從 LLVM 添加到 C++ lambda 的映射

Question

我有一組包含 C++ 方法調用的 lambda，我想用 LLVM 調用它們。 我的嘗試似乎遺漏了一些東西，即使在聲明類型並將全局映射添加到 lambda 之后，我仍然收到 LLVM 錯誤。 重現我嘗試過的最小代碼是：

#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:\n\n" << *M;
  outs() << "\n\nRunning main: ";

  std::vector<GenericValue> noargs;
  GenericValue gv = EE->runFunction(mainF, noargs);

  outs() << "Result: " << gv.IntVal << "\n";
  llvm_shutdown();
  delete EE;
  return 0;
}

這導致輸出：

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

我究竟做錯了什么？ 使用 LLVM 3.7.0 （標簽不存在）

Answer 1

你的 lambda 體是一個類。 您必須傳遞其函數調用運算符的地址，您可以通過將其轉換為函數指針來實現： auto lambdaBody = +[]() { return 100; }; auto lambdaBody = +[]() { return 100; }; 並將其作為void*傳遞： EE->addGlobalMapping(lambdaFN, reinterpret_cast<void*>(lambdaBody)); .

Answer 2

Johannes Schaub對 lambda 的回答有所幫助，但事實證明addGlobalMapping並沒有按照我的想法addGlobalMapping 。 還有一些東西不見了。 最重要的是：

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

當無法解析函數時使用InstallLazyFunctionCreator 。 它使用函數的名稱調用，作為響應，如果未找到或要執行的函數，該函數將返回nullptr 。

這是完整的代碼清單，並添加了一些內容（並非全部必需）：

#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:\n\n" << *M;
  outs() << "\n\nRunning 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;
}