如何在 LLVM 中编写自定义模块间传递？

Question

我通过扩展 FunctionPass class 在 LLVM 中编写了一个标准的 Analysis pass。一切似乎都有道理。

现在我想做的是写几个模块间通道，也就是说，允许我一次分析多个模块的通道。一个这样的传递的目的是构建整个应用程序的调用图。另一个这样的传递的目的是我有一个涉及函数调用及其参数的优化的想法。

我知道 LLVM 中的过程间传递，通过扩展 ModulePass class，但这只允许在单个模块内进行分析。

我知道 LLVM 中的 link time optimization (LTO)，但是 (a) 我不太清楚这是否是我想要的，并且 (b) 我没有找到关于如何实际写 LTO 通行证。

如何在 LLVM 中编写模块间通道，即可以访问应用程序中所有模块的通道？

Answer 1

我找到了一种方法来实现我的目标：编写一个简单的程序，使用 llvm::parseBitcodeFile() 读取一个 bitcode 文件并创建一个 Module 可以遍历和分析的对象。不太理想，因为它不是LLVM框架内可以运行的Pass。但是，它是实现我一次分析多个模块的目标的一种方法。

对于未来的读者，这是我所做的。

创建一个简单的工具来读取位码文件并生成 `Module`

//ReadBitcode.cpp
#include <iostream>
#include "llvm/IR/Module.h"
#include "llvm/Support/MemoryBuffer.h"
#include "llvm/Support/SourceMgr.h"
#include "llvm/IR/LLVMContext.h"
#include "llvm/Bitcode/ReaderWriter.h"

using namespace llvm;

int main(int argc, char *argv[])
{
    if (argc != 2)
    {
        std::cerr << "Usage: " << argv[0] << " bitcode_filename" << std::endl;
        return 1;
    }
    StringRef filename = argv[1];
    LLVMContext context;

    ErrorOr<std::unique_ptr<MemoryBuffer>> fileOrErr = MemoryBuffer::getFileOrSTDIN(filename);
    if (std::error_code ec = fileOrErr.getError())
    {
        std::cerr << "Error opening input file: " + ec.message() << std::endl;
        return 2;
    }

    ErrorOr<llvm::Module *> moduleOrErr = parseBitcodeFile(fileOrErr.get()->getMemBufferRef(), context);
    if (std::error_code ec = fileOrErr.getError())
    {
        std::cerr << "Error reading Module: " + ec.message() << std::endl;
        return 3;
    }

    Module *m = moduleOrErr.get();
    std::cout << "Successfully read Module:" << std::endl;
    std::cout << " Name: " << m->getName().str() << std::endl;
    std::cout << " Target triple: " << m->getTargetTriple() << std::endl;

    for (auto iter1 = m->getFunctionList().begin(); iter1 != m->getFunctionList().end(); iter1++)
    {
        Function &f = *iter1;
        std::cout << "  Function: " << f.getName().str() << std::endl;
        for (auto iter2 = f.getBasicBlockList().begin(); iter2 != f.getBasicBlockList().end();
             iter2++)
        {
            BasicBlock &bb = *iter2;
            std::cout << "    BasicBlock: " << bb.getName().str() << std::endl;
            for (auto iter3 = bb.begin(); iter3 != bb.end(); iter3++)
            {
                Instruction &i = *iter3;
                std::cout << "      Instruction: " << i.getOpcodeName() << std::endl;
            }
        }
    }
    return 0;
}

编译工具

$ clang++ ReadBitcode.cpp -o reader `llvm-config --cxxflags --libs --ldflags --system-libs`

创建一个位码文件进行分析

$ cat foo.c 
int my_fun(int arg1){
    int x = arg1;
    return x+1;
}

int main(){
    int a = 11;
    int b = 22;
    int c = 33;
    int d = 44;
    if (a > 10){
        b = c;
    } else {
        b = my_fun(d);
    }
    return b;
}

$ clang -emit-llvm -o foo.bc -c foo.c

运行`reader`工具上的bitcode

$ ./reader foo.bc
Successfully read Module:
 Name: foo.bc
 Target triple: x86_64-pc-linux-gnu
  Function: my_fun
    BasicBlock: 
      Instruction: alloca
      Instruction: alloca
      Instruction: store
      Instruction: load
      Instruction: store
      Instruction: load
      Instruction: add
      Instruction: ret
  Function: main
    BasicBlock: 
      Instruction: alloca
      Instruction: alloca
      Instruction: alloca
      Instruction: alloca
      Instruction: alloca
      Instruction: store
      Instruction: store
      Instruction: store
      Instruction: store
      Instruction: store
      Instruction: load
      Instruction: icmp
      Instruction: br
    BasicBlock: 
      Instruction: load
      Instruction: store
      Instruction: br
    BasicBlock: 
      Instruction: load
      Instruction: call
      Instruction: store
      Instruction: br
    BasicBlock: 
      Instruction: load
      Instruction: ret

