1 //===-- examples/HowToUseJIT/HowToUseJIT.cpp - An example use of the JIT --===// 2 // 3 // The LLVM Compiler Infrastructure 4 // 5 // This file was developed by Valery A. Khamenya and is distributed under the 6 // University of Illinois Open Source License. See LICENSE.TXT for details. 7 // 8 //===----------------------------------------------------------------------===// 9 // 10 // This small program provides an example of how to quickly build a small 11 // module with two functions and execute it with the JIT. 12 // 13 // Goal: 14 // The goal of this snippet is to create in the memory 15 // the LLVM module consisting of two functions as follow: 16 // 17 // int add1(int x) { 18 // return x+1; 19 // } 20 // 21 // int foo() { 22 // return add1(10); 23 // } 24 // 25 // then compile the module via JIT, then execute the `foo' 26 // function and return result to a driver, i.e. to a "host program". 27 // 28 // Some remarks and questions: 29 // 30 // - could we invoke some code using noname functions too? 31 // e.g. evaluate "foo()+foo()" without fears to introduce 32 // conflict of temporary function name with some real 33 // existing function name? 34 // 35 //===----------------------------------------------------------------------===// 36 37 #include "llvm/Module.h" 38 #include "llvm/Constants.h" 39 #include "llvm/Type.h" 40 #include "llvm/Instructions.h" 41 #include "llvm/ModuleProvider.h" 42 #include "llvm/ExecutionEngine/ExecutionEngine.h" 43 #include "llvm/ExecutionEngine/GenericValue.h" 44 #include <iostream> 45 using namespace llvm; 46 47 int main() { 48 // Create some module to put our function into it. 49 Module *M = new Module("test"); 50 51 // Create the add1 function entry and insert this entry into module M. The 52 // function will have a return type of "int" and take an argument of "int". 53 // The '0' terminates the list of argument types. 54 Function *Add1F = M->getOrInsertFunction("add1", Type::IntTy, Type::IntTy, 0); 55 56 // Add a basic block to the function. As before, it automatically inserts 57 // because of the last argument. 58 BasicBlock *BB = new BasicBlock("EntryBlock", Add1F); 59 60 // Get pointers to the constant `1'. 61 Value *One = ConstantSInt::get(Type::IntTy, 1); 62 63 // Get pointers to the integer argument of the add1 function... 64 assert(Add1F->arg_begin() != Add1F->arg_end()); // Make sure there's an arg 65 Argument *ArgX = Add1F->arg_begin(); // Get the arg 66 ArgX->setName("AnArg"); // Give it a nice symbolic name for fun. 67 68 // Create the add instruction, inserting it into the end of BB. 69 Instruction *Add = BinaryOperator::createAdd(One, ArgX, "addresult", BB); 70 71 // Create the return instruction and add it to the basic block 72 new ReturnInst(Add, BB); 73 74 // Now, function add1 is ready. 75 76 77 // Now we going to create function `foo', which returns an int and takes no 78 // arguments. 79 Function *FooF = M->getOrInsertFunction("foo", Type::IntTy, 0); 80 81 // Add a basic block to the FooF function. 82 BB = new BasicBlock("EntryBlock", FooF); 83 84 // Get pointers to the constant `10'. 85 Value *Ten = ConstantSInt::get(Type::IntTy, 10); 86 87 // Pass Ten to the call call: 88 std::vector<Value*> Params; 89 Params.push_back(Ten); 90 CallInst *Add1CallRes = new CallInst(Add1F, Params, "add1", BB); 91 Add1CallRes->setTailCall(true); 92 93 // Create the return instruction and add it to the basic block. 94 new ReturnInst(Add1CallRes, BB); 95 96 // Now we create the JIT. 97 ExistingModuleProvider* MP = new ExistingModuleProvider(M); 98 ExecutionEngine* EE = ExecutionEngine::create(MP, false); 99 100 std::cout << "We just constructed this LLVM module:\n\n" << *M; 101 std::cout << "\n\nRunning foo: " << std::flush; 102 103 // Call the `foo' function with no arguments: 104 std::vector<GenericValue> noargs; 105 GenericValue gv = EE->runFunction(FooF, noargs); 106 107 // Import result of execution: 108 std::cout << "Result: " << gv.IntVal << "\n"; 109 return 0; 110 } 111