examples/HowToUseJIT/HowToUseJIT.cpp

   1 //===-- examples/HowToUseJIT/HowToUseJIT.cpp - An example use of the JIT --===//
   2 //
   3 //                     The LLVM Compiler Infrastructure
   4 //
   5 // This file is distributed under the University of Illinois Open Source
   6 // 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/DerivedTypes.h"
  40 #include "llvm/Instructions.h"
  41 #include "llvm/ModuleProvider.h"
  42 #include "llvm/ExecutionEngine/JIT.h"
  43 #include "llvm/ExecutionEngine/Interpreter.h"
  44 #include "llvm/ExecutionEngine/GenericValue.h"
  45 #include "llvm/Support/ManagedStatic.h"
  46 #include "llvm/Support/raw_ostream.h"
  47 using namespace llvm;
  48
  49 int main() {
  50   // Create some module to put our function into it.
  51   Module *M = new Module("test");
  52
  53   // Create the add1 function entry and insert this entry into module M.  The
  54   // function will have a return type of "int" and take an argument of "int".
  55   // The '0' terminates the list of argument types.
  56   Function *Add1F =
  57     cast<Function>(M->getOrInsertFunction("add1", Type::Int32Ty, Type::Int32Ty,
  58                                           (Type *)0));
  59
  60   // Add a basic block to the function. As before, it automatically inserts
  61   // because of the last argument.
  62   BasicBlock *BB = BasicBlock::Create("EntryBlock", Add1F);
  63
  64   // Get pointers to the constant `1'.
  65   Value *One = ConstantInt::get(Type::Int32Ty, 1);
  66
  67   // Get pointers to the integer argument of the add1 function...
  68   assert(Add1F->arg_begin() != Add1F->arg_end()); // Make sure there's an arg
  69   Argument *ArgX = Add1F->arg_begin();  // Get the arg
  70   ArgX->setName("AnArg");            // Give it a nice symbolic name for fun.
  71
  72   // Create the add instruction, inserting it into the end of BB.
  73   Instruction *Add = BinaryOperator::CreateAdd(One, ArgX, "addresult", BB);
  74
  75   // Create the return instruction and add it to the basic block
  76   ReturnInst::Create(Add, BB);
  77
  78   // Now, function add1 is ready.
  79
  80
  81   // Now we going to create function `foo', which returns an int and takes no
  82   // arguments.
  83   Function *FooF =
  84     cast<Function>(M->getOrInsertFunction("foo", Type::Int32Ty, (Type *)0));
  85
  86   // Add a basic block to the FooF function.
  87   BB = BasicBlock::Create("EntryBlock", FooF);
  88
  89   // Get pointers to the constant `10'.
  90   Value *Ten = ConstantInt::get(Type::Int32Ty, 10);
  91
  92   // Pass Ten to the call call:
  93   CallInst *Add1CallRes = CallInst::Create(Add1F, Ten, "add1", BB);
  94   Add1CallRes->setTailCall(true);
  95
  96   // Create the return instruction and add it to the basic block.
  97   ReturnInst::Create(Add1CallRes, BB);
  98
  99   // Now we create the JIT.
 100   ExistingModuleProvider* MP = new ExistingModuleProvider(M);
 101   ExecutionEngine* EE = ExecutionEngine::create(MP, false);
 102
 103   outs() << "We just constructed this LLVM module:\n\n" << *M;
 104   outs() << "\n\nRunning foo: ";
 105   outs().flush();
 106
 107   // Call the `foo' function with no arguments:
 108   std::vector<GenericValue> noargs;
 109   GenericValue gv = EE->runFunction(FooF, noargs);
 110
 111   // Import result of execution:
 112   outs() << "Result: " << gv.IntVal << "\n";
 113   EE->freeMachineCodeForFunction(FooF);
 114   delete EE;
 115   llvm_shutdown();
 116   return 0;
 117 }