15

这可能是一些基本的东西，因为我刚刚开始学习 LLVM ..

下面创建一个阶乘函数并尝试 git 并执行它（我知道生成的 func 是正确的，因为我能够静态编译和执行它）。但是在执行函数时出现分段错误（在 EE->runFunction(TheF, Args) 中）

#include "llvm/Module.h"
#include "llvm/Function.h"
#include "llvm/PassManager.h"
#include "llvm/CallingConv.h"
#include "llvm/Analysis/Verifier.h"
#include "llvm/Assembly/PrintModulePass.h"
#include "llvm/Support/IRBuilder.h"
#include "llvm/Support/raw_ostream.h"
#include "llvm/ExecutionEngine/JIT.h"
#include "llvm/ExecutionEngine/GenericValue.h"


using namespace llvm;


Module* makeLLVMModule() {
  // Module Construction
  LLVMContext& ctx = getGlobalContext();
  Module* mod = new Module("test", ctx);
  Constant* c = mod->getOrInsertFunction("fact64",
  /*ret type*/                           IntegerType::get(ctx,64),
                                         IntegerType::get(ctx,64),
  /*varargs terminated with null*/       NULL);

  Function* fact64 = cast<Function>(c);
  fact64->setCallingConv(CallingConv::C);
  /* Arg names */
  Function::arg_iterator args = fact64->arg_begin();
  Value* x = args++;
  x->setName("x");


  /* Body */
  BasicBlock* block = BasicBlock::Create(ctx, "entry", fact64);
  BasicBlock* xLessThan2Block= BasicBlock::Create(ctx, "xlst2_block", fact64);
  BasicBlock* elseBlock = BasicBlock::Create(ctx, "else_block", fact64);
  IRBuilder<> builder(block);

  Value *One = ConstantInt::get(Type::getInt64Ty(ctx), 1);
  Value *Two = ConstantInt::get(Type::getInt64Ty(ctx), 2);

  Value* xLessThan2 = builder.CreateICmpULT(x, Two, "tmp");
 //builder.CreateCondBr(xLessThan2, xLessThan2Block, cond_false_2);
  builder.CreateCondBr(xLessThan2, xLessThan2Block, elseBlock);


  /* Recursion */
  builder.SetInsertPoint(elseBlock);
  Value* xMinus1 = builder.CreateSub(x, One, "tmp");
  std::vector<Value*> args1;
  args1.push_back(xMinus1);
  Value* recur_1 = builder.CreateCall(fact64, args1.begin(), args1.end(), "tmp");
  Value* retVal = builder.CreateBinOp(Instruction::Mul, x, recur_1, "tmp");
  builder.CreateRet(retVal);

  /* x<2 */
  builder.SetInsertPoint(xLessThan2Block);
  builder.CreateRet(One);
  return mod;
}

int main(int argc, char**argv) {
  long long x;
  if(argc > 1)
    x = atol(argv[1]);
  else
    x = 4;

  Module* Mod = makeLLVMModule();

  verifyModule(*Mod, PrintMessageAction);
  PassManager PM;
  PM.add(createPrintModulePass(&outs()));
  PM.run(*Mod);

  // Now we going to create JIT
  ExecutionEngine *EE = EngineBuilder(Mod).create();
  // Call the  function with argument x:
  std::vector<GenericValue> Args(1);
  Args[0].IntVal =  APInt(64, x);  
  Function* TheF = cast<Function>(Mod->getFunction("fact64"))  ;

  /* The following CRASHES.. */
  GenericValue GV = EE->runFunction(TheF, Args);
  outs() << "Result: " << GV.IntVal << "\n";
  delete Mod;
  return 0;
}

编辑： 启用 JIT 的正确方法（请参阅下面接受的答案）：

1.#include "llvm/ExecutionEngine/Jit.h"`

2.InitializeNativeTarget();
4

3 回答 3

11

我敢打赌 ExecutionEngine 指针为空......你错过了对 的调用InitializeNativeTarget，文档说：

InitializeNativeTarget - 主程序应该调用这个函数来初始化主机对应的原生目标。这对于 JIT 应用程序以确保正确链接目标很有用。

由于没有调用 InitializeNativeTarget 就没有可用的 JIT 编译器，ModuleBuilder 选择解释器（如果可用）。可能不是你想要的。你可能想看看我之前关于这个主题的帖子。

于 2010-03-16T02:50:16.707 回答
3 
#include "llvm/ExecutionEngine/Interpreter.h"
于 2010-03-13T14:59:27.713 回答
3

包含该标头 ( llvm/ExecutionEngine/Interpreter.h) 会强制 JIT 进行静态初始化。不是最好的设计决策，但至少它有效。

于 2010-03-14T10:45:37.737 回答