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/ExecutionEngine/JIT.h"
  43 #include "llvm/ExecutionEngine/Interpreter.h"
  44 #include "llvm/ExecutionEngine/GenericValue.h"
  45 #include "llvm/Target/TargetSelect.h"
  46 #include "llvm/Support/ManagedStatic.h"
  47 #include "llvm/Support/raw_ostream.h"
  48 #include "llvm/Support/IRBuilder.h"
  49
  50 using namespace llvm;
  51
  52 int main() {
  53
  54   InitializeNativeTarget();
  55
  56   LLVMContext Context;
  57
  58   // Create some module to put our function into it.
  59   Module *M = new Module("test", Context);
  60
  61   // Create the add1 function entry and insert this entry into module M.  The
  62   // function will have a return type of "int" and take an argument of "int".
  63   // The '0' terminates the list of argument types.
  64   Function *Add1F =
  65     cast<Function>(M->getOrInsertFunction("add1", Type::getInt32Ty(Context),
  66                                           Type::getInt32Ty(Context),
  67                                           (Type *)0));
  68
  69   // Add a basic block to the function. As before, it automatically inserts
  70   // because of the last argument.
  71   BasicBlock *BB = BasicBlock::Create(Context, "EntryBlock", Add1F);
  72
  73   // Create a basic block builder with default parameters.  The builder will
  74   // automatically append instructions to the basic block `BB'.
  75   IRBuilder<> builder(BB);
  76
  77   // Get pointers to the constant `1'.
  78   Value *One = builder.getInt32(1);
  79
  80   // Get pointers to the integer argument of the add1 function...
  81   assert(Add1F->arg_begin() != Add1F->arg_end()); // Make sure there's an arg
  82   Argument *ArgX = Add1F->arg_begin();  // Get the arg
  83   ArgX->setName("AnArg");            // Give it a nice symbolic name for fun.
  84
  85   // Create the add instruction, inserting it into the end of BB.
  86   Value *Add = builder.CreateAdd(One, ArgX);
  87
  88   // Create the return instruction and add it to the basic block
  89   builder.CreateRet(Add);
  90
  91   // Now, function add1 is ready.
  92
  93
  94   // Now we're going to create function `foo', which returns an int and takes no
  95   // arguments.
  96   Function *FooF =
  97     cast<Function>(M->getOrInsertFunction("foo", Type::getInt32Ty(Context),
  98                                           (Type *)0));
  99
 100   // Add a basic block to the FooF function.
 101   BB = BasicBlock::Create(Context, "EntryBlock", FooF);
 102
 103   // Tell the basic block builder to attach itself to the new basic block
 104   builder.SetInsertPoint(BB);
 105
 106   // Get pointer to the constant `10'.
 107   Value *Ten = builder.getInt32(10);
 108
 109   // Pass Ten to the call to Add1F
 110   CallInst *Add1CallRes = builder.CreateCall(Add1F, Ten);
 111   Add1CallRes->setTailCall(true);
 112
 113   // Create the return instruction and add it to the basic block.
 114   builder.CreateRet(Add1CallRes);
 115
 116   // Now we create the JIT.
 117   ExecutionEngine* EE = EngineBuilder(M).create();
 118
 119   outs() << "We just constructed this LLVM module:\n\n" << *M;
 120   outs() << "\n\nRunning foo: ";
 121   outs().flush();
 122
 123   // Call the `foo' function with no arguments:
 124   std::vector<GenericValue> noargs;
 125   GenericValue gv = EE->runFunction(FooF, noargs);
 126
 127   // Import result of execution:
 128   outs() << "Result: " << gv.IntVal << "\n";
 129   EE->freeMachineCodeForFunction(FooF);
 130   delete EE;
 131   llvm_shutdown();
 132   return 0;
 133 }