llvm example

test/runners/fibonacci.cpp

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+//===--- examples/Fibonacci/fibonacci.cpp - An example use of the JIT -----===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+// This small program provides an example of how to build quickly a small module
+// with function Fibonacci and execute it with the JIT.
+//
+// The goal of this snippet is to create in the memory the LLVM module
+// consisting of one function as follow:
+//
+//   int fib(int x) {
+//     if(x<=2) return 1;
+//     return fib(x-1)+fib(x-2);
+//   }
+//
+// Once we have this, we compile the module via JIT, then execute the `fib'
+// function and return result to a driver, i.e. to a "host program".
+//
+//===----------------------------------------------------------------------===//
+
+#include "llvm/LLVMContext.h"
+#include "llvm/Module.h"
+#include "llvm/DerivedTypes.h"
+#include "llvm/Constants.h"
+#include "llvm/Instructions.h"
+#include "llvm/Analysis/Verifier.h"
+#include "llvm/ExecutionEngine/JIT.h"
+#include "llvm/ExecutionEngine/Interpreter.h"
+#include "llvm/ExecutionEngine/GenericValue.h"
+#include "llvm/Support/raw_ostream.h"
+#include "llvm/Support/TargetSelect.h"
+using namespace llvm;
+
+static Function *CreateFibFunction(Module *M, LLVMContext &Context) {
+  // Create the fib function and insert it into module M.  This function is said
+  // to return an int and take an int parameter.
+  Function *FibF =
+    cast<Function>(M->getOrInsertFunction("fib", Type::getInt32Ty(Context),
+                                          Type::getInt32Ty(Context),
+                                          (Type *)0));
+
+  // Add a basic block to the function.
+  BasicBlock *BB = BasicBlock::Create(Context, "EntryBlock", FibF);
+
+  // Get pointers to the constants.
+  Value *One = ConstantInt::get(Type::getInt32Ty(Context), 1);
+  Value *Two = ConstantInt::get(Type::getInt32Ty(Context), 2);
+
+  // Get pointer to the integer argument of the add1 function...
+  Argument *ArgX = FibF->arg_begin();   // Get the arg.
+  ArgX->setName("AnArg");            // Give it a nice symbolic name for fun.
+
+  // Create the true_block.
+  BasicBlock *RetBB = BasicBlock::Create(Context, "return", FibF);
+  // Create an exit block.
+  BasicBlock* RecurseBB = BasicBlock::Create(Context, "recurse", FibF);
+
+  // Create the "if (arg <= 2) goto exitbb"
+  Value *CondInst = new ICmpInst(*BB, ICmpInst::ICMP_SLE, ArgX, Two, "cond");
+  BranchInst::Create(RetBB, RecurseBB, CondInst, BB);
+
+  // Create: ret int 1
+  ReturnInst::Create(Context, One, RetBB);
+
+  // create fib(x-1)
+  Value *Sub = BinaryOperator::CreateSub(ArgX, One, "arg", RecurseBB);
+  CallInst *CallFibX1 = CallInst::Create(FibF, Sub, "fibx1", RecurseBB);
+  CallFibX1->setTailCall();
+
+  // create fib(x-2)
+  Sub = BinaryOperator::CreateSub(ArgX, Two, "arg", RecurseBB);
+  CallInst *CallFibX2 = CallInst::Create(FibF, Sub, "fibx2", RecurseBB);
+  CallFibX2->setTailCall();
+
+
+  // fib(x-1)+fib(x-2)
+  Value *Sum = BinaryOperator::CreateAdd(CallFibX1, CallFibX2,
+                                         "addresult", RecurseBB);
+
+  // Create the return instruction and add it to the basic block
+  ReturnInst::Create(Context, Sum, RecurseBB);
+
+  return FibF;
+}
+
+
+int main(int argc, char **argv) {
+  int n = argc > 1 ? atol(argv[1]) : 24;
+
+  InitializeNativeTarget();
+  LLVMContext Context;
+
+  // Create some module to put our function into it.
+  OwningPtr<Module> M(new Module("test", Context));
+
+  // We are about to create the "fib" function:
+  Function *FibF = CreateFibFunction(M.get(), Context);
+
+  // Now we going to create JIT
+  std::string errStr;
+  ExecutionEngine *EE =
+    EngineBuilder(M.get())
+    .setErrorStr(&errStr)
+    .setEngineKind(EngineKind::JIT)
+    .create();
+
+  if (!EE) {
+    errs() << argv[0] << ": Failed to construct ExecutionEngine: " << errStr
+           << "\n";
+    return 1;
+  }
+
+  errs() << "verifying... ";
+  if (verifyModule(*M)) {
+    errs() << argv[0] << ": Error constructing function!\n";
+    return 1;
+  }
+
+  errs() << "OK\n";
+  errs() << "We just constructed this LLVM module:\n\n---------\n" << *M;
+  errs() << "---------\nstarting fibonacci(" << n << ") with JIT...\n";
+
+  // Call the Fibonacci function with argument n:
+  std::vector<GenericValue> Args(1);
+  Args[0].IntVal = APInt(32, n);
+  GenericValue GV = EE->runFunction(FibF, Args);
+
+  // import result of execution
+  outs() << "Result: " << GV.IntVal << "\n";
+
+  return 0;
+}