examples/HowToUseJIT/HowToUseJIT.cpp

   1 //===-- examples/HowToUseJIT/HowToUseJIT.cpp - An example use of the JIT --===//
   2 //
   3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
   4 // See https://llvm.org/LICENSE.txt for license information.
   5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
   6 //
   7 //===----------------------------------------------------------------------===//
   8 //
   9 //  This small program provides an example of how to quickly build a small
  10 //  module with two functions and execute it with the JIT.
  11 //
  12 // Goal:
  13 //  The goal of this snippet is to create in the memory
  14 //  the LLVM module consisting of two functions as follow:
  15 //
  16 // int add1(int x) {
  17 //   return x+1;
  18 // }
  19 //
  20 // int foo() {
  21 //   return add1(10);
  22 // }
  23 //
  24 // then compile the module via JIT, then execute the `foo'
  25 // function and return result to a driver, i.e. to a "host program".
  26 //
  27 // Some remarks and questions:
  28 //
  29 // - could we invoke some code using noname functions too?
  30 //   e.g. evaluate "foo()+foo()" without fears to introduce
  31 //   conflict of temporary function name with some real
  32 //   existing function name?
  33 //
  34 //===----------------------------------------------------------------------===//
  35
  36 #include "llvm/ADT/STLExtras.h"
  37 #include "llvm/ExecutionEngine/ExecutionEngine.h"
  38 #include "llvm/ExecutionEngine/GenericValue.h"
  39 #include "llvm/IR/Argument.h"
  40 #include "llvm/IR/BasicBlock.h"
  41 #include "llvm/IR/Constants.h"
  42 #include "llvm/IR/DerivedTypes.h"
  43 #include "llvm/IR/Function.h"
  44 #include "llvm/IR/IRBuilder.h"
  45 #include "llvm/IR/Instructions.h"
  46 #include "llvm/IR/LLVMContext.h"
  47 #include "llvm/IR/Module.h"
  48 #include "llvm/IR/Type.h"
  49 #include "llvm/Support/Casting.h"
  50 #include "llvm/Support/ManagedStatic.h"
  51 #include "llvm/Support/TargetSelect.h"
  52 #include "llvm/Support/raw_ostream.h"
  53 #include <algorithm>
  54 #include <cassert>
  55 #include <memory>
  56 #include <vector>
  57
  58 using namespace llvm;
  59
  60 int main() {
  61   InitializeNativeTarget();
  62
  63   LLVMContext Context;
  64
  65   // Create some module to put our function into it.
  66   std::unique_ptr<Module> Owner = make_unique<Module>("test", Context);
  67   Module *M = Owner.get();
  68
  69   // Create the add1 function entry and insert this entry into module M.  The
  70   // function will have a return type of "int" and take an argument of "int".
  71   Function *Add1F =
  72       Function::Create(FunctionType::get(Type::getInt32Ty(Context),
  73                                          {Type::getInt32Ty(Context)}, false),
  74                        Function::ExternalLinkage, "add1", M);
  75
  76   // Add a basic block to the function. As before, it automatically inserts
  77   // because of the last argument.
  78   BasicBlock *BB = BasicBlock::Create(Context, "EntryBlock", Add1F);
  79
  80   // Create a basic block builder with default parameters.  The builder will
  81   // automatically append instructions to the basic block `BB'.
  82   IRBuilder<> builder(BB);
  83
  84   // Get pointers to the constant `1'.
  85   Value *One = builder.getInt32(1);
  86
  87   // Get pointers to the integer argument of the add1 function...
  88   assert(Add1F->arg_begin() != Add1F->arg_end()); // Make sure there's an arg
  89   Argument *ArgX = &*Add1F->arg_begin();          // Get the arg
  90   ArgX->setName("AnArg");            // Give it a nice symbolic name for fun.
  91
  92   // Create the add instruction, inserting it into the end of BB.
  93   Value *Add = builder.CreateAdd(One, ArgX);
  94
  95   // Create the return instruction and add it to the basic block
  96   builder.CreateRet(Add);
  97
  98   // Now, function add1 is ready.
  99
 100   // Now we're going to create function `foo', which returns an int and takes no
 101   // arguments.
 102   Function *FooF =
 103       Function::Create(FunctionType::get(Type::getInt32Ty(Context), {}, false),
 104                        Function::ExternalLinkage, "foo", M);
 105
 106   // Add a basic block to the FooF function.
 107   BB = BasicBlock::Create(Context, "EntryBlock", FooF);
 108
 109   // Tell the basic block builder to attach itself to the new basic block
 110   builder.SetInsertPoint(BB);
 111
 112   // Get pointer to the constant `10'.
 113   Value *Ten = builder.getInt32(10);
 114
 115   // Pass Ten to the call to Add1F
 116   CallInst *Add1CallRes = builder.CreateCall(Add1F, Ten);
 117   Add1CallRes->setTailCall(true);
 118
 119   // Create the return instruction and add it to the basic block.
 120   builder.CreateRet(Add1CallRes);
 121
 122   // Now we create the JIT.
 123   ExecutionEngine* EE = EngineBuilder(std::move(Owner)).create();
 124
 125   outs() << "We just constructed this LLVM module:\n\n" << *M;
 126   outs() << "\n\nRunning foo: ";
 127   outs().flush();
 128
 129   // Call the `foo' function with no arguments:
 130   std::vector<GenericValue> noargs;
 131   GenericValue gv = EE->runFunction(FooF, noargs);
 132
 133   // Import result of execution:
 134   outs() << "Result: " << gv.IntVal << "\n";
 135   delete EE;
 136   llvm_shutdown();
 137   return 0;
 138 }