从 LLVM 添加映射到C++ lambda

add mapping to C++ lambda from LLVM

本文关键字：C++ lambda 映射 LLVM 添加      更新时间：2023-10-16

我有一组包装C++方法调用的lambda，我想用LLVM调用它们。我的尝试似乎缺少一些东西，即使在声明类型并向 lambda 添加全局映射之后，我也会收到 LLVM 错误。重现我尝试过的最少代码是：

#include "llvm/ExecutionEngine/GenericValue.h"
#include "llvm/ExecutionEngine/Interpreter.h"
#include "llvm/IR/Constants.h"
#include "llvm/IR/IRBuilder.h"
#include "llvm/Support/ManagedStatic.h"
#include "llvm/Support/TargetSelect.h"
using namespace llvm;
int main() {
  InitializeNativeTarget();
  LLVMContext Context;
  std::unique_ptr<Module> Owner = make_unique<Module>("SomeModule", Context);
  Module *M = Owner.get();
  FunctionType *lambdaFT = FunctionType::get(Type::getInt32Ty(Context), false);
  Function *lambdaFN = Function::Create(lambdaFT, Function::ExternalLinkage, "lambda", Owner.get());
  //this is what the original question had
  //auto lambdaBody = []() { return 100; };
  //this is an edit after Johannes Schaub's answer
  int32_t ( *lambdaBody)() = +[]() { return 100; };
  Function *mainF = cast<Function>(M->getOrInsertFunction("main", Type::getInt32Ty(Context), (Type *) 0));
  BasicBlock *BB = BasicBlock::Create(Context, "EntryBlock", mainF);
  IRBuilder<> builder(BB);
  CallInst *lambdaRes = builder.CreateCall(lambdaFN, std::vector<Value *>(), "lambdaRetVar");
  builder.CreateRet(lambdaRes);
  ExecutionEngine *EE = EngineBuilder(std::move(Owner)).create();
  EE->addGlobalMapping(lambdaFN, &lambdaBody);
  outs() << "We just constructed this LLVM module:nn" << *M;
  outs() << "nnRunning main: ";
  std::vector<GenericValue> noargs;
  GenericValue gv = EE->runFunction(mainF, noargs);
  outs() << "Result: " << gv.IntVal << "n";
  llvm_shutdown();
  delete EE;
  return 0;
}

这将产生输出：

We just constructed this LLVM module:
; ModuleID = 'SomeModule'
declare i32 @lambda()
define i32 @main() {
EntryBlock:
  %lambdaRetVar = call i32 @lambda()
  ret i32 %lambdaRetVar
}
Running main: 
LLVM ERROR: Tried to execute an unknown external function: lambda

我做错了什么？使用 LLVM 3.7.0(标记不存在(

你的 lambda 主体是一个类。您必须传递其函数调用运算符的地址，您可以通过将其转换为函数指针：auto lambdaBody = +[]() { return 100; };并将其作为void*：EE->addGlobalMapping(lambdaFN, reinterpret_cast<void*>(lambdaBody)); 传递来实现。

Johannes Schaub关于

lambda的回答有所帮助，但事实证明addGlobalMapping并没有像我想的那样。还缺少一些东西。最重要的是：

EE->InstallLazyFunctionCreator([&](const std::string &fnName) -> void * {
    if (fnName == "lambda") { return reinterpret_cast<void *>(lambdaBody); }
    return nullptr;
  });

InstallLazyFunctionCreator 在无法解析函数时使用。它被调用为函数的名称，作为响应，如果未找到或要执行的函数，则返回nullptr。

以下是完整的代码清单，其中包含一些补充(并非全部需要(：

#include "llvm/ExecutionEngine/GenericValue.h"
#include "llvm/ExecutionEngine/Interpreter.h"
#include "llvm/ExecutionEngine/RTDyldMemoryManager.h"
//must include to avoid "JIT has not been linked in" when creating the ExecutionEngine - https://llvm.org/bugs/show_bug.cgi?id=22910
#include "llvm/ExecutionEngine/MCJIT.h"
#include "llvm/IR/Constants.h"
#include "llvm/IR/IRBuilder.h"
#include "llvm/Support/ManagedStatic.h"
#include "llvm/Support/TargetSelect.h"
#include <iostream>
using namespace llvm;
int proxy() { return 1000; }
int main() {
  InitializeNativeTarget();
  llvm::InitializeNativeTargetAsmPrinter();
  llvm::InitializeNativeTargetAsmParser();
  LLVMContext Context;
  std::unique_ptr<Module> Owner = make_unique<Module>("SomeModule", Context);
  Module *M = Owner.get();
  FunctionType *lambdaFT = FunctionType::get(Type::getInt32Ty(Context), false);
  Function *lambdaFN = Function::Create(lambdaFT, Function::ExternalLinkage, "lambda", Owner.get());
  int32_t ( *lambdaBody)() = +[]() { return 9099899; };
  assert(9099899 == lambdaBody()); //make sure we can call it
  Function *mainF = cast<Function>(M->getOrInsertFunction("main", Type::getInt32Ty(Context), (Type *) 0));
  BasicBlock *BB = BasicBlock::Create(Context, "EntryBlock", mainF);
  IRBuilder<> builder(BB);
  CallInst *lambdaRes = builder.CreateCall(lambdaFN, std::vector<Value *>(), "lambdaRetVar");
  builder.CreateRet(lambdaRes);
  EngineBuilder eb(std::move(Owner));
  std::unique_ptr<RTDyldMemoryManager> MM;
  std::string Error;
  ExecutionEngine *EE = eb.setEngineKind(EngineKind::JIT)
                          .setMCJITMemoryManager(std::move(MM))
                          .setErrorStr(&Error)
                          .setOptLevel(CodeGenOpt::None)
                          .setCodeModel(CodeModel::JITDefault)
                          .setRelocationModel(Reloc::Default)
                              //.setMArch(MArch)
                          .setMCPU(sys::getHostCPUName())
                              //.setMAttrs(MAttrs)
                          .create();
  std::cout << Error << std::endl;
  EE->InstallLazyFunctionCreator([&](const std::string &fnName) -> void * {
    if (fnName == "lambda") { return reinterpret_cast<void *>(lambdaBody); }
    return nullptr;
  });
  EE->finalizeObject();
  outs() << "We just constructed this LLVM module:nn" << *M;
  outs() << "nnRunning main: ";
  std::vector<GenericValue> noargs;
  GenericValue gv = EE->runFunction(mainF, noargs);
  outs() << "Result: " << gv.IntVal << "n";
  assert(gv.IntVal == 9099899);
  llvm_shutdown();
  delete EE;
  return 0;
}
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