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      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/Support/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 }
    134