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