How to define and read CLI arguments for an LLVM Pass with the new Pass Manager?

Question

I'm wondering if there is a way to define, and read the value of, CLI arguments in an LLVM pass plugin? I'm basing my plugin off of banach-space/llvm-tutor, specifically InjectFuncCall. Let's say I want to pass in an argument -func=foo to say only inject into functions called foo. How exactly do I define this command-line argument?

I tried using the CommandLine 2.0 Library. And saw this Answer, but I can't get opt to recognize my argument.

Yes, I am. The final product is a `.so` that I tell `opt` to load. Is that an issue? — Axel Munoz, Apr 22 '21 at 12:03
When you get it to work, tell me how ;) It should work, I couldn't coerce it to actually work, after some swearing I'm using `.a` for now. — arnt, Apr 22 '21 at 12:14
Will do :) Do you have resources/documentation on building and using `.a` files for `opt` passes? — Axel Munoz, Apr 22 '21 at 12:48
In-tree? It's simple, just add them to cmakefiles and you're done. Haven't tried out of tree. — arnt, Apr 22 '21 at 13:02

score 6 · Answer 1 · answered Apr 05 '22 at 11:58

I have found out that you can use the arguments with the new pass manager if you use opt -load yourLib.so. In this case the command will look like this:

opt -load ./build/libHelloWorld.so -load-pass-plugin=./build/libHelloWorld.so \ 
-passes="hello-world" -disable-output -lists MYARG1 -lists MYARG2 ./input_for_hello.ll

Below is the full reproducible example.

HelloWorld.cpp:

#include "llvm/IR/LegacyPassManager.h"
#include "llvm/Passes/PassBuilder.h"
#include "llvm/Passes/PassPlugin.h"
#include "llvm/Support/raw_ostream.h"
#include "llvm/Support/CommandLine.h"

using namespace llvm;

namespace {

// Here we register the pass arguments
cl::list<std::string> Lists("lists", cl::desc("Specify names"), cl::OneOrMore);

// This method implements what the pass does
void visitor(Function &F) {
    // using the pass arguments
      for(auto arg: Lists) {
        errs() << "arg: " << arg << "\n";
      }
    errs() << "(llvm-tutor) Hello from: "<< F.getName() << "\n";
    errs() << "(llvm-tutor)   number of arguments: " << F.arg_size() << "\n";
}

// New PM implementation
struct HelloWorld : PassInfoMixin<HelloWorld> {
  // Main entry point, takes IR unit to run the pass on (&F) and the
  // corresponding pass manager (to be queried if need be)
  PreservedAnalyses run(Function &F, FunctionAnalysisManager &) {
    visitor(F);
    return PreservedAnalyses::all();
  }
};

} // namespace

//-----------------------------------------------------------------------------
// New PM Registration
//-----------------------------------------------------------------------------
llvm::PassPluginLibraryInfo getHelloWorldPluginInfo() {
  return {LLVM_PLUGIN_API_VERSION, "HelloWorld", LLVM_VERSION_STRING,
          [](PassBuilder &PB) {
            PB.registerPipelineParsingCallback(
                [](StringRef Name, FunctionPassManager &FPM,
                   ArrayRef<PassBuilder::PipelineElement>) {
                  if (Name == "hello-world") {
                    FPM.addPass(HelloWorld());
                    return true;
                  }
                  return false;
                });
          }};
}

// This is the core interface for pass plugins. It guarantees that 'opt' will
// be able to recognize HelloWorld when added to the pass pipeline on the
// command line, i.e. via '-passes=hello-world'
extern "C" LLVM_ATTRIBUTE_WEAK ::llvm::PassPluginLibraryInfo
llvmGetPassPluginInfo() {
  return getHelloWorldPluginInfo();
}

CMakeLists.txt:

cmake_minimum_required(VERSION 3.13.4)
project(llvm-tutor-hello-world)

#===============================================================================
# 1. LOAD LLVM CONFIGURATION
#===============================================================================
# Set this to a valid LLVM installation dir
set(LT_LLVM_INSTALL_DIR "" CACHE PATH "LLVM installation directory")

# Add the location of LLVMConfig.cmake to CMake search paths (so that
# find_package can locate it)
list(APPEND CMAKE_PREFIX_PATH "${LT_LLVM_INSTALL_DIR}/lib/cmake/llvm/")

# FIXME: This is a warkaround for #25. Remove once resolved and use
# find_package(LLVM 11.0.0 REQUIRED CONFIG) instead.
find_package(LLVM REQUIRED CONFIG)

