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Erick Tryzelaar	37c076b	2008-03-30 09:57:12 +0000	[diff] [blame]	1	<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN"
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				6	<title>Kaleidoscope: Implementing code generation to LLVM IR</title>
				7	<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
				8	<meta name="author" content="Chris Lattner">
				9	<meta name="author" content="Erick Tryzelaar">
				10	<link rel="stylesheet" href="../llvm.css" type="text/css">
				11	</head>
				12
				13	<body>
				14
				15	<div class="doc_title">Kaleidoscope: Code generation to LLVM IR</div>
				16
				17	<ul>
				18	<li><a href="index.html">Up to Tutorial Index</a></li>
				19	<li>Chapter 3
				20	<ol>
				21	<li><a href="#intro">Chapter 3 Introduction</a></li>
				22	<li><a href="#basics">Code Generation Setup</a></li>
				23	<li><a href="#exprs">Expression Code Generation</a></li>
				24	<li><a href="#funcs">Function Code Generation</a></li>
				25	<li><a href="#driver">Driver Changes and Closing Thoughts</a></li>
				26	<li><a href="#code">Full Code Listing</a></li>
				27	</ol>
				28	</li>
Chris Lattner	ff17b03	2008-12-12 04:20:01 +0000	[diff] [blame]	29	<li><a href="OCamlLangImpl4.html">Chapter 4</a>: Adding JIT and Optimizer
Erick Tryzelaar	37c076b	2008-03-30 09:57:12 +0000	[diff] [blame]	30	Support</li>
				31	</ul>
				32
				33	<div class="doc_author">
				34	<p>
				35	Written by <a href="mailto:sabre@nondot.org">Chris Lattner</a>
				36	and <a href="mailto:idadesub@users.sourceforge.net">Erick Tryzelaar</a>
				37	</p>
				38	</div>
				39
				40	<!-- *********************************************************************** -->
				41	<div class="doc_section"><a name="intro">Chapter 3 Introduction</a></div>
				42	<!-- *********************************************************************** -->
				43
				44	<div class="doc_text">
				45
				46	<p>Welcome to Chapter 3 of the "<a href="index.html">Implementing a language
				47	with LLVM</a>" tutorial. This chapter shows you how to transform the <a
				48	href="OCamlLangImpl2.html">Abstract Syntax Tree</a>, built in Chapter 2, into
				49	LLVM IR. This will teach you a little bit about how LLVM does things, as well
				50	as demonstrate how easy it is to use. It's much more work to build a lexer and
				51	parser than it is to generate LLVM IR code. :)
				52	</p>
				53
				54	<p><b>Please note</b>: the code in this chapter and later require LLVM 2.3 or
				55	LLVM SVN to work. LLVM 2.2 and before will not work with it.</p>
				56
				57	</div>
				58
				59	<!-- *********************************************************************** -->
				60	<div class="doc_section"><a name="basics">Code Generation Setup</a></div>
				61	<!-- *********************************************************************** -->
				62
				63	<div class="doc_text">
				64
				65	<p>
				66	In order to generate LLVM IR, we want some simple setup to get started. First
				67	we define virtual code generation (codegen) methods in each AST class:</p>
				68
				69	<div class="doc_code">
				70	<pre>
				71	let rec codegen_expr = function
				72	\| Ast.Number n -> ...
				73	\| Ast.Variable name -> ...
				74	</pre>
				75	</div>
				76
				77	<p>The <tt>Codegen.codegen_expr</tt> function says to emit IR for that AST node
				78	along with all the things it depends on, and they all return an LLVM Value
				79	object. "Value" is the class used to represent a "<a
				80	href="http://en.wikipedia.org/wiki/Static_single_assignment_form">Static Single
				81	Assignment (SSA)</a> register" or "SSA value" in LLVM. The most distinct aspect
				82	of SSA values is that their value is computed as the related instruction
				83	executes, and it does not get a new value until (and if) the instruction
				84	re-executes. In other words, there is no way to "change" an SSA value. For
				85	more information, please read up on <a
				86	href="http://en.wikipedia.org/wiki/Static_single_assignment_form">Static Single
				87	Assignment</a> - the concepts are really quite natural once you grok them.</p>
				88
				89	<p>The
				90	second thing we want is an "Error" exception like we used for the parser, which
				91	will be used to report errors found during code generation (for example, use of
				92	an undeclared parameter):</p>
				93
				94	<div class="doc_code">
				95	<pre>
				96	exception Error of string
				97
Erick Tryzelaar	1f3d276	2009-08-19 17:32:38 +0000	[diff] [blame]	98	let the_module = create_module (global_context ()) "my cool jit"
				99	let builder = builder (global_context ())
Erick Tryzelaar	37c076b	2008-03-30 09:57:12 +0000	[diff] [blame]	100	let named_values:(string, llvalue) Hashtbl.t = Hashtbl.create 10
Erick Tryzelaar	9ef76b9	2010-03-08 19:32:18 +0000	[diff] [blame]	101	let double_type = double_type context
Erick Tryzelaar	37c076b	2008-03-30 09:57:12 +0000	[diff] [blame]	102	</pre>
				103	</div>
				104
				105	<p>The static variables will be used during code generation.
