//===--- HowToUseJIT.cpp - An example use of the JIT ----------------------===//
// 
//                     The LLVM Compiler Infrastructure
//
// This file was developed by Valery A. Khamenya and is distributed under the
// University of Illinois Open Source License. See LICENSE.TXT for details.
// 
//===----------------------------------------------------------------------===//
//
//  This small program provides an example of how to quickly build a small
//  module with function Fibonacci and execute it with the JIT. 
//  (Modified from HowToUseJIT and Stacker/lib/compiler/StackerCompiler.cpp)
// 
//===------------------------------------------------------------------------===

// Goal: 
//  The goal of this snippet is to create in the memory
//  the LLVM module consisting of two functions as follow:
//
// int fib(int x) {
//   if(x<=2) return 1;
//   return fib(x-1)+fib(x-2);
// }
// 
// int foo() {
//   return fib(35);
// }
// 
// then compile the module via JIT, then execute the `foo' 
// function and return result to a driver, i.e. to a "host program".
// 
// Some remarks and questions:
// 
// - could we invoke some code using noname functions too?
//   e.g. evaluate "foo()+foo()" without fears to introduce 
//   conflict of temporary function name with some real
//   existing function name?
// 

#include <iostream>

#include <llvm/Module.h>
#include <llvm/DerivedTypes.h>
#include <llvm/Constants.h>
#include <llvm/Instructions.h>
#include <llvm/ModuleProvider.h>

#include "llvm/ExecutionEngine/ExecutionEngine.h"
#include "llvm/ExecutionEngine/GenericValue.h"


using namespace llvm;

int main(int argc, char**argv) {

  int n = argc > 1 ? atol(argv[1]) : 10;

  // Create some module to put our function into it.
  Module *M = new Module("test");


  // We are about to create the "fib" function:
  Function *FibF;

  {
    // first create type for the single argument of fib function: 
    // the type is 'int ()'
    std::vector<const Type*> ArgT(1);
    ArgT[0] = Type::IntTy;

    // now create full type of the "fib" function:
    FunctionType *FibT = FunctionType::get(Type::IntTy, // type of result
					   ArgT,
					   /*not vararg*/false);
 
    // Now create the fib function entry and 
    // insert this entry into module M
    // (By passing a module as the last parameter to the Function constructor,
    // it automatically gets appended to the Module.)
    FibF = new Function(FibT, 
			Function::ExternalLinkage, // maybe too much
			"fib", M);

    // Add a basic block to the function... (again, it automatically inserts
    // because of the last argument.)
    BasicBlock *BB = new BasicBlock("EntryBlock of fib function", FibF);
  
    // Get pointers to the constants ...
    Value *One = ConstantSInt::get(Type::IntTy, 1);
    Value *Two = ConstantSInt::get(Type::IntTy, 2);

    // Get pointers to the integer argument of the add1 function...
    assert(FibF->abegin() != FibF->aend()); // Make sure there's an arg

    Argument &ArgX = FibF->afront();  // Get the arg

    SetCondInst* CondInst 
      = new SetCondInst( Instruction::SetLE, &ArgX, Two );

    BB->getInstList().push_back(CondInst);

    // Create the true_block
    BasicBlock* true_bb = new BasicBlock("arg<=2");

    // Create the return instruction and add it 
    // to the basic block for true case:
    true_bb->getInstList().push_back(new ReturnInst(One));
      
    // Create an exit block
    BasicBlock* exit_bb = new BasicBlock("arg>2");
    
    {

      // create fib(x-1)
      CallInst * CallFibX1;
      {
	// Create the sub instruction... does not insert...
	Instruction *Sub = BinaryOperator::create(Instruction::Sub, &ArgX, One,
						"arg");
	exit_bb->getInstList().push_back(Sub);
	CallFibX1 = new CallInst(FibF, Sub, "fib(x-1)");
	exit_bb->getInstList().push_back(CallFibX1);
      }

      // create fib(x-2)
      CallInst * CallFibX2;
      {
	// Create the sub instruction... does not insert...
	Instruction *Sub = BinaryOperator::create(Instruction::Sub, &ArgX, Two,
						"arg");
	exit_bb->getInstList().push_back(Sub);
	CallFibX2 = new CallInst(FibF, Sub, "fib(x-2)");
	exit_bb->getInstList().push_back(CallFibX2);
      }

      // Create the add instruction... does not insert...
      Instruction *Add = 
	BinaryOperator::create(Instruction::Add, 
			       CallFibX1, CallFibX2, "addresult");
      
      // explicitly insert it into the basic block...
      exit_bb->getInstList().push_back(Add);
      
      // Create the return instruction and add it to the basic block
      exit_bb->getInstList().push_back(new ReturnInst(Add));      
    }

    // Create a branch on the SetCond
    BranchInst* br_inst = 
      new BranchInst( true_bb, exit_bb, CondInst );

    BB->getInstList().push_back( br_inst );
  }


  // now we going to create function `foo':
  Function *FooF;

  {  
    // Create the foo function type:
    FunctionType *FooT = 
      FunctionType::get(Type::IntTy, // result has type: 'int ()'
                        std::vector<const Type*>(), // no arguments
                        /*not vararg*/false);
    
    // create the entry for function `foo' and insert
    // this entry into module M:
    FooF = 
      new Function(FooT, 
                   Function::ExternalLinkage, // too wide?
                   "foo", M);
    
    // Add a basic block to the FooF function...
    BasicBlock *BB = new BasicBlock("EntryBlock of FooF function", FooF);

    // Get pointers to the constant ...
    Value *Const = ConstantSInt::get(Type::IntTy, n);

    // Put the argument Ten on stack and make call:
    // ...
    std::vector<Value*> Params;
    Params.push_back(Const);
    CallInst * FibFCallRes = new CallInst(FibF, Params, "call fib", BB);
    
    // Create the return instruction and add it to the basic block
    BB->getInstList().push_back(new ReturnInst(FibFCallRes));
    
  }

  // Now we going to create JIT ??
  ExistingModuleProvider* MP = new ExistingModuleProvider(M);
  ExecutionEngine* EE = ExecutionEngine::create( MP, true );

  // Call the `foo' function with no arguments:
  std::vector<GenericValue> noargs;
  GenericValue gv = EE->runFunction(FooF, noargs);

  // import result of execution:
  std::cout << "Result: " << gv.IntVal << std:: endl;

  return 0;
}
