139 lines
4.6 KiB
C++
139 lines
4.6 KiB
C++
//===-- examples/HowToUseJIT/HowToUseJIT.cpp - An example use of the JIT --===//
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//
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// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
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// See https://llvm.org/LICENSE.txt for license information.
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// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
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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 quickly build a small
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// module with two functions and execute it with the JIT.
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//
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// Goal:
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// The goal of this snippet is to create in the memory
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// the LLVM module consisting of two functions as follow:
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//
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// int add1(int x) {
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// return x+1;
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// }
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//
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// int foo() {
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// return add1(10);
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// }
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//
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// then compile the module via JIT, then execute the `foo'
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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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// Some remarks and questions:
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//
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// - could we invoke some code using noname functions too?
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// e.g. evaluate "foo()+foo()" without fears to introduce
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// conflict of temporary function name with some real
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// existing function name?
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//
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//===----------------------------------------------------------------------===//
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#include "llvm/ADT/STLExtras.h"
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#include "llvm/ExecutionEngine/ExecutionEngine.h"
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#include "llvm/ExecutionEngine/GenericValue.h"
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#include "llvm/IR/Argument.h"
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#include "llvm/IR/BasicBlock.h"
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#include "llvm/IR/Constants.h"
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#include "llvm/IR/DerivedTypes.h"
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#include "llvm/IR/Function.h"
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#include "llvm/IR/IRBuilder.h"
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#include "llvm/IR/Instructions.h"
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#include "llvm/IR/LLVMContext.h"
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#include "llvm/IR/Module.h"
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#include "llvm/IR/Type.h"
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#include "llvm/Support/Casting.h"
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#include "llvm/Support/ManagedStatic.h"
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#include "llvm/Support/TargetSelect.h"
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#include "llvm/Support/raw_ostream.h"
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#include <algorithm>
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#include <cassert>
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#include <memory>
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#include <vector>
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using namespace llvm;
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int main() {
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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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std::unique_ptr<Module> Owner = std::make_unique<Module>("test", Context);
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Module *M = Owner.get();
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// Create the add1 function entry and insert this entry into module M. The
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// function will have a return type of "int" and take an argument of "int".
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Function *Add1F =
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Function::Create(FunctionType::get(Type::getInt32Ty(Context),
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{Type::getInt32Ty(Context)}, false),
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Function::ExternalLinkage, "add1", M);
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// Add a basic block to the function. As before, it automatically inserts
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// because of the last argument.
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BasicBlock *BB = BasicBlock::Create(Context, "EntryBlock", Add1F);
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// Create a basic block builder with default parameters. The builder will
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// automatically append instructions to the basic block `BB'.
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IRBuilder<> builder(BB);
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// Get pointers to the constant `1'.
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Value *One = builder.getInt32(1);
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// Get pointers to the integer argument of the add1 function...
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assert(Add1F->arg_begin() != Add1F->arg_end()); // Make sure there's an arg
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Argument *ArgX = &*Add1F->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 add instruction, inserting it into the end of BB.
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Value *Add = builder.CreateAdd(One, ArgX);
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// Create the return instruction and add it to the basic block
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builder.CreateRet(Add);
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// Now, function add1 is ready.
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// Now we're going to create function `foo', which returns an int and takes no
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// arguments.
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Function *FooF =
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Function::Create(FunctionType::get(Type::getInt32Ty(Context), {}, false),
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Function::ExternalLinkage, "foo", M);
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// Add a basic block to the FooF function.
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BB = BasicBlock::Create(Context, "EntryBlock", FooF);
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// Tell the basic block builder to attach itself to the new basic block
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builder.SetInsertPoint(BB);
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// Get pointer to the constant `10'.
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Value *Ten = builder.getInt32(10);
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// Pass Ten to the call to Add1F
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CallInst *Add1CallRes = builder.CreateCall(Add1F, Ten);
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Add1CallRes->setTailCall(true);
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// Create the return instruction and add it to the basic block.
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builder.CreateRet(Add1CallRes);
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// Now we create the JIT.
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ExecutionEngine* EE = EngineBuilder(std::move(Owner)).create();
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outs() << "We just constructed this LLVM module:\n\n" << *M;
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outs() << "\n\nRunning foo: ";
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outs().flush();
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// Call the `foo' function with no arguments:
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std::vector<GenericValue> noargs;
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GenericValue gv = EE->runFunction(FooF, noargs);
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// Import result of execution:
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outs() << "Result: " << gv.IntVal << "\n";
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delete EE;
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llvm_shutdown();
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return 0;
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}
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