				106	<tt>Codgen.the_module</tt> is the LLVM construct that contains all of the
				107	functions and global variables in a chunk of code. In many ways, it is the
				108	top-level structure that the LLVM IR uses to contain code.</p>
				109
				110	<p>The <tt>Codegen.builder</tt> object is a helper object that makes it easy to
				111	generate LLVM instructions. Instances of the <a
Duncan Sands	89f6d88	2008-04-13 06:22:09 +0000	[diff] [blame]	112	href="http://llvm.org/doxygen/IRBuilder_8h-source.html"><tt>IRBuilder</tt></a>
Erick Tryzelaar	37c076b	2008-03-30 09:57:12 +0000	[diff] [blame]	113	class keep track of the current place to insert instructions and has methods to
				114	create new instructions.</p>
				115
				116	<p>The <tt>Codegen.named_values</tt> map keeps track of which values are defined
				117	in the current scope and what their LLVM representation is. (In other words, it
				118	is a symbol table for the code). In this form of Kaleidoscope, the only things
				119	that can be referenced are function parameters. As such, function parameters
				120	will be in this map when generating code for their function body.</p>
				121
				122	<p>
				123	With these basics in place, we can start talking about how to generate code for
				124	each expression. Note that this assumes that the <tt>Codgen.builder</tt> has
				125	been set up to generate code <em>into</em> something. For now, we'll assume
				126	that this has already been done, and we'll just use it to emit code.</p>
				127
				128	</div>
				129
				130	<!-- *********************************************************************** -->
				131	<div class="doc_section"><a name="exprs">Expression Code Generation</a></div>
				132	<!-- *********************************************************************** -->
				133
				134	<div class="doc_text">
				135
				136	<p>Generating LLVM code for expression nodes is very straightforward: less
				137	than 30 lines of commented code for all four of our expression nodes. First
				138	we'll do numeric literals:</p>
				139
				140	<div class="doc_code">
				141	<pre>
				142	\| Ast.Number n -> const_float double_type n
				143	</pre>
				144	</div>
				145
				146	<p>In the LLVM IR, numeric constants are represented with the
				147	<tt>ConstantFP</tt> class, which holds the numeric value in an <tt>APFloat</tt>
				148	internally (<tt>APFloat</tt> has the capability of holding floating point
				149	constants of <em>A</em>rbitrary <em>P</em>recision). This code basically just
				150	creates and returns a <tt>ConstantFP</tt>. Note that in the LLVM IR
				151	that constants are all uniqued together and shared. For this reason, the API
Gabor Greif	97e378e	2008-05-21 18:30:15 +0000	[diff] [blame]	152	uses "the foo::get(..)" idiom instead of "new foo(..)" or "foo::Create(..)".</p>
Erick Tryzelaar	37c076b	2008-03-30 09:57:12 +0000	[diff] [blame]	153
				154	<div class="doc_code">
				155	<pre>
				156	\| Ast.Variable name ->
				157	(try Hashtbl.find named_values name with
				158	\| Not_found -> raise (Error "unknown variable name"))
				159	</pre>
				160	</div>
				161
				162	<p>References to variables are also quite simple using LLVM. In the simple
Benjamin Kramer	8040cd3	2009-10-12 14:46:08 +0000	[diff] [blame]	163	version of Kaleidoscope, we assume that the variable has already been emitted
Erick Tryzelaar	37c076b	2008-03-30 09:57:12 +0000	[diff] [blame]	164	somewhere and its value is available. In practice, the only values that can be
				165	in the <tt>Codegen.named_values</tt> map are function arguments. This code
				166	simply checks to see that the specified name is in the map (if not, an unknown
				167	variable is being referenced) and returns the value for it. In future chapters,
				168	we'll add support for <a href="LangImpl5.html#for">loop induction variables</a>
				169	in the symbol table, and for <a href="LangImpl7.html#localvars">local
				170	variables</a>.</p>
				171
				172	<div class="doc_code">
				173	<pre>
				174	\| Ast.Binary (op, lhs, rhs) ->
				175	let lhs_val = codegen_expr lhs in
				176	let rhs_val = codegen_expr rhs in
				177	begin
				178	match op with
				179	\| '+' -> build_add lhs_val rhs_val "addtmp" builder
				180	\| '-' -> build_sub lhs_val rhs_val "subtmp" builder
				181	\| '*' -> build_mul lhs_val rhs_val "multmp" builder
				182	\| '<' ->
				183	(* Convert bool 0/1 to double 0.0 or 1.0 *)
				184	let i = build_fcmp Fcmp.Ult lhs_val rhs_val "cmptmp" builder in
				185	build_uitofp i double_type "booltmp" builder
				186	\| _ -> raise (Error "invalid binary operator")
Erick Tryzelaar	35295ff	2008-03-31 08:44:50 +0000	[diff] [blame]	187	end
Erick Tryzelaar	37c076b	2008-03-30 09:57:12 +0000	[diff] [blame]	188	</pre>
				189	</div>
				190
				191	<p>Binary operators start to get more interesting. The basic idea here is that
				192	we recursively emit code for the left-hand side of the expression, then the
				193	right-hand side, then we compute the result of the binary expression. In this
				194	code, we do a simple switch on the opcode to create the right LLVM instruction.
				195	</p>
				196
				197	<p>In the example above, the LLVM builder class is starting to show its value.
