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      1 //===--- examples/Fibonacci/fibonacci.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 build quickly a small module
     11 // with function Fibonacci and execute it with the JIT.
     12 //
     13 // The goal of this snippet is to create in the memory the LLVM module
     14 // consisting of one function as follow:
     15 //
     16 //   int fib(int x) {
     17 //     if(x<=2) return 1;
     18 //     return fib(x-1)+fib(x-2);
     19 //   }
     20 //
     21 // Once we have this, we compile the module via JIT, then execute the `fib'
     22 // function and return result to a driver, i.e. to a "host program".
     23 //
     24 //===----------------------------------------------------------------------===//
     25 
     26 #include "llvm/Analysis/Verifier.h"
     27 #include "llvm/ExecutionEngine/GenericValue.h"
     28 #include "llvm/ExecutionEngine/Interpreter.h"
     29 #include "llvm/ExecutionEngine/JIT.h"
     30 #include "llvm/IR/Constants.h"
     31 #include "llvm/IR/DerivedTypes.h"
     32 #include "llvm/IR/Instructions.h"
     33 #include "llvm/IR/LLVMContext.h"
     34 #include "llvm/IR/Module.h"
     35 #include "llvm/Support/TargetSelect.h"
     36 #include "llvm/Support/raw_ostream.h"
     37 using namespace llvm;
     38 
     39 static Function *CreateFibFunction(Module *M, LLVMContext &Context) {
     40   // Create the fib function and insert it into module M. This function is said
     41   // to return an int and take an int parameter.
     42   Function *FibF =
     43     cast<Function>(M->getOrInsertFunction("fib", Type::getInt32Ty(Context),
     44                                           Type::getInt32Ty(Context),
     45                                           (Type *)0));
     46 
     47   // Add a basic block to the function.
     48   BasicBlock *BB = BasicBlock::Create(Context, "EntryBlock", FibF);
     49 
     50   // Get pointers to the constants.
     51   Value *One = ConstantInt::get(Type::getInt32Ty(Context), 1);
     52   Value *Two = ConstantInt::get(Type::getInt32Ty(Context), 2);
     53 
     54   // Get pointer to the integer argument of the add1 function...
     55   Argument *ArgX = FibF->arg_begin();   // Get the arg.
     56   ArgX->setName("AnArg");            // Give it a nice symbolic name for fun.
     57 
     58   // Create the true_block.
     59   BasicBlock *RetBB = BasicBlock::Create(Context, "return", FibF);
     60   // Create an exit block.
     61   BasicBlock* RecurseBB = BasicBlock::Create(Context, "recurse", FibF);
     62 
     63   // Create the "if (arg <= 2) goto exitbb"
     64   Value *CondInst = new ICmpInst(*BB, ICmpInst::ICMP_SLE, ArgX, Two, "cond");
     65   BranchInst::Create(RetBB, RecurseBB, CondInst, BB);
     66 
     67   // Create: ret int 1
     68   ReturnInst::Create(Context, One, RetBB);
     69 
     70   // create fib(x-1)
     71   Value *Sub = BinaryOperator::CreateSub(ArgX, One, "arg", RecurseBB);
     72   CallInst *CallFibX1 = CallInst::Create(FibF, Sub, "fibx1", RecurseBB);
     73   CallFibX1->setTailCall();
     74 
     75   // create fib(x-2)
     76   Sub = BinaryOperator::CreateSub(ArgX, Two, "arg", RecurseBB);
     77   CallInst *CallFibX2 = CallInst::Create(FibF, Sub, "fibx2", RecurseBB);
     78   CallFibX2->setTailCall();
     79 
     80 
     81   // fib(x-1)+fib(x-2)
     82   Value *Sum = BinaryOperator::CreateAdd(CallFibX1, CallFibX2,
     83                                          "addresult", RecurseBB);
     84 
     85   // Create the return instruction and add it to the basic block
     86   ReturnInst::Create(Context, Sum, RecurseBB);
     87 
     88   return FibF;
     89 }
     90 
     91 
     92 int main(int argc, char **argv) {
     93   int n = argc > 1 ? atol(argv[1]) : 24;
     94 
     95   InitializeNativeTarget();
     96   LLVMContext Context;
     97 
     98   // Create some module to put our function into it.
     99   OwningPtr<Module> M(new Module("test", Context));
    100 
    101   // We are about to create the "fib" function:
    102   Function *FibF = CreateFibFunction(M.get(), Context);
    103 
    104   // Now we going to create JIT
    105   std::string errStr;
    106   ExecutionEngine *EE =
    107     EngineBuilder(M.get())
    108     .setErrorStr(&errStr)
    109     .setEngineKind(EngineKind::JIT)
    110     .create();
    111 
    112   if (!EE) {
    113     errs() << argv[0] << ": Failed to construct ExecutionEngine: " << errStr
    114            << "\n";
    115     return 1;
    116   }
    117 
    118   errs() << "verifying... ";
    119   if (verifyModule(*M)) {
    120     errs() << argv[0] << ": Error constructing function!\n";
    121     return 1;
    122   }
    123 
    124   errs() << "OK\n";
    125   errs() << "We just constructed this LLVM module:\n\n---------\n" << *M;
    126   errs() << "---------\nstarting fibonacci(" << n << ") with JIT...\n";
    127 
    128   // Call the Fibonacci function with argument n:
    129   std::vector<GenericValue> Args(1);
    130   Args[0].IntVal = APInt(32, n);
    131   GenericValue GV = EE->runFunction(FibF, Args);
    132 
    133   // import result of execution
    134   outs() << "Result: " << GV.IntVal << "\n";
    135 
    136   return 0;
    137 }
    138