forked from OSchip/llvm-project
132 lines
4.4 KiB
C++
132 lines
4.4 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 is distributed under the University of Illinois Open Source
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// 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/LLVMContext.h"
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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/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 "llvm/Support/raw_ostream.h"
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#include "llvm/Target/TargetSelect.h"
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using namespace llvm;
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static Function *CreateFibFunction(Module *M, LLVMContext &Context) {
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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 =
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cast<Function>(M->getOrInsertFunction("fib", Type::getInt32Ty(Context),
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Type::getInt32Ty(Context),
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(Type *)0));
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// Add a basic block to the function.
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BasicBlock *BB = BasicBlock::Create(Context, "EntryBlock", FibF);
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// Get pointers to the constants.
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Value *One = ConstantInt::get(Type::getInt32Ty(Context), 1);
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Value *Two = ConstantInt::get(Type::getInt32Ty(Context), 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 = BasicBlock::Create(Context, "return", FibF);
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// Create an exit block.
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BasicBlock* RecurseBB = BasicBlock::Create(Context, "recurse", FibF);
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// Create the "if (arg <= 2) goto exitbb"
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Value *CondInst = new ICmpInst(*BB, ICmpInst::ICMP_SLE, ArgX, Two, "cond");
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BranchInst::Create(RetBB, RecurseBB, CondInst, BB);
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// Create: ret int 1
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ReturnInst::Create(Context, 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 = CallInst::Create(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 = CallInst::Create(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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ReturnInst::Create(Context, 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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InitializeNativeTarget();
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LLVMContext Context;
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// Create some module to put our function into it.
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Module *M = new Module("test", Context);
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// We are about to create the "fib" function:
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Function *FibF = CreateFibFunction(M, Context);
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// Now we going to create JIT
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std::string errStr;
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ExecutionEngine *EE = EngineBuilder(M).setErrorStr(&errStr).setEngineKind(EngineKind::JIT).create();
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if (!EE) {
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errs() << argv[0] << ": Failed to construct ExecutionEngine: " << errStr << "\n";
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return 1;
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}
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errs() << "verifying... ";
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if (verifyModule(*M)) {
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errs() << argv[0] << ": Error constructing function!\n";
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return 1;
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}
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errs() << "OK\n";
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errs() << "We just constructed this LLVM module:\n\n---------\n" << *M;
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errs() << "---------\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 = APInt(32, n);
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GenericValue GV = EE->runFunction(FibF, Args);
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// import result of execution
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outs() << "Result: " << GV.IntVal << "\n";
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return 0;
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}
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