Duncan Sands	89f6d88	2008-04-13 06:22:09 +0000	[diff] [blame]	198	IRBuilder knows where to insert the newly created instruction, all you have to
Erick Tryzelaar	37c076b	2008-03-30 09:57:12 +0000	[diff] [blame]	199	do is specify what instruction to create (e.g. with <tt>Llvm.create_add</tt>),
				200	which operands to use (<tt>lhs</tt> and <tt>rhs</tt> here) and optionally
				201	provide a name for the generated instruction.</p>
				202
				203	<p>One nice thing about LLVM is that the name is just a hint. For instance, if
				204	the code above emits multiple "addtmp" variables, LLVM will automatically
				205	provide each one with an increasing, unique numeric suffix. Local value names
				206	for instructions are purely optional, but it makes it much easier to read the
				207	IR dumps.</p>
				208
				209	<p><a href="../LangRef.html#instref">LLVM instructions</a> are constrained by
				210	strict rules: for example, the Left and Right operators of
				211	an <a href="../LangRef.html#i_add">add instruction</a> must have the same
				212	type, and the result type of the add must match the operand types. Because
				213	all values in Kaleidoscope are doubles, this makes for very simple code for add,
				214	sub and mul.</p>
				215
				216	<p>On the other hand, LLVM specifies that the <a
				217	href="../LangRef.html#i_fcmp">fcmp instruction</a> always returns an 'i1' value
				218	(a one bit integer). The problem with this is that Kaleidoscope wants the value to be a 0.0 or 1.0 value. In order to get these semantics, we combine the fcmp instruction with
				219	a <a href="../LangRef.html#i_uitofp">uitofp instruction</a>. This instruction
				220	converts its input integer into a floating point value by treating the input
				221	as an unsigned value. In contrast, if we used the <a
				222	href="../LangRef.html#i_sitofp">sitofp instruction</a>, the Kaleidoscope '<'
				223	operator would return 0.0 and -1.0, depending on the input value.</p>
				224
				225	<div class="doc_code">
				226	<pre>
				227	\| Ast.Call (callee, args) ->
				228	(* Look up the name in the module table. *)
				229	let callee =
				230	match lookup_function callee the_module with
				231	\| Some callee -> callee
				232	\| None -> raise (Error "unknown function referenced")
				233	in
				234	let params = params callee in
				235
				236	(* If argument mismatch error. *)
				237	if Array.length params == Array.length args then () else
				238	raise (Error "incorrect # arguments passed");
				239	let args = Array.map codegen_expr args in
				240	build_call callee args "calltmp" builder
				241	</pre>
				242	</div>
				243
				244	<p>Code generation for function calls is quite straightforward with LLVM. The
				245	code above initially does a function name lookup in the LLVM Module's symbol
				246	table. Recall that the LLVM Module is the container that holds all of the
				247	functions we are JIT'ing. By giving each function the same name as what the
				248	user specifies, we can use the LLVM symbol table to resolve function names for
				249	us.</p>
				250
				251	<p>Once we have the function to call, we recursively codegen each argument that
				252	is to be passed in, and create an LLVM <a href="../LangRef.html#i_call">call
				253	instruction</a>. Note that LLVM uses the native C calling conventions by
				254	default, allowing these calls to also call into standard library functions like
				255	"sin" and "cos", with no additional effort.</p>
				256
				257	<p>This wraps up our handling of the four basic expressions that we have so far
				258	in Kaleidoscope. Feel free to go in and add some more. For example, by
				259	browsing the <a href="../LangRef.html">LLVM language reference</a> you'll find
				260	several other interesting instructions that are really easy to plug into our
				261	basic framework.</p>
				262
				263	</div>
				264
				265	<!-- *********************************************************************** -->
				266	<div class="doc_section"><a name="funcs">Function Code Generation</a></div>
				267	<!-- *********************************************************************** -->
				268
				269	<div class="doc_text">
				270
				271	<p>Code generation for prototypes and functions must handle a number of
				272	details, which make their code less beautiful than expression code
				273	generation, but allows us to illustrate some important points. First, lets
				274	talk about code generation for prototypes: they are used both for function
				275	bodies and external function declarations. The code starts with:</p>
				276
				277	<div class="doc_code">
				278	<pre>
				279	let codegen_proto = function
				280	\| Ast.Prototype (name, args) ->
				281	(* Make the function type: double(double,double) etc. *)
				282	let doubles = Array.make (Array.length args) double_type in
				283	let ft = function_type double_type doubles in
Erick Tryzelaar	35295ff	2008-03-31 08:44:50 +0000	[diff] [blame]	284	let f =
Erick Tryzelaar	37c076b	2008-03-30 09:57:12 +0000	[diff] [blame]	285	match lookup_function name the_module with
				286	</pre>
				287	</div>
				288
				289	<p>This code packs a lot of power into a few lines. Note first that this
				290	function returns a "Function" instead of a "Value" (although at the moment
				291	they both are modeled by <tt>llvalue</tt> in ocaml). Because a "prototype"
				292	really talks about the external interface for a function (not the value computed
				293	by an expression), it makes sense for it to return the LLVM Function it
				294	corresponds to when codegen'd.</p>
				295
				296	<p>The call to <tt>Llvm.function_type</tt> creates the <tt>Llvm.llvalue</tt>
				297	that should be used for a given Prototype. Since all function arguments in
				298	Kaleidoscope are of type double, the first line creates a vector of "N" LLVM
				299	double types. It then uses the <tt>Llvm.function_type</tt> method to create a
				300	function type that takes "N" doubles as arguments, returns one double as a
				301	result, and that is not vararg (that uses the function
				302	<tt>Llvm.var_arg_function_type</tt>). Note that Types in LLVM are uniqued just
				303	like <tt>Constant</tt>s are, so you don't "new" a type, you "get" it.</p>
				304
				305	<p>The final line above checks if the function has already been defined in
				306	<tt>Codegen.the_module</tt>. If not, we will create it.</p>
				307
				308	<div class="doc_code">
				309	<pre>
				310	\| None -> declare_function name ft the_module
				311	</pre>
				312	</div>
				313
				314	<p>This indicates the type and name to use, as well as which module to insert
				315	into. By default we assume a function has
				316	<tt>Llvm.Linkage.ExternalLinkage</tt>. "<a href="LangRef.html#linkage">external
				317	linkage</a>" means that the function may be defined outside the current module
				318	and/or that it is callable by functions outside the module. The "<tt>name</tt>"
