1 //===------- HowToUseLLJIT.cpp - An example use of ORC-based LLJIT --------===//
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 a 'add1' function and use of IRBuilder to create add & return
11 //  instructions.
12 //
13 // Goal:
14 //  The goal of this snippet is to create in the memory
15 //  the LLVM module consisting of a function as follow:
16 //
17 // int add1(int x) {
18 //   return x+1;
19 // }
20 //  add1(42);
21 //
22 // then compile the module via LLJIT, then execute the 'add1'
23 // function and return result to a driver, i.e. to a "host program".
24 //
25 //===----------------------------------------------------------------------===//
26 
27 #include "llvm/ExecutionEngine/Orc/LLJIT.h"
28 #include "llvm/IR/Function.h"
29 #include "llvm/IR/IRBuilder.h"
30 #include "llvm/IR/Module.h"
31 #include "llvm/Support/CommandLine.h"
32 #include "llvm/Support/InitLLVM.h"
33 #include "llvm/Support/TargetSelect.h"
34 #include "llvm/Support/raw_ostream.h"
35 
36 using namespace llvm;
37 using namespace llvm::orc;
38 
39 ExitOnError ExitOnErr;
40 
41 ThreadSafeModule createDemoModule() {
42   auto Context = std::make_unique<LLVMContext>();
43   auto M = std::make_unique<Module>("test", *Context);
44 
45   // Create the add1 function entry and insert this entry into module M.  The
46   // function will have a return type of "int" and take an argument of "int".
47   Function *Add1F =
48       Function::Create(FunctionType::get(Type::getInt32Ty(*Context),
49                                          {Type::getInt32Ty(*Context)}, false),
50                        Function::ExternalLinkage, "add1", M.get());
51 
52   // Add a basic block to the function. As before, it automatically inserts
53   // because of the last argument.
54   BasicBlock *BB = BasicBlock::Create(*Context, "EntryBlock", Add1F);
55 
56   // Create a basic block builder with default parameters.  The builder will
57   // automatically append instructions to the basic block `BB'.
58   IRBuilder<> builder(BB);
59 
60   // Get pointers to the constant `1'.
61   Value *One = builder.getInt32(1);
62 
63   // Get pointers to the integer argument of the add1 function...
64   assert(Add1F->arg_begin() != Add1F->arg_end()); // Make sure there's an arg
65   Argument *ArgX = &*Add1F->arg_begin();          // Get the arg
66   ArgX->setName("AnArg"); // Give it a nice symbolic name for fun.
67 
68   // Create the add instruction, inserting it into the end of BB.
69   Value *Add = builder.CreateAdd(One, ArgX);
70 
71   // Create the return instruction and add it to the basic block
72   builder.CreateRet(Add);
73 
74   return ThreadSafeModule(std::move(M), std::move(Context));
75 }
76 
77 int main(int argc, char *argv[]) {
78   // Initialize LLVM.
79   InitLLVM X(argc, argv);
80 
81   InitializeNativeTarget();
82   InitializeNativeTargetAsmPrinter();
83 
84   cl::ParseCommandLineOptions(argc, argv, "HowToUseLLJIT");
85   ExitOnErr.setBanner(std::string(argv[0]) + ": ");
86 
87   // Create an LLJIT instance.
88   auto J = ExitOnErr(LLJITBuilder().create());
89   auto M = createDemoModule();
90 
91   ExitOnErr(J->addIRModule(std::move(M)));
92 
93   // Look up the JIT'd function, cast it to a function pointer, then call it.
94   auto Add1Sym = ExitOnErr(J->lookup("add1"));
95   int (*Add1)(int) = (int (*)(int))Add1Sym.getAddress();
96 
97   int Result = Add1(42);
98   outs() << "add1(42) = " << Result << "\n";
99 
100   return 0;
101 }
102