm;

namespace {
  struct SkeletonPass : public FunctionPass {
    static char ID;
    SkeletonPass() : FunctionPass(ID) {}

    virtual bool runOnFunction(Function &F) {
      errs() << "I saw a function called " << F.getName() << "!\n";
      return false;
    }
  };
}

char SkeletonPass::ID = 0;

// Automatically enable the pass.
// http://adriansampson.net/blog/clangpass.html
// static void registerSkeletonPass(const PassManagerBuilder &,
//                          legacy::PassManagerBase &PM) {
//   PM.add(new SkeletonPass());
// }
// static RegisterStandardPasses
//   RegisterMyPass(PassManagerBuilder::EP_EarlyAsPossible,
//                  registerSkeletonPass);

// Register the pass so `opt -skeleton` runs it.
static RegisterPass<SkeletonPass> X("skeleton", "a useless pass"); //注册Pass

/CMakeLists.txt

cmake_minimum_required(VERSION 3.1)
project(Skeleton)

# support C++14 features used by LLVM 10.0.0
set(CMAKE_CXX_STANDARD 14)

find_package(LLVM REQUIRED CONFIG)
add_definitions(${LLVM_DEFINITIONS})
include_directories(${LLVM_INCLUDE_DIRS})
link_directories(${LLVM_LIBRARY_DIRS})

add_subdirectory(skeleton)  # Use your pass name here.

/src/demo.cpp

#include <stdio.h>
void func2(){
    printf("hello world");
}

void func(){
    func2();
}

int main(){
    func();
    return 0;
}

Actually, when I run make in /build, I then run opt -load ./libSkeletonPass.so -help | grep skeleton to show information of pass. BUT, I get NOTHING. It means that I don't have any pass.

So, I would like to ask for help. SO MUCH THANKS!

[LuoRongLuoRong]

I found the problem. I didn't follow your instruction completely.
I changed /skeleton/CMakefile.txt. The line target_compile_features(SkeletonPass PRIVATE cxx_range_for cxx_auto_type) should not be omitted.
Then I run commands as follows:

(base) fdse@ubuntu:~/luorong/LLVM/test/llvm-pass-skeleton/build$ cmake ..
-- Configuring done
-- Generating done
-- Build files have been written to: /home/fdse/luorong/LLVM/test/llvm-pass-skeleton/build

(base) fdse@ubuntu:~/luorong/LLVM/test/llvm-pass-skeleton/build$ make
Consolidate compiler generated dependencies of target SkeletonPass
[ 50%] Building CXX object skeleton/CMakeFiles/SkeletonPass.dir/Skeleton.cpp.o
[100%] Linking CXX shared module libSkeletonPass.so
[100%] Built target SkeletonPass

(base) fdse@ubuntu:~/luorong/LLVM/test/llvm-pass-skeleton/build$ cd skeleton/

(base) fdse@ubuntu:~/luorong/LLVM/test/llvm-pass-skeleton/build/skeleton$ ls
CMakeFiles  cmake_install.cmake  libSkeletonPass.so  Makefile
(base) fdse@ubuntu:~/luorong/LLVM/test/llvm-pass-skeleton/build/skeleton$ opt -load ./libSkeletonPass.so -help | grep skeleton
      --skeleton                                                           - a useless pass

(base) fdse@ubuntu:~/luorong/LLVM/test/llvm-pass-skeleton/build/skeleton$ cd ../../src

(base) fdse@ubuntu:~/luorong/LLVM/test/llvm-pass-skeleton/src$ clang++ -O0 -g -S -emit-llvm demo.cpp -o demo.ll

(base) fdse@ubuntu:~/luorong/LLVM/test/llvm-pass-skeleton/src$ ls
demo.cpp  demo.ll

(base) fdse@ubuntu:~/luorong/LLVM/test/llvm-pass-skeleton/src$ opt -load ../build/skeleton/libSkeletonPass.so -skeleton demo.ll -enable-new-pm=0
WARNING: You're attempting to print out a bitcode file.
This is inadvisable as it may cause display problems. If
you REALLY want to taste LLVM bitcode first-hand, you
can force output with the `-f' option.

I saw a function called _Z5func2v!
I saw a function called _Z4funcv!
I saw a function called main!