				319	passed in is the name the user specified: this name is registered in
				320	"<tt>Codegen.the_module</tt>"s symbol table, which is used by the function call
				321	code above.</p>
				322
				323	<p>In Kaleidoscope, I choose to allow redefinitions of functions in two cases:
				324	first, we want to allow 'extern'ing a function more than once, as long as the
				325	prototypes for the externs match (since all arguments have the same type, we
				326	just have to check that the number of arguments match). Second, we want to
Benjamin Kramer	8040cd3	2009-10-12 14:46:08 +0000	[diff] [blame]	327	allow 'extern'ing a function and then defining a body for it. This is useful
Erick Tryzelaar	37c076b	2008-03-30 09:57:12 +0000	[diff] [blame]	328	when defining mutually recursive functions.</p>
				329
				330	<div class="doc_code">
				331	<pre>
				332	(* If 'f' conflicted, there was already something named 'name'. If it
				333	* has a body, don't allow redefinition or reextern. *)
				334	\| Some f ->
				335	(* If 'f' already has a body, reject this. *)
				336	if Array.length (basic_blocks f) == 0 then () else
				337	raise (Error "redefinition of function");
				338
				339	(* If 'f' took a different number of arguments, reject. *)
				340	if Array.length (params f) == Array.length args then () else
				341	raise (Error "redefinition of function with different # args");
				342	f
				343	in
				344	</pre>
				345	</div>
				346
				347	<p>In order to verify the logic above, we first check to see if the pre-existing
				348	function is "empty". In this case, empty means that it has no basic blocks in
				349	it, which means it has no body. If it has no body, it is a forward
				350	declaration. Since we don't allow anything after a full definition of the
				351	function, the code rejects this case. If the previous reference to a function
				352	was an 'extern', we simply verify that the number of arguments for that
				353	definition and this one match up. If not, we emit an error.</p>
				354
				355	<div class="doc_code">
				356	<pre>
				357	(* Set names for all arguments. *)
				358	Array.iteri (fun i a ->
				359	let n = args.(i) in
				360	set_value_name n a;
				361	Hashtbl.add named_values n a;
				362	) (params f);
				363	f
				364	</pre>
				365	</div>
				366
				367	<p>The last bit of code for prototypes loops over all of the arguments in the
				368	function, setting the name of the LLVM Argument objects to match, and registering
				369	the arguments in the <tt>Codegen.named_values</tt> map for future use by the
				370	<tt>Ast.Variable</tt> variant. Once this is set up, it returns the Function
				371	object to the caller. Note that we don't check for conflicting
				372	argument names here (e.g. "extern foo(a b a)"). Doing so would be very
				373	straight-forward with the mechanics we have already used above.</p>
				374
				375	<div class="doc_code">
				376	<pre>
				377	let codegen_func = function
				378	\| Ast.Function (proto, body) ->
				379	Hashtbl.clear named_values;
				380	let the_function = codegen_proto proto in
				381	</pre>
				382	</div>
				383
				384	<p>Code generation for function definitions starts out simply enough: we just
				385	codegen the prototype (Proto) and verify that it is ok. We then clear out the
				386	<tt>Codegen.named_values</tt> map to make sure that there isn't anything in it
				387	from the last function we compiled. Code generation of the prototype ensures
				388	that there is an LLVM Function object that is ready to go for us.</p>
				389
				390	<div class="doc_code">
				391	<pre>
				392	(* Create a new basic block to start insertion into. *)
Erick Tryzelaar	9ef76b9	2010-03-08 19:32:18 +0000	[diff] [blame]	393	let bb = append_block context "entry" the_function in
Erick Tryzelaar	37c076b	2008-03-30 09:57:12 +0000	[diff] [blame]	394	position_at_end bb builder;
				395
				396	try
				397	let ret_val = codegen_expr body in
				398	</pre>
				399	</div>
				400
				401	<p>Now we get to the point where the <tt>Codegen.builder</tt> is set up. The
				402	first line creates a new
				403	<a href="http://en.wikipedia.org/wiki/Basic_block">basic block</a> (named
				404	"entry"), which is inserted into <tt>the_function</tt>. The second line then
				405	tells the builder that new instructions should be inserted into the end of the
				406	new basic block. Basic blocks in LLVM are an important part of functions that
				407	define the <a
				408	href="http://en.wikipedia.org/wiki/Control_flow_graph">Control Flow Graph</a>.
				409	Since we don't have any control flow, our functions will only contain one
				410	block at this point. We'll fix this in <a href="OCamlLangImpl5.html">Chapter
				411	5</a> :).</p>
				412
				413	<div class="doc_code">
				414	<pre>
				415	let ret_val = codegen_expr body in
				416
				417	(* Finish off the function. *)
				418	let _ = build_ret ret_val builder in
				419
				420	(* Validate the generated code, checking for consistency. *)
				421	Llvm_analysis.assert_valid_function the_function;
				422
				423	the_function
				424	</pre>
				425	</div>
				426
				427	<p>Once the insertion point is set up, we call the <tt>Codegen.codegen_func</tt>
				428	method for the root expression of the function. If no error happens, this emits
				429	code to compute the expression into the entry block and returns the value that
				430	was computed. Assuming no error, we then create an LLVM <a
				431	href="../LangRef.html#i_ret">ret instruction</a>, which completes the function.
				432	Once the function is built, we call
				433	<tt>Llvm_analysis.assert_valid_function</tt>, which is provided by LLVM. This
				434	function does a variety of consistency checks on the generated code, to
				435	determine if our compiler is doing everything right. Using this is important:
				436	it can catch a lot of bugs. Once the function is finished and validated, we
				437	return it.</p>
				438
				439	<div class="doc_code">
				440	<pre>
				441	with e ->
				442	delete_function the_function;
				443	raise e
				444	</pre>
				445	</div>
				446
				447	<p>The only piece left here is handling of the error case. For simplicity, we
				448	handle this by merely deleting the function we produced with the
				449	<tt>Llvm.delete_function</tt> method. This allows the user to redefine a
				450	function that they incorrectly typed in before: if we didn't delete it, it
				451	would live in the symbol table, with a body, preventing future redefinition.</p>
				452
				453	<p>This code does have a bug, though. Since the <tt>Codegen.codegen_proto</tt>
				454	can return a previously defined forward declaration, our code can actually delete
				455	a forward declaration. There are a number of ways to fix this bug, see what you
				456	can come up with! Here is a testcase:</p>
				457
				458	<div class="doc_code">
				459	<pre>
				460	extern foo(a b); # ok, defines foo.
				461	def foo(a b) c; # error, 'c' is invalid.
