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//===-- examples/HowToUseJIT/HowToUseJIT.cpp - An example use of the JIT --===//
// The LLVM Compiler Infrastructure
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
// This small program provides an example of how to quickly build a small
// module with two functions and execute it with the JIT.
// Goal:
// The goal of this snippet is to create in the memory
// the LLVM module consisting of two functions as follow:
// int add1(int x) {
// return x+1;
// }
// int foo() {
// return add1(10);
// }
// then compile the module via JIT, then execute the `foo'
// function and return result to a driver, i.e. to a "host program".
// Some remarks and questions:
// - could we invoke some code using noname functions too?
// e.g. evaluate "foo()+foo()" without fears to introduce
// conflict of temporary function name with some real
// existing function name?
#include "llvm/ADT/STLExtras.h"
#include "llvm/ExecutionEngine/ExecutionEngine.h"
#include "llvm/ExecutionEngine/GenericValue.h"
#include "llvm/IR/Argument.h"
#include "llvm/IR/BasicBlock.h"
#include "llvm/IR/Constants.h"
#include "llvm/IR/DerivedTypes.h"
#include "llvm/IR/Function.h"
#include "llvm/IR/IRBuilder.h"
#include "llvm/IR/Instructions.h"
#include "llvm/IR/LLVMContext.h"
#include "llvm/IR/Module.h"
#include "llvm/IR/Type.h"
#include "llvm/Support/Casting.h"
#include "llvm/Support/ManagedStatic.h"
#include "llvm/Support/TargetSelect.h"
#include "llvm/Support/raw_ostream.h"
#include <algorithm>
#include <cassert>
#include <memory>
#include <vector>
using namespace llvm;
int main() {
LLVMContext Context;
// Create some module to put our function into it.
std::unique_ptr<Module> Owner = make_unique<Module>("test", Context);
Module *M = Owner.get();
// Create the add1 function entry and insert this entry into module M. The
// function will have a return type of "int" and take an argument of "int".
Function *Add1F =
cast<Function>(M->getOrInsertFunction("add1", Type::getInt32Ty(Context),
// Add a basic block to the function. As before, it automatically inserts
// because of the last argument.
BasicBlock *BB = BasicBlock::Create(Context, "EntryBlock", Add1F);
// Create a basic block builder with default parameters. The builder will
// automatically append instructions to the basic block `BB'.
IRBuilder<> builder(BB);
// Get pointers to the constant `1'.
Value *One = builder.getInt32(1);
// Get pointers to the integer argument of the add1 function...
assert(Add1F->arg_begin() != Add1F->arg_end()); // Make sure there's an arg
Argument *ArgX = &*Add1F->arg_begin(); // Get the arg
ArgX->setName("AnArg"); // Give it a nice symbolic name for fun.
// Create the add instruction, inserting it into the end of BB.
Value *Add = builder.CreateAdd(One, ArgX);
// Create the return instruction and add it to the basic block
// Now, function add1 is ready.
// Now we're going to create function `foo', which returns an int and takes no
// arguments.
Function *FooF =
cast<Function>(M->getOrInsertFunction("foo", Type::getInt32Ty(Context)));
// Add a basic block to the FooF function.
BB = BasicBlock::Create(Context, "EntryBlock", FooF);
// Tell the basic block builder to attach itself to the new basic block
// Get pointer to the constant `10'.
Value *Ten = builder.getInt32(10);
// Pass Ten to the call to Add1F
CallInst *Add1CallRes = builder.CreateCall(Add1F, Ten);
// Create the return instruction and add it to the basic block.
// Now we create the JIT.
ExecutionEngine* EE = EngineBuilder(std::move(Owner)).create();
outs() << "We just constructed this LLVM module:\n\n" << *M;
outs() << "\n\nRunning foo: ";
// Call the `foo' function with no arguments:
std::vector<GenericValue> noargs;
GenericValue gv = EE->runFunction(FooF, noargs);
// Import result of execution:
outs() << "Result: " << gv.IntVal << "\n";
delete EE;
return 0;