145 lines · cpp
1//===-- examples/HowToUseJIT/HowToUseJIT.cpp - An example use of the JIT --===//2//3// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.4// See https://llvm.org/LICENSE.txt for license information.5// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception6//7//===----------------------------------------------------------------------===//8//9// WARNING: This example demonstrates how to use LLVM's older ExecutionEngine10// JIT APIs. The newer LLJIT APIs should be preferred for new11// projects. See llvm/examples/HowToUseLLJIT.12//13// This small program provides an example of how to quickly build a small14// module with two functions and execute it with the JIT.15//16// Goal:17// The goal of this snippet is to create in the memory18// the LLVM module consisting of two functions as follow: 19//20// int add1(int x) {21// return x+1;22// }23//24// int foo() {25// return add1(10);26// }27//28// then compile the module via JIT, then execute the `foo'29// function and return result to a driver, i.e. to a "host program".30//31// Some remarks and questions:32//33// - could we invoke some code using noname functions too?34// e.g. evaluate "foo()+foo()" without fears to introduce35// conflict of temporary function name with some real36// existing function name?37//38//===----------------------------------------------------------------------===//39 40#include "llvm/ADT/STLExtras.h"41#include "llvm/ExecutionEngine/ExecutionEngine.h"42#include "llvm/ExecutionEngine/GenericValue.h"43#include "llvm/ExecutionEngine/MCJIT.h"44#include "llvm/IR/Argument.h"45#include "llvm/IR/BasicBlock.h"46#include "llvm/IR/Constants.h"47#include "llvm/IR/DerivedTypes.h"48#include "llvm/IR/Function.h"49#include "llvm/IR/IRBuilder.h"50#include "llvm/IR/Instructions.h"51#include "llvm/IR/LLVMContext.h"52#include "llvm/IR/Module.h"53#include "llvm/IR/Type.h"54#include "llvm/Support/Casting.h"55#include "llvm/Support/ManagedStatic.h"56#include "llvm/Support/TargetSelect.h"57#include "llvm/Support/raw_ostream.h"58#include <algorithm>59#include <cassert>60#include <memory>61#include <vector>62 63using namespace llvm;64 65int main() {66 InitializeNativeTarget();67 LLVMInitializeNativeAsmPrinter();68 69 LLVMContext Context;70 71 // Create some module to put our function into it.72 std::unique_ptr<Module> Owner = std::make_unique<Module>("test", Context);73 Module *M = Owner.get();74 75 // Create the add1 function entry and insert this entry into module M. The76 // function will have a return type of "int" and take an argument of "int".77 Function *Add1F =78 Function::Create(FunctionType::get(Type::getInt32Ty(Context),79 {Type::getInt32Ty(Context)}, false),80 Function::ExternalLinkage, "add1", M);81 82 // Add a basic block to the function. As before, it automatically inserts83 // because of the last argument.84 BasicBlock *BB = BasicBlock::Create(Context, "EntryBlock", Add1F);85 86 // Create a basic block builder with default parameters. The builder will87 // automatically append instructions to the basic block `BB'.88 IRBuilder<> builder(BB);89 90 // Get pointers to the constant `1'.91 Value *One = builder.getInt32(1);92 93 // Get pointers to the integer argument of the add1 function...94 assert(Add1F->arg_begin() != Add1F->arg_end()); // Make sure there's an arg95 Argument *ArgX = &*Add1F->arg_begin(); // Get the arg96 ArgX->setName("AnArg"); // Give it a nice symbolic name for fun.97 98 // Create the add instruction, inserting it into the end of BB.99 Value *Add = builder.CreateAdd(One, ArgX);100 101 // Create the return instruction and add it to the basic block102 builder.CreateRet(Add);103 104 // Now, function add1 is ready.105 106 // Now we're going to create function `foo', which returns an int and takes no107 // arguments.108 Function *FooF =109 Function::Create(FunctionType::get(Type::getInt32Ty(Context), {}, false),110 Function::ExternalLinkage, "foo", M);111 112 // Add a basic block to the FooF function.113 BB = BasicBlock::Create(Context, "EntryBlock", FooF);114 115 // Tell the basic block builder to attach itself to the new basic block116 builder.SetInsertPoint(BB);117 118 // Get pointer to the constant `10'.119 Value *Ten = builder.getInt32(10);120 121 // Pass Ten to the call to Add1F122 CallInst *Add1CallRes = builder.CreateCall(Add1F, Ten);123 Add1CallRes->setTailCall(true);124 125 // Create the return instruction and add it to the basic block.126 builder.CreateRet(Add1CallRes);127 128 // Now we create the JIT.129 ExecutionEngine* EE = EngineBuilder(std::move(Owner)).create();130 131 outs() << "We just constructed this LLVM module:\n\n" << *M;132 outs() << "\n\nRunning foo: ";133 outs().flush();134 135 // Call the `foo' function with no arguments:136 std::vector<GenericValue> noargs;137 GenericValue gv = EE->runFunction(FooF, noargs);138 139 // Import result of execution:140 outs() << "Result: " << gv.IntVal << "\n";141 delete EE;142 llvm_shutdown();143 return 0;144}145