				462	def bar() foo(1, 2); # error, unknown function "foo"
				463	</pre>
				464	</div>
				465
				466	</div>
				467
				468	<!-- *********************************************************************** -->
				469	<div class="doc_section"><a name="driver">Driver Changes and
				470	Closing Thoughts</a></div>
				471	<!-- *********************************************************************** -->
				472
				473	<div class="doc_text">
				474
				475	<p>
				476	For now, code generation to LLVM doesn't really get us much, except that we can
				477	look at the pretty IR calls. The sample code inserts calls to Codegen into the
				478	"<tt>Toplevel.main_loop</tt>", and then dumps out the LLVM IR. This gives a
				479	nice way to look at the LLVM IR for simple functions. For example:
				480	</p>
				481
				482	<div class="doc_code">
				483	<pre>
				484	ready> <b>4+5</b>;
				485	Read top-level expression:
				486	define double @""() {
				487	entry:
Dan Gohman	a9445e1	2010-03-02 01:11:08 +0000	[diff] [blame]	488	%addtmp = fadd double 4.000000e+00, 5.000000e+00
Erick Tryzelaar	37c076b	2008-03-30 09:57:12 +0000	[diff] [blame]	489	ret double %addtmp
				490	}
				491	</pre>
				492	</div>
				493
				494	<p>Note how the parser turns the top-level expression into anonymous functions
Chris Lattner	ff17b03	2008-12-12 04:20:01 +0000	[diff] [blame]	495	for us. This will be handy when we add <a href="OCamlLangImpl4.html#jit">JIT
Erick Tryzelaar	37c076b	2008-03-30 09:57:12 +0000	[diff] [blame]	496	support</a> in the next chapter. Also note that the code is very literally
				497	transcribed, no optimizations are being performed. We will
				498	<a href="OCamlLangImpl4.html#trivialconstfold">add optimizations</a> explicitly
				499	in the next chapter.</p>
				500
				501	<div class="doc_code">
				502	<pre>
				503	ready> <b>def foo(a b) aa + 2ab + bb;</b>
				504	Read function definition:
				505	define double @foo(double %a, double %b) {
				506	entry:
Dan Gohman	a9445e1	2010-03-02 01:11:08 +0000	[diff] [blame]	507	%multmp = fmul double %a, %a
				508	%multmp1 = fmul double 2.000000e+00, %a
				509	%multmp2 = fmul double %multmp1, %b
				510	%addtmp = fadd double %multmp, %multmp2
				511	%multmp3 = fmul double %b, %b
				512	%addtmp4 = fadd double %addtmp, %multmp3
Erick Tryzelaar	37c076b	2008-03-30 09:57:12 +0000	[diff] [blame]	513	ret double %addtmp4
				514	}
				515	</pre>
				516	</div>
				517
				518	<p>This shows some simple arithmetic. Notice the striking similarity to the
				519	LLVM builder calls that we use to create the instructions.</p>
				520
				521	<div class="doc_code">
				522	<pre>
				523	ready> <b>def bar(a) foo(a, 4.0) + bar(31337);</b>
				524	Read function definition:
				525	define double @bar(double %a) {
				526	entry:
				527	%calltmp = call double @foo( double %a, double 4.000000e+00 )
				528	%calltmp1 = call double @bar( double 3.133700e+04 )
Dan Gohman	a9445e1	2010-03-02 01:11:08 +0000	[diff] [blame]	529	%addtmp = fadd double %calltmp, %calltmp1
Erick Tryzelaar	37c076b	2008-03-30 09:57:12 +0000	[diff] [blame]	530	ret double %addtmp
				531	}
				532	</pre>
				533	</div>
				534
				535	<p>This shows some function calls. Note that this function will take a long
				536	time to execute if you call it. In the future we'll add conditional control
				537	flow to actually make recursion useful :).</p>
				538
				539	<div class="doc_code">
				540	<pre>
				541	ready> <b>extern cos(x);</b>
				542	Read extern:
				543	declare double @cos(double)
				544
				545	ready> <b>cos(1.234);</b>
				546	Read top-level expression:
				547	define double @""() {
				548	entry:
				549	%calltmp = call double @cos( double 1.234000e+00 )
				550	ret double %calltmp
				551	}
				552	</pre>
				553	</div>
				554
				555	<p>This shows an extern for the libm "cos" function, and a call to it.</p>
				556
				557
				558	<div class="doc_code">
				559	<pre>
				560	ready> <b>^D</b>
				561	; ModuleID = 'my cool jit'
				562
				563	define double @""() {
				564	entry:
Dan Gohman	a9445e1	2010-03-02 01:11:08 +0000	[diff] [blame]	565	%addtmp = fadd double 4.000000e+00, 5.000000e+00
Erick Tryzelaar	37c076b	2008-03-30 09:57:12 +0000	[diff] [blame]	566	ret double %addtmp
				567	}
				568
				569	define double @foo(double %a, double %b) {
				570	entry:
Dan Gohman	a9445e1	2010-03-02 01:11:08 +0000	[diff] [blame]	571	%multmp = fmul double %a, %a
				572	%multmp1 = fmul double 2.000000e+00, %a
				573	%multmp2 = fmul double %multmp1, %b
				574	%addtmp = fadd double %multmp, %multmp2
				575	%multmp3 = fmul double %b, %b
				576	%addtmp4 = fadd double %addtmp, %multmp3
Erick Tryzelaar	37c076b	2008-03-30 09:57:12 +0000	[diff] [blame]	577	ret double %addtmp4
				578	}
				579
				580	define double @bar(double %a) {
				581	entry:
				582	%calltmp = call double @foo( double %a, double 4.000000e+00 )
				583	%calltmp1 = call double @bar( double 3.133700e+04 )
Dan Gohman	a9445e1	2010-03-02 01:11:08 +0000	[diff] [blame]	584	%addtmp = fadd double %calltmp, %calltmp1
Erick Tryzelaar	37c076b	2008-03-30 09:57:12 +0000	[diff] [blame]	585	ret double %addtmp
				586	}
				587
				588	declare double @cos(double)
				589
				590	define double @""() {
				591	entry:
				592	%calltmp = call double @cos( double 1.234000e+00 )
				593	ret double %calltmp
				594	}
				595	</pre>
				596	</div>
				597
				598	<p>When you quit the current demo, it dumps out the IR for the entire module
				599	generated. Here you can see the big picture with all the functions referencing
				600	each other.</p>
				601
				602	<p>This wraps up the third chapter of the Kaleidoscope tutorial. Up next, we'll
Chris Lattner	ff17b03	2008-12-12 04:20:01 +0000	[diff] [blame]	603	describe how to <a href="OCamlLangImpl4.html">add JIT codegen and optimizer
Erick Tryzelaar	37c076b	2008-03-30 09:57:12 +0000	[diff] [blame]	604	support</a> to this so we can actually start running code!</p>
				605
				606	</div>
				607
				608
				609	<!-- *********************************************************************** -->
				610	<div class="doc_section"><a name="code">Full Code Listing</a></div>
				611	<!-- *********************************************************************** -->
				612
				613	<div class="doc_text">
				614
				615	<p>
				616	Here is the complete code listing for our running example, enhanced with the
				617	LLVM code generator. Because this uses the LLVM libraries, we need to link
				618	them in. To do this, we use the <a
