c++ - 从 LLVM 添加到 C++ lambda 的映射

Question

我有一组包装 C++ 方法调用的 lambda，我想用 LLVM 调用它们。我的尝试似乎遗漏了一些东西，即使在声明了类型并将全局映射添加到 lambda 之后，我仍然收到 LLVM 错误。重现我尝试的最小代码是:

#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:\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;
}

这导致输出:

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(标签不存在)

Answer 1

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