[llvm-commits] [llvm] r43200 - in /llvm/trunk/docs/tutorial: ./ Tutorial1.html index.html
Owen Anderson
resistor at mac.com
Fri Oct 19 22:23:07 PDT 2007
Author: resistor
Date: Sat Oct 20 00:23:06 2007
New Revision: 43200
URL: http://llvm.org/viewvc/llvm-project?rev=43200&view=rev
Log:
Add the beginnings of an LLVM tutorial. If anyone has suggestions, comments,
or would like to contribute, let me know!
Added:
llvm/trunk/docs/tutorial/
llvm/trunk/docs/tutorial/Tutorial1.html
llvm/trunk/docs/tutorial/index.html
Added: llvm/trunk/docs/tutorial/Tutorial1.html
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/docs/tutorial/Tutorial1.html?rev=43200&view=auto
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--- llvm/trunk/docs/tutorial/Tutorial1.html (added)
+++ llvm/trunk/docs/tutorial/Tutorial1.html Sat Oct 20 00:23:06 2007
@@ -0,0 +1,175 @@
+<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN"
+ "http://www.w3.org/TR/html4/strict.dtd">
+
+<html>
+<head>
+ <title>LLVM Tutorial 1: A First Function</title>
+ <meta http-equiv="Content-Type" content="text/html; charset=utf-8">
+ <meta name="author" content="Owen Anderson">
+ <meta name="description"
+ content="LLVM Tutorial 1: A First Function.">
+ <link rel="stylesheet" href="../llvm.css" type="text/css">
+</head>
+
+<body>
+
+<div class="doc_title"> LLVM Tutorial 1: A First Function </div>
+
+<div class="doc_author">
+ <p>Written by <a href="mailto:owen at apple.com">Owen Anderson</a></p>
+</div>
+
+<div class="doc_text">
+
+<p>For starters, lets consider a relatively straightforward function that takes three integer parameters and returns an arithmetic combination of them. This is nice and simple, especially since it involves no control flow:</p>
+
+<div class="doc_code">
+<pre>
+ int mul_add(int x, int y, int z) {
+ return x * y + z;
+ }
+</pre>
+</div>
+
+<p>As a preview, the LLVM IR weâre going to end up generating for this function will look like:</p>
+
+<div class="doc_code">
+<pre>
+ define i32 @mul_add(i32 %x, i32 %y, i32 %z) {
+ entry:
+ %tmp = mul i32 %x, %y
+ %tmp2 = add i32 %tmp, %z
+ ret i32 %tmp2
+ }
+</pre>
+</div>
+
+<p>Before going any further in this tutorial, you should look through the <a href="../LangRef.html">LLVM Language Reference Manual</a> and convince yourself that the above LLVM IR is actually equivalent to the original function. Once youâre satisfied with that, letâs move on to actually generating it programmatically!</p>
+
+<p>... STUFF ABOUT HEADERS ... </p>
+
+<p>Now, letâs get started on our real program. Hereâs what our basic <code>main()</code> will look like:</p>
+
+<div class="doc_code">
+<pre>
+using namespace llvm;
+
+Module* makeLLVMModule();
+
+int main(int argc, char**argv) {
+ Module* Mod = makeLLVMModule();
+
+ verifyModule(*Mod, PrintMessageAction);
+
+ PassManager PM;
+ PM.add(new PrintModulePass(&llvm::cout));
+ PM.run(*Mod);
+
+ return 0;
+}
+</pre>
+</div>
+
+<p>The first segment is pretty simple: it creates an LLVM âmodule.â In LLVM, a module represents a single unit of code that is to be processed together. A module contains things like global variables and function declarations and implementations. Here, weâve declared a <code>makeLLVMModule()</code> function to do the real work of creating the module. Donât worry, weâll be looking at that one next!</p>
+
+<p>The second segment runs the LLVM module verifier on our newly created module. While this probably isnât really necessary for a simple module like this one, itâs always a good idea, especially if youâre generating LLVM IR based on some input. The verifier will print an error message if your LLVM module is malformed in any way.</p>
+