				619	href="http://llvm.org/cmds/llvm-config.html">llvm-config</a> tool to inform
				620	our makefile/command line about which options to use:</p>
				621
				622	<div class="doc_code">
				623	<pre>
				624	# Compile
				625	ocamlbuild toy.byte
				626	# Run
				627	./toy.byte
				628	</pre>
				629	</div>
				630
				631	<p>Here is the code:</p>
				632
				633	<dl>
				634	<dt>_tags:</dt>
				635	<dd class="doc_code">
				636	<pre>
				637	<{lexer,parser}.ml>: use_camlp4, pp(camlp4of)
				638	<*.{byte,native}>: g++, use_llvm, use_llvm_analysis
				639	</pre>
				640	</dd>
				641
				642	<dt>myocamlbuild.ml:</dt>
				643	<dd class="doc_code">
				644	<pre>
				645	open Ocamlbuild_plugin;;
				646
				647	ocaml_lib ~extern:true "llvm";;
				648	ocaml_lib ~extern:true "llvm_analysis";;
				649
				650	flag ["link"; "ocaml"; "g++"] (S[A"-cc"; A"g++"]);;
				651	</pre>
				652	</dd>
				653
				654	<dt>token.ml:</dt>
				655	<dd class="doc_code">
				656	<pre>
				657	(*===----------------------------------------------------------------------===
				658	* Lexer Tokens
				659	===----------------------------------------------------------------------===)
				660
				661	(* The lexer returns these 'Kwd' if it is an unknown character, otherwise one of
				662	* these others for known things. *)
				663	type token =
				664	(* commands *)
				665	\| Def \| Extern
				666
				667	(* primary *)
				668	\| Ident of string \| Number of float
				669
				670	(* unknown *)
				671	\| Kwd of char
				672	</pre>
				673	</dd>
				674
				675	<dt>lexer.ml:</dt>
				676	<dd class="doc_code">
				677	<pre>
				678	(*===----------------------------------------------------------------------===
				679	* Lexer
				680	===----------------------------------------------------------------------===)
				681
				682	let rec lex = parser
				683	(* Skip any whitespace. *)
				684	\| [< ' (' ' \| '\n' \| '\r' \| '\t'); stream >] -> lex stream
				685
				686	(* identifier: [a-zA-Z][a-zA-Z0-9] *)
				687	\| [< ' ('A' .. 'Z' \| 'a' .. 'z' as c); stream >] ->
				688	let buffer = Buffer.create 1 in
				689	Buffer.add_char buffer c;
				690	lex_ident buffer stream
				691
				692	(* number: [0-9.]+ *)
				693	\| [< ' ('0' .. '9' as c); stream >] ->
				694	let buffer = Buffer.create 1 in
				695	Buffer.add_char buffer c;
				696	lex_number buffer stream
				697
				698	(* Comment until end of line. *)
				699	\| [< ' ('#'); stream >] ->
				700	lex_comment stream
				701
				702	(* Otherwise, just return the character as its ascii value. *)
				703	\| [< 'c; stream >] ->
				704	[< 'Token.Kwd c; lex stream >]
				705
				706	(* end of stream. *)
				707	\| [< >] -> [< >]
				708
				709	and lex_number buffer = parser
				710	\| [< ' ('0' .. '9' \| '.' as c); stream >] ->
				711	Buffer.add_char buffer c;
				712	lex_number buffer stream
				713	\| [< stream=lex >] ->
				714	[< 'Token.Number (float_of_string (Buffer.contents buffer)); stream >]
				715
				716	and lex_ident buffer = parser
				717	\| [< ' ('A' .. 'Z' \| 'a' .. 'z' \| '0' .. '9' as c); stream >] ->
				718	Buffer.add_char buffer c;
				719	lex_ident buffer stream
				720	\| [< stream=lex >] ->
				721	match Buffer.contents buffer with
				722	\| "def" -> [< 'Token.Def; stream >]
				723	\| "extern" -> [< 'Token.Extern; stream >]
				724	\| id -> [< 'Token.Ident id; stream >]
				725
				726	and lex_comment = parser
				727	\| [< ' ('\n'); stream=lex >] -> stream
				728	\| [< 'c; e=lex_comment >] -> e
				729	\| [< >] -> [< >]
				730	</pre>
				731	</dd>
				732
				733	<dt>ast.ml:</dt>
				734	<dd class="doc_code">
				735	<pre>
				736	(*===----------------------------------------------------------------------===
				737	* Abstract Syntax Tree (aka Parse Tree)
				738	===----------------------------------------------------------------------===)
				739
				740	(* expr - Base type for all expression nodes. *)
				741	type expr =
				742	(* variant for numeric literals like "1.0". *)
				743	\| Number of float
				744
				745	(* variant for referencing a variable, like "a". *)
				746	\| Variable of string
				747
				748	(* variant for a binary operator. *)
				749	\| Binary of char * expr * expr
				750
				751	(* variant for function calls. *)
				752	\| Call of string * expr array
				753
				754	(* proto - This type represents the "prototype" for a function, which captures
				755	* its name, and its argument names (thus implicitly the number of arguments the
				756	* function takes). *)
				757	type proto = Prototype of string * string array
				758
				759	(* func - This type represents a function definition itself. *)
				760	type func = Function of proto * expr
				761	</pre>
				762	</dd>
				763
				764	<dt>parser.ml:</dt>
				765	<dd class="doc_code">
				766	<pre>
				767	(*===---------------------------------------------------------------------===
				768	* Parser
				769	===---------------------------------------------------------------------===)
				770
				771	(* binop_precedence - This holds the precedence for each binary operator that is
				772	* defined *)
				773	let binop_precedence:(char, int) Hashtbl.t = Hashtbl.create 10
				774
				775	(* precedence - Get the precedence of the pending binary operator token. *)
				776	let precedence c = try Hashtbl.find binop_precedence c with Not_found -> -1
				777
				778	(* primary
				779	* ::= identifier
				780	* ::= numberexpr
				781	* ::= parenexpr *)
				782	let rec parse_primary = parser
				783	(* numberexpr ::= number *)
				784	\| [< 'Token.Number n >] -> Ast.Number n
				785
				786	(* parenexpr ::= '(' expression ')' *)
				787	\| [< 'Token.Kwd '('; e=parse_expr; 'Token.Kwd ')' ?? "expected ')'" >] -> e
				788
				789	(* identifierexpr
				790	* ::= identifier
				791	* ::= identifier '(' argumentexpr ')' *)
				792	\| [< 'Token.Ident id; stream >] ->
				793	let rec parse_args accumulator = parser
				794	\| [< e=parse_expr; stream >] ->
				795	begin parser
				796	\| [< 'Token.Kwd ','; e=parse_args (e :: accumulator) >] -> e
				797	\| [< >] -> e :: accumulator
				798	end stream
				799	\| [< >] -> accumulator
				800	in
				801	let rec parse_ident id = parser
				802	(* Call. *)
				803	\| [< 'Token.Kwd '(';
				804	args=parse_args [];
				805	'Token.Kwd ')' ?? "expected ')'">] ->
				806	Ast.Call (id, Array.of_list (List.rev args))
				807
				808	(* Simple variable ref. *)
				809	\| [< >] -> Ast.Variable id
				810	in
				811	parse_ident id stream
				812
				813	\| [< >] -> raise (Stream.Error "unknown token when expecting an expression.")
