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/LLVMContext.h"
  38 #include "llvm/Module.h"
  39 #include "llvm/Constants.h"
  40 #include "llvm/DerivedTypes.h"
  41 #include "llvm/Instructions.h"
  42 #include "llvm/ModuleProvider.h"
  43 #include "llvm/ExecutionEngine/JIT.h"
  44 #include "llvm/ExecutionEngine/Interpreter.h"
  45 #include "llvm/ExecutionEngine/GenericValue.h"
  46 #include "llvm/Target/TargetSelect.h"
  47 #include "llvm/Support/ManagedStatic.h"
  48 #include "llvm/Support/raw_ostream.h"
  49 using namespace llvm;
  50
  51 int main() {
  52
  53   InitializeNativeTarget();
  54
  55   LLVMContext Context;
  56
  57   // Create some module to put our function into it.
  58   Module *M = new Module("test", Context);
  59
  60   // Create the add1 function entry and insert this entry into module M.  The
  61   // function will have a return type of "int" and take an argument of "int".
  62   // The '0' terminates the list of argument types.
  63   Function *Add1F =
  64     cast<Function>(M->getOrInsertFunction("add1", Type::getInt32Ty(Context),
  65                                           Type::getInt32Ty(Context),
  66                                           (Type *)0));
  67
  68   // Add a basic block to the function. As before, it automatically inserts
  69   // because of the last argument.
  70   BasicBlock *BB = BasicBlock::Create(Context, "EntryBlock", Add1F);
  71
  72   // Get pointers to the constant `1'.
  73   Value *One = ConstantInt::get(Type::getInt32Ty(Context), 1);
  74
  75   // Get pointers to the integer argument of the add1 function...
  76   assert(Add1F->arg_begin() != Add1F->arg_end()); // Make sure there's an arg
  77   Argument *ArgX = Add1F->arg_begin();  // Get the arg
  78   ArgX->setName("AnArg");            // Give it a nice symbolic name for fun.
  79
  80   // Create the add instruction, inserting it into the end of BB.
  81   Instruction *Add = BinaryOperator::CreateAdd(One, ArgX, "addresult", BB);
  82
  83   // Create the return instruction and add it to the basic block
  84   ReturnInst::Create(Context, Add, BB);
  85
  86   // Now, function add1 is ready.
  87
  88
  89   // Now we going to create function `foo', which returns an int and takes no
  90   // arguments.
  91   Function *FooF =
  92     cast<Function>(M->getOrInsertFunction("foo", Type::getInt32Ty(Context),
  93                                           (Type *)0));
  94
  95   // Add a basic block to the FooF function.
  96   BB = BasicBlock::Create(Context, "EntryBlock", FooF);
  97
  98   // Get pointers to the constant `10'.
  99   Value *Ten = ConstantInt::get(Type::getInt32Ty(Context), 10);
 100
 101   // Pass Ten to the call call:
 102   CallInst *Add1CallRes = CallInst::Create(Add1F, Ten, "add1", BB);
 103   Add1CallRes->setTailCall(true);
 104
 105   // Create the return instruction and add it to the basic block.
 106   ReturnInst::Create(Context, Add1CallRes, BB);
 107
 108   // Now we create the JIT.
 109   ExecutionEngine* EE = EngineBuilder(M).create();
 110
 111   outs() << "We just constructed this LLVM module:\n\n" << *M;
 112   outs() << "\n\nRunning foo: ";
 113   outs().flush();
 114
 115   // Call the `foo' function with no arguments:
 116   std::vector<GenericValue> noargs;
 117   GenericValue gv = EE->runFunction(FooF, noargs);
 118
 119   // Import result of execution:
 120   outs() << "Result: " << gv.IntVal << "\n";
 121   EE->freeMachineCodeForFunction(FooF);
 122   delete EE;
 123   llvm_shutdown();
 124   return 0;
 125 }