+<p>Finally, we instantiate an LLVM <code>PassManager</code> and run the <code>PrintModulePass</code> on our module. LLVM uses an explicit pass infrastructure to manage optimizations and various other things. A <code>PassManager</code>, as should be obvious from its name, manages passes: it is responsible for scheduling them, invoking them, and insuring the proper disposal after weâre done with them. For this example, weâre just using a trivial pass that prints out our module in textual form.</p>
+
+<p>Now onto the interesting part: creating a populating a module. Hereâs the first chunk of our <code>createLLVMModule()</code>:</p>
+
+<div class="doc_code">
+<pre>
+Module* makeLLVMModule() {
+ // Module Construction
+ Module* mod = new Module("test");
+</pre>
+</div>
+
+<p>Exciting, isnât it!? All weâre doing here is instantiating a module and giving it a name. The name isnât particularly important unless youâre going to be dealing with multiple modules at once.</p>
+
+<div class="doc_code">
+<pre>
+ // Create a prototype for our function
+ std::vector<const Type*>argTypes;
+ argTypes.push_back(IntegerType::get(32));
+ argTypes.push_back(IntegerType::get(32));
+ argTypes.push_back(IntegerType::get(32));
+
+ FunctionType* functionSig = FunctionType::get(
+ /*return type*/ IntegerType::get(32),
+ /*arg types*/ argTypes,
+ /*varargs*/ false,
+ /*arg attrs*/ FuncTy_0_PAL);
+</pre>
+</div>
+
+<p>LLVM has a strong type system, including types for functions. So, before we can create our function, we need to create a <code>FunctionType</code> object to represent our functionâs type. There are four things that go into defining a <code>FunctionType</code>: the return type, the argumentsâ types, whether the function is varargs, and any attributes attached to the arguments. If you donât understand the latter two, donât worry. Theyâre not important for now.</p>
+
+<p>We construct our <code>FunctionType</code> by first creating a std::vector of Typeâs to hold to types of the arguments. In the case of our <code>mul_add</code> function, that means three 32-bit integers. Then, we pass in the return type (another 32-bit integer), our list of argument types, and the varargs and attributes, and weâve got ourselves a FunctionType.</p>
+
+<p>Now that we have a <code>FunctionType</code>, of course, it would be nice to use it for something...</p>
+
+<div class="doc_code">
+<pre>
+ Function* mul_add = new Function(
+ /*func type*/ functionSig,
+ /*linkage*/ GlobalValue::ExternalLinkage,
+ /*name*/ "mul_add",
+ /*module*/ mod);
+
+ mul_add->setCallingConv(CallingConv::C);
+</pre>
+</div>
+
+<p>Creating a function is as easy as calling its constructor and passing the appropriate parameters. The first parameter is the function type that we created earlier. The second is the functionâs linkage type. This one is important for optimization and linking, but for now weâll just play it safe and give it external linkage. If you donât know what to choose, external is probably your safest bet.</p>
+
+<p>The third and fourth parameters give the function a name and add it to our module, respectively. In addition, we set the calling convention for our new function to be the C calling convention. This isnât strictly necessary, but it insures that our new function will interoperate properly with C code, which is a good thing.</p>
+
+<div class="doc_code">
+<pre>
+ Function::arg_iterator args = mul_add->arg_begin();
+ Value* x = args++;
+ x->setName("x");
+ Value* y = args++;
+ y->setName("y");
+ Value* z = args++;
+ z->setName("z");
+</pre>
+</div>
+
+<p>While weâre setting up our function, letâs also give names to the parameters. This also isnât strictly necessary (LLVM will generate names for them if you donât specify them), but itâll make looking at our output somewhat more pleasant. To name the parameters, we iterator over the arguments of our function, and call <code>setName()</code> on them. Weâll also keep the pointer to <code>x</code>, <code>y</code>, and <code>z</code> around, since weâll need them when we get around to creating instructions.</p>
+
