具有类型比较的 LLVM 测试示例问题

Question

我正在研究 LLVM Essentials 书中的一个示例。该部分称为 Emitting if-else condition IR，我不断收到以下错误。

Assertion failed: (getOperand(0)->getType() == getOperand(1)->getType() 
&& "Both operands to ICmp instruction are not of the same type!"),  
function AssertOK, 
file /usr/local/Cellar/llvm/3.6.2/include/llvm/IR/Instructions.h, line 
997. Abort trap: 6

我已经花了几个小时试图弄清楚这一点，但我无能为力。我敢肯定这是小事，但我不知道。我正在使用的代码如下。

#include "llvm/IR/IRBuilder.h"
#include "llvm/IR/LLVMContext.h"
#include "llvm/IR/Module.h"
#include "llvm/IR/Verifier.h"
#include <vector>
#include <iostream>
#include <typeinfo>
using namespace llvm;

static LLVMContext &Context = getGlobalContext();
static Module *ModuleOb = new Module("my compiler", Context);
static std::vector<std::string> FunArgs;
typedef SmallVector<BasicBlock *, 16> BBList;
typedef SmallVector<Value *, 16> ValList;

Function *createFunc(IRBuilder<> &Builder, std::string Name) {
  std::vector<Type *> Integers(FunArgs.size(), Type::getInt32Ty(Context));
  FunctionType *funcType =
      llvm::FunctionType::get(Builder.getInt32Ty(), Integers, false);
  Function *fooFunc = llvm::Function::Create(
      funcType, llvm::Function::ExternalLinkage, Name, ModuleOb);
  return fooFunc;
}

void setFuncArgs(Function *fooFunc, std::vector<std::string> FunArgs) {

  unsigned Idx = 0;
  Function::arg_iterator AI, AE;
  for (AI = fooFunc->arg_begin(), AE = fooFunc->arg_end(); AI != AE;
       ++AI, ++Idx)
    AI->setName(FunArgs[Idx]);
}

BasicBlock *createBB(Function *fooFunc, std::string Name) {
  return BasicBlock::Create(Context, Name, fooFunc);
}

GlobalVariable *createGlob(IRBuilder<> &Builder, std::string Name) {
  ModuleOb->getOrInsertGlobal(Name, Builder.getInt32Ty());
  GlobalVariable *gVar = ModuleOb->getNamedGlobal(Name);
  gVar->setLinkage(GlobalValue::CommonLinkage);
  gVar->setAlignment(4);
  return gVar;
}

Value *createArith(IRBuilder<> &Builder, Value *L, Value *R) {
  return Builder.CreateMul(L, R, "multmp");
}

Value *createIfElse(IRBuilder<> &Builder, BBList List, ValList VL) {
  Value *Condtn = VL[0];
  Value *Arg1 = VL[1];
  BasicBlock *ThenBB = List[0];
  BasicBlock *ElseBB = List[1];
  BasicBlock *MergeBB = List[2];
  Builder.CreateCondBr(Condtn, ThenBB, ElseBB);

  Builder.SetInsertPoint(ThenBB);
  Value *ThenVal = Builder.CreateAdd(Arg1, Builder.getInt32(1), "thenaddtmp");
  Builder.CreateBr(MergeBB);

  Builder.SetInsertPoint(ElseBB);
  Value *ElseVal = Builder.CreateAdd(Arg1, Builder.getInt32(2), "elseaddtmp");
  Builder.CreateBr(MergeBB);

  unsigned PhiBBSize = List.size() - 1;
  Builder.SetInsertPoint(MergeBB);
  PHINode *Phi = Builder.CreatePHI(Type::getInt32Ty(getGlobalContext()), PhiBBSize, "iftmp");
  Phi->addIncoming(ThenVal, ThenBB);
  Phi->addIncoming(ElseVal, ElseBB);

  return Phi;
}

int main(int argc, char *argv[]) {
  FunArgs.push_back("a");
  FunArgs.push_back("b");
  static IRBuilder<> Builder(Context);
  GlobalVariable *gVar = createGlob(Builder, "x");
  Function *fooFunc = createFunc(Builder, "foo");
  setFuncArgs(fooFunc, FunArgs);
  BasicBlock *entry = createBB(fooFunc, "entry");
  Builder.SetInsertPoint(entry);
  Value *Arg1 = fooFunc->arg_begin();
  Value *constant = Builder.getInt32(16);
  Value *val = createArith(Builder, Arg1, constant);

  Value *val2 = Builder.getInt32(100);
  Value *Compare = Builder.CreateICmpULT(val, val2, "cmptmp");
  Value *Condtn = Builder.CreateICmpNE(Compare, Builder.getInt32(0), "ifcond");
  ValList VL;
  VL.push_back(Condtn);
  VL.push_back(Arg1);

  BasicBlock *ThenBB = createBB(fooFunc, "then");
  BasicBlock *ElseBB = createBB(fooFunc, "else");
  BasicBlock *MergeBB = createBB(fooFunc, "ifcont");
  BBList List;
  List.push_back(ThenBB);
  List.push_back(ElseBB);
  List.push_back(MergeBB);

  Value *v = createIfElse(Builder, List, VL);

  Builder.CreateRet(v);
  verifyFunction(*fooFunc);
  ModuleOb->dump();
  return 0;
}

我知道这个位置出现了问题。我尝试将两者动态转换为相同的类型，但仍未编译。

Value *Condtn = Builder.CreateICmpNE(Compare, Builder.getInt32(0), "ifcond");

Answer 1

问题在于这两行：

Value *Compare = Builder.CreateICmpULT(val, val2, "cmptmp");
Value *Condtn = Builder.CreateICmpNE(Compare, Builder.getInt32(0), "ifcond");

第一条icmp 指令的计算结果为i1 类型的值，而您试图将其与i32 类型的值进行比较。

最好的办法是完全避免第二个icmp，因为它是多余的（它的计算结果与Compare 相同）。只需使用Compare 作为您的条件。

否则，您必须确保类型匹配——在这种情况下，您可以只使用Builder.getInt1(false) 而不是Builder.getInt32(0)。更一般地，您可以根据需要使用Builder.CreateIntCast 插入trunc 或zext 或sext 指令。