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/Transformsmkdir 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-projectcmake -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;}