				814
				815	(* binoprhs
				816	* ::= ('+' primary)* *)
				817	and parse_bin_rhs expr_prec lhs stream =
				818	match Stream.peek stream with
				819	(* If this is a binop, find its precedence. *)
				820	\| Some (Token.Kwd c) when Hashtbl.mem binop_precedence c ->
				821	let token_prec = precedence c in
				822
				823	(* If this is a binop that binds at least as tightly as the current binop,
				824	* consume it, otherwise we are done. *)
				825	if token_prec < expr_prec then lhs else begin
				826	(* Eat the binop. *)
				827	Stream.junk stream;
				828
				829	(* Parse the primary expression after the binary operator. *)
				830	let rhs = parse_primary stream in
				831
				832	(* Okay, we know this is a binop. *)
				833	let rhs =
				834	match Stream.peek stream with
				835	\| Some (Token.Kwd c2) ->
				836	(* If BinOp binds less tightly with rhs than the operator after
				837	* rhs, let the pending operator take rhs as its lhs. *)
				838	let next_prec = precedence c2 in
				839	if token_prec < next_prec
				840	then parse_bin_rhs (token_prec + 1) rhs stream
				841	else rhs
				842	\| _ -> rhs
				843	in
				844
				845	(* Merge lhs/rhs. *)
				846	let lhs = Ast.Binary (c, lhs, rhs) in
				847	parse_bin_rhs expr_prec lhs stream
				848	end
				849	\| _ -> lhs
				850
				851	(* expression
				852	* ::= primary binoprhs *)
				853	and parse_expr = parser
				854	\| [< lhs=parse_primary; stream >] -> parse_bin_rhs 0 lhs stream
				855
				856	(* prototype
				857	* ::= id '(' id* ')' *)
				858	let parse_prototype =
				859	let rec parse_args accumulator = parser
				860	\| [< 'Token.Ident id; e=parse_args (id::accumulator) >] -> e
				861	\| [< >] -> accumulator
				862	in
				863
				864	parser
				865	\| [< 'Token.Ident id;
				866	'Token.Kwd '(' ?? "expected '(' in prototype";
				867	args=parse_args [];
				868	'Token.Kwd ')' ?? "expected ')' in prototype" >] ->
				869	(* success. *)
				870	Ast.Prototype (id, Array.of_list (List.rev args))
				871
				872	\| [< >] ->
				873	raise (Stream.Error "expected function name in prototype")
				874
				875	(* definition ::= 'def' prototype expression *)
				876	let parse_definition = parser
				877	\| [< 'Token.Def; p=parse_prototype; e=parse_expr >] ->
				878	Ast.Function (p, e)
				879
				880	(* toplevelexpr ::= expression *)
				881	let parse_toplevel = parser
				882	\| [< e=parse_expr >] ->
				883	(* Make an anonymous proto. *)
				884	Ast.Function (Ast.Prototype ("", [\|\|]), e)
				885
				886	(* external ::= 'extern' prototype *)
				887	let parse_extern = parser
				888	\| [< 'Token.Extern; e=parse_prototype >] -> e
				889	</pre>
				890	</dd>
				891
				892	<dt>codegen.ml:</dt>
				893	<dd class="doc_code">
				894	<pre>
				895	(*===----------------------------------------------------------------------===
				896	* Code Generation
				897	===----------------------------------------------------------------------===)
				898
				899	open Llvm
				900
				901	exception Error of string
				902
Erick Tryzelaar	1f3d276	2009-08-19 17:32:38 +0000	[diff] [blame]	903	let context = global_context ()
				904	let the_module = create_module context "my cool jit"
				905	let builder = builder context
Erick Tryzelaar	37c076b	2008-03-30 09:57:12 +0000	[diff] [blame]	906	let named_values:(string, llvalue) Hashtbl.t = Hashtbl.create 10
Erick Tryzelaar	9ef76b9	2010-03-08 19:32:18 +0000	[diff] [blame]	907	let double_type = double_type context
Erick Tryzelaar	37c076b	2008-03-30 09:57:12 +0000	[diff] [blame]	908
				909	let rec codegen_expr = function
				910	\| Ast.Number n -> const_float double_type n
				911	\| Ast.Variable name ->
				912	(try Hashtbl.find named_values name with
				913	\| Not_found -> raise (Error "unknown variable name"))
				914	\| Ast.Binary (op, lhs, rhs) ->
				915	let lhs_val = codegen_expr lhs in
				916	let rhs_val = codegen_expr rhs in
				917	begin
				918	match op with
				919	\| '+' -> build_add lhs_val rhs_val "addtmp" builder
				920	\| '-' -> build_sub lhs_val rhs_val "subtmp" builder
				921	\| '*' -> build_mul lhs_val rhs_val "multmp" builder
				922	\| '<' ->
				923	(* Convert bool 0/1 to double 0.0 or 1.0 *)
				924	let i = build_fcmp Fcmp.Ult lhs_val rhs_val "cmptmp" builder in
				925	build_uitofp i double_type "booltmp" builder
				926	\| _ -> raise (Error "invalid binary operator")
				927	end
				928	\| Ast.Call (callee, args) ->
				929	(* Look up the name in the module table. *)
				930	let callee =
				931	match lookup_function callee the_module with
				932	\| Some callee -> callee
				933	\| None -> raise (Error "unknown function referenced")
				934	in
				935	let params = params callee in
				936
				937	(* If argument mismatch error. *)
				938	if Array.length params == Array.length args then () else
				939	raise (Error "incorrect # arguments passed");
				940	let args = Array.map codegen_expr args in
				941	build_call callee args "calltmp" builder
