Adding a simple example of how to use the JIT.

Contributed by Valery A. Khamenya. THANKS, Valery!

llvm-svn: 15622

llvm/projects/HowToUseJIT/HowToUseJIT.cpp

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+//===--- HowToUseJIT.cpp - An example use of the JIT ----------------------===//
+// 
+//                     The LLVM Compiler Infrastructure
+//
+// This file was developed by Valery A. Khamenya and is distributed under the
+// University of Illinois Open Source License. See LICENSE.TXT for details.
+// 
+//===----------------------------------------------------------------------===//
+//
+//  This tool provides a single point of access to the LLVM compilation tools.
+//  It has many options. To discover the options supported please refer to the
+//  tools' manual page (docs/CommandGuide/html/llvmc.html) or run the tool with
+//  the --help option.
+// 
+//===------------------------------------------------------------------------===
+
+// Goal: 
+//  The goal of this snippet is to create in the memory
+//  the LLVM module consisting of two functions as follow:
+//
+// int add1(int x) {
+//   return x+1;
+// }
+// 
+// int foo() {
+//   return add1(10);
+// }
+// 
+// then compile the module via JIT, then execute the `foo' 
+// function and return result to a driver, i.e. to a "host program".
+// 
+// Some remarks and questions:
+// 
+// - could we invoke some code using noname functions too?
+//   e.g. evaluate "foo()+foo()" without fears to introduce 
+//   conflict of temporary function name with some real
+//   existing function name?
+// 
+
+#include <iostream>
+
+#include <llvm/Module.h>
+#include <llvm/DerivedTypes.h>
+#include <llvm/Constants.h>
+#include <llvm/Instructions.h>
+#include <llvm/ModuleProvider.h>
+
+#include "llvm/ExecutionEngine/ExecutionEngine.h"
+#include "llvm/ExecutionEngine/GenericValue.h"
+
+
+using namespace llvm;
+
+int main() {
+
+  // Create some module to put our function into it.
+  Module *M = new Module("test");
+
+
+  // We are about to create the add1 function:
+  Function *Add1F;
+
+  {
+    // first create type for the single argument of add1 function: 
+    // the type is 'int ()'
+    std::vector<const Type*> ArgT(1);
+    ArgT[0] = Type::IntTy;
+
+    // now create full type of the add1 function:
+    FunctionType *Add1T = FunctionType::get(Type::IntTy, // type of result
+                                            ArgT,
+                                            /*not vararg*/false);
+ 
+    // Now create the add1 function entry and 
+    // insert this entry into module M
+    // (By passing a module as the last parameter to the Function constructor,
+    // it automatically gets appended to the Module.)
+    Add1F = new Function(Add1T, 
+                         Function::ExternalLinkage, // maybe too much
+                         "add1", M);
+
+    // Add a basic block to the function... (again, it automatically inserts
+    // because of the last argument.)
+    BasicBlock *BB = new BasicBlock("EntryBlock of add1 function", Add1F);
+  
+    // Get pointers to the constant `1'...
+    Value *One = ConstantSInt::get(Type::IntTy, 1);
+
+    // Get pointers to the integer argument of the add1 function...
+    assert(Add1F->abegin() != Add1F->aend()); // Make sure there's an arg
+    Argument &ArgX = Add1F->afront();  // Get the arg
+
+    // Create the add instruction... does not insert...
+    Instruction *Add = BinaryOperator::create(Instruction::Add, One, &ArgX,
+                                              "addresult");
+  
+    // explicitly insert it into the basic block...
+    BB->getInstList().push_back(Add);
+  
+    // Create the return instruction and add it to the basic block
+    BB->getInstList().push_back(new ReturnInst(Add));
+
+    // function add1 is ready
+  }
+
+
+  // now we going to create function `foo':
+  Function *FooF;
+
+  {  
+    // Create the foo function type:
+    FunctionType *FooT = 
+      FunctionType::get(Type::IntTy, // result has type: 'int ()'
+                        std::vector<const Type*>(), // no arguments
+                        /*not vararg*/false);
+    
+    // create the entry for function `foo' and insert
+    // this entry into module M:
+    FooF = 
+      new Function(FooT, 
+                   Function::ExternalLinkage, // too wide?
+                   "foo", M);
+    
+    // Add a basic block to the FooF function...
+    BasicBlock *BB = new BasicBlock("EntryBlock of add1 function", FooF);
+
+    // Get pointers to the constant `10'...
+    Value *Ten = ConstantSInt::get(Type::IntTy, 10);
+
+    // Put the argument Ten on stack and make call:
+    // ...
+    std::vector<Value*> Params;
+    Params.push_back(Ten);
+    CallInst * Add1CallRes = new CallInst(Add1F, Params, "add1", BB);
+    
+    // Create the return instruction and add it to the basic block
+    BB->getInstList().push_back(new ReturnInst(Add1CallRes));
+    
+  }
+
+  // Now we going to create JIT ??
+  ExistingModuleProvider* MP = new ExistingModuleProvider(M);
+  ExecutionEngine* EE = ExecutionEngine::create( MP, true );
+
+  // Call the `foo' function with no arguments:
+  std::vector<GenericValue> noargs;
+  GenericValue gv = EE->runFunction(FooF, noargs);
+
+  // import result of execution:
+  std::cout << "Result: " << gv.IntVal << std:: endl;
+
+  return 0;
+}

llvm/projects/HowToUseJIT/Makefile

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+##===- projects/HowToUseJIT/Makefile -----------------------*- Makefile -*-===##
+# 
+#                     The LLVM Compiler Infrastructure
+#
+# This file was developed by Valery A. Khamenya and is distributed under
+# the University of Illinois Open Source License. See LICENSE.TXT for details.
+# 
+##===----------------------------------------------------------------------===##
+LEVEL = ../..
+TOOLNAME = HowToUseJIT
+USEDLIBS = lli-jit lli-interpreter codegen executionengine x86 selectiondag \
+	   scalaropts analysis.a transformutils.a bcreader target.a vmcore \
+	   support.a
+
+include $(LEVEL)/Makefile.common