llvm for表达式

Posted 2021-06-02 Ajanuw

想要什么:

int fun(int p1)
{
  int r = 0;
  for(int i = 0; i < p1; i++)
  {
    r = r + i + p1;
  }
  return r;
}

IR:

define i32 @fun(i32 %p1) {
entry:
  %r = alloca i32, align 4
  store i32 0, i32* %r, align 4
  br label %loop

loop:                                             ; preds = %loopBody, %entry
  %i = phi i32 [ 0, %entry ], [ %3, %loopBody ]
  %0 = icmp slt i32 %i, %p1
  br i1 %0, label %loopBody, label %return

loopBody:                                         ; preds = %loop
  %1 = add i32 %i, %p1
  %r1 = load i32, i32* %r, align 4
  %2 = add i32 %r1, %1
  store i32 %2, i32* %r, align 4
  %3 = add i32 %i, 1
  br label %loop

return:                                           ; preds = %loop
  %r2 = load i32, i32* %r, align 4
  ret i32 %r2
}

#include "llvm/ExecutionEngine/Orc/LLJIT.h"
#include "llvm/IR/Function.h"
#include "llvm/IR/IRBuilder.h"
#include "llvm/IR/Module.h"
#include "llvm/Support/CommandLine.h"
#include "llvm/Support/InitLLVM.h"
#include "llvm/Support/TargetSelect.h"
#include "llvm/Support/raw_ostream.h"

using namespace llvm;
using namespace llvm::orc;

ExitOnError ExitOnErr;

ThreadSafeModule createTSM() {
  // context 拥有许多核心的 LLVM 数据结构，例如类型和常量值表
  auto Context = std::make_unique<LLVMContext>();

  // module 包含函数和全局变量的LLVM构造,它是 LLVM IR 用来包含代码的顶级结构。它将拥有我们生成的所有 IR 的内存
  auto M = std::make_unique<Module>("test", *Context);

  // 创建一个构建器，可以轻松生成 LLVM 指令
  IRBuilder<> builder(*Context);

  // 声明一个函数 int add1(int) 添加到module中
  auto funcType = FunctionType::get(Type::getInt32Ty(*Context), { Type::getInt32Ty(*Context) }, false);
  Function* Add1F = Function::Create(funcType, Function::ExternalLinkage, "fun", M.get());

  Argument* p1 = Add1F->getArg(0); // 获取参数
  p1->setName("p1"); // 设置arg name

  // 创建一个block添加到Add1F
  BasicBlock* BB = BasicBlock::Create(*Context, "entry", Add1F);

  // 构建器接下来的指令将插入到BB
  builder.SetInsertPoint(BB);
  
  // int r = 0
  auto r = builder.CreateAlloca(Type::getInt32Ty(*Context), 0, "r");
  builder.CreateStore(builder.getInt32(0), r);

  BasicBlock* LoopBB = BasicBlock::Create(*Context, "loop", Add1F);
  BasicBlock* LoopBodyBB = BasicBlock::Create(*Context, "loopBody", Add1F);
  BasicBlock* ReturnBB = BasicBlock::Create(*Context, "return", Add1F);

  builder.CreateBr(LoopBB);

  builder.SetInsertPoint(LoopBB);

  // i = 0
  auto i = builder.CreatePHI(Type::getInt32Ty(*Context), 2, "i");
  i->addIncoming(builder.getInt32(0), BB);

  // i < p1
  auto cmp = builder.CreateICmpSLT(i, p1); 
  builder.CreateCondBr(cmp, LoopBodyBB, ReturnBB );

  builder.SetInsertPoint(LoopBodyBB);
  
  // r = r + i + p1
  builder.CreateStore(
    builder.CreateAdd(builder.CreateLoad(r, "r"), builder.CreateAdd(i, p1)),
    r
  );

  // i++
  i->addIncoming(builder.CreateAdd(i, builder.getInt32(1)), LoopBodyBB);
  builder.CreateBr(LoopBB);
  
  // return r
  builder.SetInsertPoint(ReturnBB);
  builder.CreateRet(builder.CreateLoad(r, "r"));

  // 打印出所有生成的代码
  M->print(errs(), nullptr);

  // 返回线程模块
  return ThreadSafeModule(std::move(M), std::move(Context));
}

int main() {
  InitializeNativeTarget();
  InitializeNativeTargetAsmPrinter();

  // Create an LLJIT instance.
  auto _jit = ExitOnErr(LLJITBuilder().create());
  auto M = createTSM();

  ExitOnErr(_jit->addIRModule(std::move(M)));

  // 查找 JIT 函数，将其转换为函数指针，然后调用它.
  auto Add1Sym = ExitOnErr(_jit->lookup("fun"));
  int (*_fun)(int) = (int (*)(int))Add1Sym.getAddress();
  outs() << "fun(2) = " << _fun(2) << "\\n"; // 5

  return 0;
}

或者:

define i32 @fun(i32 %p1) {
entry:
  %r = alloca i32, align 4
  store i32 0, i32* %r, align 4
  %i = alloca i32, align 4
  store i32 0, i32* %i, align 4
  br label %loop

loop:                                             ; preds = %loopBody, %entry
  %0 = load i32, i32* %i, align 4
  %1 = icmp slt i32 %0, %p1
  br i1 %1, label %loopBody, label %return

loopBody:                                         ; preds = %loop
  %2 = load i32, i32* %i, align 4
  %3 = add i32 %2, %p1
  %r1 = load i32, i32* %r, align 4
  %4 = add i32 %r1, %3
  store i32 %4, i32* %r, align 4
  %5 = load i32, i32* %i, align 4
  %6 = add i32 %5, 1
  store i32 %6, i32* %i, align 4
  br label %loop

return:                                           ; preds = %loop
  %r2 = load i32, i32* %r, align 4
  ret i32 %r2
}

ThreadSafeModule createTSM() {
  ...
  
  // int r = 0
  auto r = builder.CreateAlloca(Type::getInt32Ty(*Context), 0, "r");
  builder.CreateStore(builder.getInt32(0), r);
  
  // int i = 0
  auto i = builder.CreateAlloca(Type::getInt32Ty(*Context), 0, "i");
  builder.CreateStore(builder.getInt32(0), i);

  BasicBlock* LoopBB = BasicBlock::Create(*Context, "loop", Add1F);
  BasicBlock* LoopBodyBB = BasicBlock::Create(*Context, "loopBody", Add1F);
  BasicBlock* ReturnBB = BasicBlock::Create(*Context, "return", Add1F);

  builder.CreateBr(LoopBB);

  builder.SetInsertPoint(LoopBB);

  // i < p1
  auto cmp = builder.CreateICmpSLT(builder.CreateLoad(i), p1);
  builder.CreateCondBr(cmp, LoopBodyBB, ReturnBB );

  builder.SetInsertPoint(LoopBodyBB);
  
  // r = r + i + p1
  builder.CreateStore(
    builder.CreateAdd(builder.CreateLoad(r, "r"), builder.CreateAdd(builder.CreateLoad(i), p1)),
    r
  );

  // i++
  builder.CreateStore(builder.CreateAdd(builder.CreateLoad(i), builder.getInt32(1)), i);
  builder.CreateBr(LoopBB);
  
  // return r
  builder.SetInsertPoint(ReturnBB);
  builder.CreateRet(builder.CreateLoad(r, "r"));

  // 打印出所有生成的代码
  M->print(errs(), nullptr);

  // 返回线程模块
  return ThreadSafeModule(std::move(M), std::move(Context));
}