关于llvm:基于legacy-pass-manager的pass编写

1. 在 github 页面下载最新的 llvm 工程, 当初最新的版本应该对应着是 llvm13

2. 在 llvm-project/llvm/lib/Transforms 文件夹新建自定义的 pass 文件夹

cd llvm-project/llvm/lib/Transforms

mkdir MyPass

在 MyPass 文件夹下新建一个 CMakeLists.txt

写入

add_llvm_library( MYPass MODULE
  MYPass.cpp

  DEPENDS
  intrinsics_gen
  PLUGIN_TOOL
  opt
  )

3. 在 llvm-project/llvm/lib/Transforms/CmakeLists.txt 中增加文件夹目录

add_subdirectory(MYPass)

4. 编写 Pass

#include "llvm/ADT/Statistic.h"
#include "llvm/IR/Function.h"
#include "llvm/Pass.h"
#include "llvm/Support/raw_ostream.h"
#include "llvm/IR/LegacyPassManager.h"
#include "llvm/Transforms/IPO/PassManagerBuilder.h"

using namespace llvm;

#define DEBUG_TYPE "hello"

STATISTIC(HelloCounter, "Counts number of functions greeted");

namespace {
  // Hello - The first implementation, without getAnalysisUsage.
struct Hello : public FunctionPass {
    static char ID; // Pass identification, replacement for typeid
    Hello() : FunctionPass(ID) {}
    
    bool runOnFunction(Function &F) override {
        ++HelloCounter;
        errs() << "Hello:";
        errs().write_escaped(F.getName()) << '\n';
        return false;
    }
    void getAnalysisUsage(AnalysisUsage &AU) const override {AU.setPreservesAll();
    }
    
    void releaseMemory() override {errs() << "releaseMemory";
    }

};
}

char Hello::ID = 0;
static RegisterPass<Hello> X("hello", "Hello World Pass",false,false);

static RegisterStandardPasses Y2(PassManagerBuilder::EP_EarlyAsPossible,[](const PassManagerBuilder &Builder,legacy::PassManagerBase &PM) {PM.add(new Hello());
     
});

5. 构建和编译 pass

cd /yourPath/llvm-project

cmake -S llvm -B build -G Xcode -DLLVM_ENABLE_PROJECTS="clang;libcxx;libcxxabi"

在 xcode 里抉择 sechme:MYPass, 开始编译
编译实现后，可在 llvm-project/build/Debug/bin 目录下找到编译后的可执行文件, 以及 llvm-project/build/Debug/lib 目录下找到 LLVM pass 的动静库
5.opt 应用 MYPass.dylib, 这里官网文档有误, 须要通过 -enable-new-pm= 0 指定用 legacy pass manager

./opt -load ../lib/LLVMHello.dylib -hello -enable-new-pm=0 < hello.bc >/dev/null

6.clang 应用 MYPass.dylib, 这里官网文档有误, 须要通过 -flegacy-pass-manager 指定用 legacy pass manager
hello.mm 只有 c /c++ 根本库女人

./clang -isysroot /Applications/Xcode.app/Contents/Developer/Platforms/iPhoneSimulator.platform/Developer/SDKs/iPhoneSimulator15.2.sdk -Xclang -load -Xclang ../lib/LLVMHello.dylib -flegacy-pass-manager hello.mm

-isysroot 指定零碎 sdk 版本
如果有用到 oc 的库编译还需指定 -framework Foundation

./clang -framework Foundation -isysroot /Applications/Xcode.app/Contents/Developer/Platforms/iPhoneSimulator.platform/Developer/SDKs/iPhoneSimulator15.2.sdk -Xclang -load -Xclang ../lib/LLVMHello.dylib -flegacy-pass-manager hello.m

hello.m 源码

#import <Foundation/Foundation.h>
#import <UIKit/UIKit.h>
int main(){NSLog(@"songxuhua");
  return 0;
}