(pascal   03-Sep-16) 

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: //===-- examples/HowToUseJIT/HowToUseJIT.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 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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: 

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: #include "llvm/ADT/STLExtras.h"

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: #include "llvm/ExecutionEngine/GenericValue.h"

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: #include "llvm/ExecutionEngine/Interpreter.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/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/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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: 

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: using namespace llvm;

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: 

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: int main() {

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:   

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:   InitializeNativeTarget();

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: 

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:   LLVMContext Context;

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:   

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:   // Create some module to put our function into it.

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:   std::unique_ptr<Module> Owner = make_unique<Module>("test", Context);

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:   Module *M = Owner.get();

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: 

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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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:   // The '0' terminates the list of argument types.

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:   Function *Add1F =

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:     cast<Function>(M->getOrInsertFunction("add1", Type::getInt32Ty(Context),

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:                                           Type::getInt32Ty(Context),

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:                                           nullptr));

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: 

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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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: 

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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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: 

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:   // Get pointers to the constant `1'.

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:   Value *One = builder.getInt32(1);

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: 

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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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: 

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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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: 

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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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: 

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:   // Now, function add1 is ready.

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: 

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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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:     cast<Function>(M->getOrInsertFunction("foo", Type::getInt32Ty(Context),

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:                                           nullptr));

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: 

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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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: 

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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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: 

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:   // Get pointer to the constant `10'.

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:   Value *Ten = builder.getInt32(10);

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: 

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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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: 

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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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: 

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:   // Now we create the JIT.

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:   ExecutionEngine* EE = EngineBuilder(std::move(Owner)).create();

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: 

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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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: 

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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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: 

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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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: }