通过IRBuilder新建LLVM IR

这一部分想给出一个完整的例子，来利用IRBuilder建立func_sum，并完成对齐的调用。（网上应该有完整的说明，忘记是哪里来的，留在这里方便记录，找到来源后附链接）来实现类似的功能：

int sum(int n){
  int i = 1;
  int sum = 0;
  while(i<=n){
    sum += i;
    i++;
  }
  return sum;
}

int main(){
  return sum(10);
}

相似功能不做更多介绍，代码和注释已经很明确。

#include "llvm/IR/LLVMContext.h"
#include "llvm/IR/Module.h"
#include "llvm/IR/Function.h"
#include "llvm/IR/BasicBlock.h"
#include "llvm/IR/IRBuilder.h"
#include "llvm/ExecutionEngine/MCJIT.h"
#include "llvm/Support/TargetSelect.h"
#include "llvm/IR/TypeBuilder.h"
#include "iostream"

using namespace llvm;
//c 

int main(){
  static LLVMContext MyGlobalContext;
  LLVMContext &context = MyGlobalContext;

  //Create a module
  Module *module = new Module("test", context);
  IRBuilder<> builder(context);

  //create a function
  FunctionType *sum_type = TypeBuilder<int(int), false>::get(context);
  Function *sum_fun = cast<Function>(module->getOrInsertFunction("sum", sum_type));

  //create function's args
  Function::arg_iterator argsIt = sum_fun->arg_begin();
  Value *arg_n = argsIt++;
  arg_n->setName("n");

  //create two constant value
  Value *const_0 = ConstantInt::get(IntegerType::getInt32Ty(context), 0);
  Value *const_1 = ConstantInt::get(IntegerType::getInt32Ty(context), 1);

  //create entry basicblock
  BasicBlock *entry_sum = BasicBlock::Create(context, "entry", sum_fun);
  builder.SetInsertPoint(entry_sum);

  //Create 3 while BasicBlock
  BasicBlock *while_count = BasicBlock::Create(context, 
  "while_count", sum_fun);
  BasicBlock *while_body = BasicBlock::Create(context, "while_body", sum_fun);
  BasicBlock *while_end = BasicBlock::Create(context, "while_end", sum_fun);


  //Create variable i & sum
  Value *i_alloc = builder.CreateAlloca(Type::getInt32Ty(context));
  Value *sum_alloc = builder.CreateAlloca(Type::getInt32Ty(context));
  builder.CreateStore(const_1, i_alloc);
  builder.CreateStore(const_0, sum_alloc);
  builder.CreateBr(while_count);

  //while_count
  builder.SetInsertPoint(while_count);
  Value *i_load = builder.CreateLoad(Type::getInt32Ty(context), i_alloc);
  Value *cmp_value = builder.CreateICmpSLE(i_load, arg_n);
  builder.CreateCondBr(cmp_value, while_body, while_end);

  //while_body
  builder.SetInsertPoint(while_body);
  Value *sum_load = builder.CreateLoad(Type::getInt32Ty(context), sum_alloc);
  Value *temp_sum = builder.CreateAdd(sum_load, i_load);
  builder.CreateStore(temp_sum, sum_alloc);
  Value *temp_i = builder.CreateAdd(i_load, const_1);
  builder.CreateStore(temp_i, i_alloc);
  builder.CreateBr(while_count);

  builder.SetInsertPoint(while_end);
  Value *ret_sum = builder.CreateLoad(Type::getInt32Ty(context), sum_alloc);
  builder.CreateRet(ret_sum);

  //Function Decalare: int main()
  FunctionType *main_type = TypeBuilder<int(), false>::get(context);
  Function *main_fun = cast<Function>(module->getOrInsertFunction("main", main_type));
  BasicBlock *entry_main = BasicBlock::Create(context, "entry", main_fun);
  Value *n_value = ConstantInt::get(Type::getInt32Ty(context), 10);

  std::vector<Value*> putsargs;
  putsargs.push_back(n_value);
  ArrayRef<Value*> argsRef(putsargs);
  builder.SetInsertPoint(entry_main);
  Value *ret_value = builder.CreateCall(sum_fun, argsRef);

  builder.CreateRet(ret_value);

  module->dump();

  InitializeNativeTarget();
  InitializeNativeTargetAsmPrinter();
  InitializeNativeTargetAsmParser();

  //Create ExecutionEngine
  ExecutionEngine *ee = EngineBuilder(std::unique_ptr<Module>(module)).setEngineKind(EngineKind::JIT).create();
  void *mainAddr = ee->getPointerToFunction(main_fun);

  //execute
  typedef int (*FuncType)();
  FuncType mainFunc = (FuncType)mainAddr;
  ee->finalizeObject();
  std::cout << mainFunc() << std::endl;

  delete module;
  return 0;
}

需要调用  clang++ -O3 IRBuilder.cpp -o irmain `llvm-config --cflags --ldflags` `llvm-config --libs` `llvm-config --system-libs`  进行编译