1 //===-- examples/HowToUseJIT/HowToUseJIT.cpp - An example use of the JIT --===//
2 //
3 //                     The LLVM Compiler Infrastructure
4 //
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
7 //
8 //===----------------------------------------------------------------------===//
9 //
10 //  This small program provides an example of how to quickly build a small
11 //  module with two functions and execute it with the JIT.
12 //
13 // Goal:
14 //  The goal of this snippet is to create in the memory
15 //  the LLVM module consisting of two functions as follow:
16 //
17 // int add1(int x) {
18 //   return x+1;
19 // }
20 //
21 // int foo() {
22 //   return add1(10);
23 // }
24 //
25 // then compile the module via JIT, then execute the `foo'
26 // function and return result to a driver, i.e. to a "host program".
27 //
28 // Some remarks and questions:
29 //
30 // - could we invoke some code using noname functions too?
31 //   e.g. evaluate "foo()+foo()" without fears to introduce
32 //   conflict of temporary function name with some real
33 //   existing function name?
34 //
35 //===----------------------------------------------------------------------===//
36 
37 #include "llvm/LLVMContext.h"
38 #include "llvm/Module.h"
39 #include "llvm/Constants.h"
40 #include "llvm/DerivedTypes.h"
41 #include "llvm/Instructions.h"
42 #include "llvm/ModuleProvider.h"
43 #include "llvm/ExecutionEngine/JIT.h"
44 #include "llvm/ExecutionEngine/Interpreter.h"
45 #include "llvm/ExecutionEngine/GenericValue.h"
46 #include "llvm/Target/TargetSelect.h"
47 #include "llvm/Support/ManagedStatic.h"
48 #include "llvm/Support/raw_ostream.h"
49 using namespace llvm;
50 
51 int main() {
52 
53   InitializeNativeTarget();
54 
55   LLVMContext Context;
56 
57   // Create some module to put our function into it.
58   Module *M = new Module("test", Context);
59 
60   // Create the add1 function entry and insert this entry into module M.  The
61   // function will have a return type of "int" and take an argument of "int".
62   // The '0' terminates the list of argument types.
63   Function *Add1F =
64     cast<Function>(M->getOrInsertFunction("add1", Type::Int32Ty, Type::Int32Ty,
65                                           (Type *)0));
66 
67   // Add a basic block to the function. As before, it automatically inserts
68   // because of the last argument.
69   BasicBlock *BB = BasicBlock::Create("EntryBlock", Add1F);
70 
71   // Get pointers to the constant `1'.
72   Value *One = ConstantInt::get(Type::Int32Ty, 1);
73 
74   // Get pointers to the integer argument of the add1 function...
75   assert(Add1F->arg_begin() != Add1F->arg_end()); // Make sure there's an arg
76   Argument *ArgX = Add1F->arg_begin();  // Get the arg
77   ArgX->setName("AnArg");            // Give it a nice symbolic name for fun.
78 
79   // Create the add instruction, inserting it into the end of BB.
80   Instruction *Add = BinaryOperator::CreateAdd(One, ArgX, "addresult", BB);
81 
82   // Create the return instruction and add it to the basic block
83   ReturnInst::Create(Add, BB);
84 
85   // Now, function add1 is ready.
86 
87 
88   // Now we going to create function `foo', which returns an int and takes no
89   // arguments.
90   Function *FooF =
91     cast<Function>(M->getOrInsertFunction("foo", Type::Int32Ty, (Type *)0));
92 
93   // Add a basic block to the FooF function.
94   BB = BasicBlock::Create("EntryBlock", FooF);
95 
96   // Get pointers to the constant `10'.
97   Value *Ten = ConstantInt::get(Type::Int32Ty, 10);
98 
99   // Pass Ten to the call call:
100   CallInst *Add1CallRes = CallInst::Create(Add1F, Ten, "add1", BB);
101   Add1CallRes->setTailCall(true);
102 
103   // Create the return instruction and add it to the basic block.
104   ReturnInst::Create(Add1CallRes, BB);
105 
106   // Now we create the JIT.
107   ExecutionEngine* EE = EngineBuilder(M).create();
108 
109   outs() << "We just constructed this LLVM module:\n\n" << *M;
110   outs() << "\n\nRunning foo: ";
111   outs().flush();
112 
113   // Call the `foo' function with no arguments:
114   std::vector<GenericValue> noargs;
115   GenericValue gv = EE->runFunction(FooF, noargs);
116 
117   // Import result of execution:
118   outs() << "Result: " << gv.IntVal << "\n";
119   EE->freeMachineCodeForFunction(FooF);
120   delete EE;
121   llvm_shutdown();
122   return 0;
123 }
124