+<p>Great! We have a function now. But what good is a function if it has no body? Before we start working on a body for our new function, we need to recall some details of the LLVM IR. The IR, being an abstract assembly language, represents control flow using jumps (we call them branches), both conditional and unconditional. The straight-line sequences of code between branches are called basic blocks, or just blocks. To create a body for our function, we fill it with blocks!</p>
+
+<div class="doc_code">
+<pre>
+ BasicBlock* block = new BasicBlock("entry", mul_add);
+ LLVMBuilder builder(block);
+</pre>
+</div>
+
+<p>We create a new basic block, as you might expect, by calling its constructor. All we need to tell it is its name and the function to which it belongs. In addition, weâre creating an <code>LLVMBuilder</code> object, which is a convenience interface for creating instructions and appending them to the end of a block. Instructions can be created through their constructors as well, but some of their interfaces are quite complicated. Unless you need a lot of control, using <code>LLVMBuilder</code> will make your life simpler.</p>
+
+<div class="doc_code">
+<pre>
+ Value* tmp = builder.CreateBinOp(Instruction::Mul,
+ x, y, "tmp");
+ Value* tmp2 = builder.CreateBinOp(Instruction::Add,
+ tmp, z, "tmp2");
+
+ builder.CreateRet(tmp2);
+}
+</pre>
+</div>
+
+<p>The final step in creating our function is to create the instructions that make it up. Our <code>mul_add</code> function is composed of just three instructions: a multiply, an add, and a return. <code>LLVMBuilder</code> gives us a simple interface for constructing these instructions and appending them to the âentryâ block. Each of the calls to <code>LLVMBuilder</code> returns a <code>Value*</code> that represents the value yielded by the instruction. Youâll also notice that, above, <code>x</code>, <code>y</code>, and <code>z</code> are also <code>Value*</code>âs, so itâs clear that instructions operate on <code>Value*</code>âs.</p>
+
+<p>And thatâs it! Now you can compile and run your code, and get a wonder textual print out of the LLVM IR we saw at the beginning.</p>
+
+<p> ... SECTION ABOUT USING llvm-config TO GET THE NECESSARY COMPILER FLAGS TO COMPILE YOUR CODE ... </p>
+
+</div>
+
+</body>
+</html>
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Added: llvm/trunk/docs/tutorial/index.html
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/docs/tutorial/index.html?rev=43200&view=auto
==============================================================================
--- llvm/trunk/docs/tutorial/index.html (added)
+++ llvm/trunk/docs/tutorial/index.html Sat Oct 20 00:23:06 2007
@@ -0,0 +1,32 @@
+<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN"
+ "http://www.w3.org/TR/html4/strict.dtd">
+<html>
+<head>
+ <title>LLVM Tutorial: Table of Contents</title>
+ <meta http-equiv="Content-Type" content="text/html; charset=utf-8">
+ <meta name="author" content="Owen Anderson">
+ <meta name="description"
+ content="LLVM Tutorial: Table of Contents.">
+ <link rel="stylesheet" href="../llvm.css" type="text/css">
+</head>
+
+<body>
+
+<div class="doc_title"> LLVM Tutorial: Table of Contents </div>
+
+<ol>
+ <li><a href="Introduction.html">An Introduction to LLVM: Basic Concepts and Design</a></li>
+ <li>Basic Tutorials
+ <ol>
+ <li><a href="Tutorial1.html">Tutorial 1: A First Function</a></li>
+ <li><a href="Tutorial2.html">Tutorial 2: A More Complicated Function</a></li>
+ <li><a href="Tutorial3.html">Tutorial 3: Reading and Writing Bitcode</a></li>
+ <li><a href="Tutorial4.html">Tutorial 4: Running Optimizations</a></li>
+ <li><a href="Tutorial5.html">Tutorial 5: Invoking the JIT</a></li>
+ </ol>
+ </li>
+ <li><a href="Example.html">Example: Using LLVM to execute a simple language in JIT</a></li>
+</ol>
+
+</body>
+</html>
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