# HelloWorld includes headers from LLVM - update the include paths accordingly
include_directories(SYSTEM ${LLVM_INCLUDE_DIRS})

#===============================================================================
# 2. LLVM-TUTOR BUILD CONFIGURATION
#===============================================================================
# Use the same C++ standard as LLVM does
set(CMAKE_CXX_STANDARD 14 CACHE STRING "")

# LLVM is normally built without RTTI. Be consistent with that.
if(NOT LLVM_ENABLE_RTTI)
  set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -fno-rtti")
endif()

#===============================================================================
# 3. ADD THE TARGET
#===============================================================================
add_library(HelloWorld SHARED HelloWorld.cpp)

# Allow undefined symbols in shared objects on Darwin (this is the default
# behaviour on Linux)
target_link_libraries(HelloWorld
  "$<$<PLATFORM_ID:Darwin>:-undefined dynamic_lookup>")

input_for_hello.ll:

; ModuleID = '../inputs/input_for_hello.c'
source_filename = "../inputs/input_for_hello.c"
target datalayout = "e-m:e-p270:32:32-p271:32:32-p272:64:64-i64:64-f80:128-n8:16:32:64-S128"
target triple = "x86_64-pc-linux-gnu"

; Function Attrs: mustprogress nofree norecurse nosync nounwind readnone uwtable willreturn
define dso_local i32 @foo(i32 %0) local_unnamed_addr #0 {
  %2 = shl nsw i32 %0, 1
  ret i32 %2
}

; Function Attrs: mustprogress nofree norecurse nosync nounwind readnone uwtable willreturn
define dso_local i32 @bar(i32 %0, i32 %1) local_unnamed_addr #0 {
  %3 = shl i32 %1, 2
  %4 = add nsw i32 %3, %0
  ret i32 %4
}

; Function Attrs: mustprogress nofree norecurse nosync nounwind readnone uwtable willreturn
define dso_local i32 @fez(i32 %0, i32 %1, i32 %2) local_unnamed_addr #0 {
  %4 = shl i32 %1, 2
  %5 = add nsw i32 %4, %0
  %6 = shl nsw i32 %5, 1
  %7 = mul nsw i32 %2, 3
  %8 = add i32 %7, %0
  %9 = add i32 %8, %6
  ret i32 %9
}

; Function Attrs: mustprogress nofree norecurse nosync nounwind readnone uwtable willreturn
define dso_local i32 @main(i32 %0, i8** nocapture readnone %1) local_unnamed_addr #0 {
  ret i32 12915
}

attributes #0 = { mustprogress nofree norecurse nosync nounwind readnone uwtable willreturn "frame-pointer"="none" "min-legal-vector-width"="0" "no-trapping-math"="true" "stack-protector-buffer-size"="8" "target-cpu"="x86-64" "target-features"="+cx8,+fxsr,+mmx,+sse,+sse2,+x87" "tune-cpu"="generic" }

!llvm.module.flags = !{!0, !1}
!llvm.ident = !{!2}

!0 = !{i32 1, !"wchar_size", i32 4}
!1 = !{i32 7, !"uwtable", i32 1}
!2 = !{!"Ubuntu clang version 13.0.1-++20220120110924+75e33f71c2da-1~exp1~20220120231001.58"}

Build steps:

rm -rf ./build
mkdir "build"
cd build || exit
cmake ..
cmake --build .

Run the pass:

opt -load ./build/libHelloWorld.so -load-pass-plugin=./build/libHelloWorld.so \ 
-passes="hello-world" -disable-output -lists MYARG1 -lists MYARG2 ./input_for_hello.ll

Output:

arg: MYARG1
arg: MYARG2
(llvm-tutor) Hello from: foo
(llvm-tutor)   number of arguments: 1
arg: MYARG1
arg: MYARG2
(llvm-tutor) Hello from: bar
(llvm-tutor)   number of arguments: 2
arg: MYARG1
arg: MYARG2
(llvm-tutor) Hello from: fez
(llvm-tutor)   number of arguments: 3
arg: MYARG1
arg: MYARG2
(llvm-tutor) Hello from: main
(llvm-tutor)   number of arguments: 2

I can confim that loading using the old -load syntax alongside the new -load-pass-plugin allows me to use my custom command line arguments again. Is there any timeline for getting this functionality working again within the new pass manager? — andylshort, May 31 '22 at 12:12

How to define and read CLI arguments for an LLVM Pass with the new Pass Manager?

1 Answers1