Answer 2

这可以使用模块传递来完成。下面是我的代码，如果你需要帮助运行你可以看看 here.

bar.c

int your_fun(int arg2) {
    int x = arg2;
    return x+2;
}

Skeleton.cpp

#include "llvm/Pass.h"
#include "llvm/IR/Module.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 ModulePass {
    static char ID;
    SkeletonPass() : ModulePass(ID) {}

    virtual bool runOnModule(Module &M) {
        for (auto& F : M) {
            errs() << "\tFunction: " << F.getName() << "\n";

            for (auto& BB : F) {
                errs() << "\t\tBasic Block: " << BB.getName() << "\n";

                for (auto& I : BB) {
                    errs() << "\t\t\tInstruction: " << I.getOpcodeName() << "\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_ModuleOptimizerEarly,
                                                registerSkeletonPass);

static RegisterStandardPasses RegisterMyPass1(PassManagerBuilder::EP_EnabledOnOptLevel0,
                                                registerSkeletonPass);

输出：

| => clang -Xclang -load -Xclang build/skeleton/libSkeletonPass.so foo.c bar.c
Module: foo.c!
        Function: my_fun!
            Basicblock: entry!
            Instruction: alloca
            Instruction: alloca
            Instruction: store
            Instruction: load
            Instruction: store
            Instruction: load
            Instruction: add
            Instruction: ret
        Function: main!
            Basicblock: entry!
            Instruction: alloca
            Instruction: alloca
            Instruction: alloca
            Instruction: alloca
            Instruction: alloca
            Instruction: store
            Instruction: store
            Instruction: store
            Instruction: store
            Instruction: store
            Instruction: load
            Instruction: icmp
            Instruction: br
            Basicblock: if.then!
            Instruction: load
            Instruction: store
            Instruction: br
            Basicblock: if.else!
            Instruction: load
            Instruction: call
            Instruction: store
            Instruction: br
            Basicblock: if.end!
            Instruction: load
            Instruction: ret
Module: bar.c!
        Function: your_fun!
            Basicblock: entry!
            Instruction: alloca
            Instruction: alloca
            Instruction: store
            Instruction: load
            Instruction: store
            Instruction: load
            Instruction: add
            Instruction: ret

输出：如果包含链接到 bar.c

的头文件

Module: foo.c!
        Function: your_fun!
            Basicblock: entry!
            Instruction: alloca
            Instruction: alloca
            Instruction: store
            Instruction: load
            Instruction: store
            Instruction: load
            Instruction: add
            Instruction: ret
        Function: my_fun!
            Basicblock: entry!
            Instruction: alloca
            Instruction: alloca
            Instruction: store
            Instruction: load
            Instruction: store
            Instruction: load
            Instruction: add
            Instruction: ret
        Function: main!
            Basicblock: entry!
            Instruction: alloca
            Instruction: alloca
            Instruction: alloca
            Instruction: alloca
            Instruction: alloca
            Instruction: store
            Instruction: store
            Instruction: store
            Instruction: store
            Instruction: store
            Instruction: load
            Instruction: icmp
            Instruction: br
            Basicblock: if.then!
            Instruction: load
            Instruction: store
            Instruction: br
            Basicblock: if.else!
            Instruction: load
            Instruction: call
            Instruction: store
            Instruction: load
            Instruction: call
            Instruction: store
            Instruction: br
            Basicblock: if.end!
            Instruction: load
            Instruction: ret

Answer 3

在LTO中，所有模块都合并在一起，您可以在一个模块中看到整个程序IR。

您需要像编写任何模块通道一样编写模块通道，并将其添加到 PassManagerBuilder.cpp 中 populateLTOPassManager 函数中的 LTO 通道列表。这是 PassManagerBuilder 的文档： http://llvm.org/docs/doxygen/html/classllvm_1_1PassManagerBuilder.html

执行此操作时，您的通行证将与其他 LTO 通行证一起执行。

如何在 LLVM 中编写自定义模块间传递？

How to write a custom intermodular pass in LLVM?

llvm

static-analysis

llvm-ir

lto

创建一个简单的工具来读取位码文件并生成 `Module`

编译工具

创建一个位码文件进行分析

运行`reader`工具上的bitcode

如何在 LLVM 中编写自定义模块间传递？

How to write a custom intermodular pass in LLVM?

llvm

static-analysis

llvm-ir

lto

创建一个简单的工具来读取位码文件并生成 Module

编译工具

创建一个位码文件进行分析

运行reader工具上的bitcode

创建一个简单的工具来读取位码文件并生成 `Module`

运行`reader`工具上的bitcode