				942
				943	let codegen_proto = function
				944	\| Ast.Prototype (name, args) ->
				945	(* Make the function type: double(double,double) etc. *)
				946	let doubles = Array.make (Array.length args) double_type in
				947	let ft = function_type double_type doubles in
				948	let f =
				949	match lookup_function name the_module with
				950	\| None -> declare_function name ft the_module
				951
				952	(* If 'f' conflicted, there was already something named 'name'. If it
				953	* has a body, don't allow redefinition or reextern. *)
				954	\| Some f ->
				955	(* If 'f' already has a body, reject this. *)
				956	if block_begin f <> At_end f then
				957	raise (Error "redefinition of function");
				958
				959	(* If 'f' took a different number of arguments, reject. *)
				960	if element_type (type_of f) <> ft then
				961	raise (Error "redefinition of function with different # args");
				962	f
				963	in
				964
				965	(* Set names for all arguments. *)
				966	Array.iteri (fun i a ->
				967	let n = args.(i) in
				968	set_value_name n a;
				969	Hashtbl.add named_values n a;
				970	) (params f);
				971	f
				972
				973	let codegen_func = function
				974	\| Ast.Function (proto, body) ->
				975	Hashtbl.clear named_values;
				976	let the_function = codegen_proto proto in
				977
				978	(* Create a new basic block to start insertion into. *)
Erick Tryzelaar	9ef76b9	2010-03-08 19:32:18 +0000	[diff] [blame]	979	let bb = append_block context "entry" the_function in
Erick Tryzelaar	37c076b	2008-03-30 09:57:12 +0000	[diff] [blame]	980	position_at_end bb builder;
				981
				982	try
				983	let ret_val = codegen_expr body in
				984
				985	(* Finish off the function. *)
				986	let _ = build_ret ret_val builder in
				987
				988	(* Validate the generated code, checking for consistency. *)
				989	Llvm_analysis.assert_valid_function the_function;
				990
				991	the_function
				992	with e ->
				993	delete_function the_function;
				994	raise e
				995	</pre>
				996	</dd>
				997
				998	<dt>toplevel.ml:</dt>
				999	<dd class="doc_code">
				1000	<pre>
				1001	(*===----------------------------------------------------------------------===
				1002	* Top-Level parsing and JIT Driver
				1003	===----------------------------------------------------------------------===)
				1004
				1005	open Llvm
				1006
				1007	(* top ::= definition \| external \| expression \| ';' *)
				1008	let rec main_loop stream =
				1009	match Stream.peek stream with
				1010	\| None -> ()
				1011
				1012	(* ignore top-level semicolons. *)
				1013	\| Some (Token.Kwd ';') ->
				1014	Stream.junk stream;
				1015	main_loop stream
				1016
				1017	\| Some token ->
				1018	begin
				1019	try match token with
				1020	\| Token.Def ->
				1021	let e = Parser.parse_definition stream in
				1022	print_endline "parsed a function definition.";
				1023	dump_value (Codegen.codegen_func e);
				1024	\| Token.Extern ->
				1025	let e = Parser.parse_extern stream in
				1026	print_endline "parsed an extern.";
				1027	dump_value (Codegen.codegen_proto e);
				1028	\| _ ->
				1029	(* Evaluate a top-level expression into an anonymous function. *)
				1030	let e = Parser.parse_toplevel stream in
				1031	print_endline "parsed a top-level expr";
				1032	dump_value (Codegen.codegen_func e);
				1033	with Stream.Error s \| Codegen.Error s ->
				1034	(* Skip token for error recovery. *)
				1035	Stream.junk stream;
				1036	print_endline s;
				1037	end;
				1038	print_string "ready> "; flush stdout;
				1039	main_loop stream
				1040	</pre>
				1041	</dd>
				1042
				1043	<dt>toy.ml:</dt>
				1044	<dd class="doc_code">
				1045	<pre>
				1046	(*===----------------------------------------------------------------------===
				1047	* Main driver code.
				1048	===----------------------------------------------------------------------===)
				1049
				1050	open Llvm
				1051
				1052	let main () =
				1053	(* Install standard binary operators.
				1054	* 1 is the lowest precedence. *)
				1055	Hashtbl.add Parser.binop_precedence '<' 10;
				1056	Hashtbl.add Parser.binop_precedence '+' 20;
				1057	Hashtbl.add Parser.binop_precedence '-' 20;
				1058	Hashtbl.add Parser.binop_precedence '' 40; ( highest. *)
				1059
				1060	(* Prime the first token. *)
				1061	print_string "ready> "; flush stdout;
				1062	let stream = Lexer.lex (Stream.of_channel stdin) in
				1063
				1064	(* Run the main "interpreter loop" now. *)
				1065	Toplevel.main_loop stream;
				1066
				1067	(* Print out all the generated code. *)
				1068	dump_module Codegen.the_module
				1069	;;
				1070
				1071	main ()
				1072	</pre>
				1073	</dd>
				1074	</dl>
				1075
				1076	<a href="OCamlLangImpl4.html">Next: Adding JIT and Optimizer Support</a>
				1077	</div>
				1078
				1079	<!-- *********************************************************************** -->
				1080	<hr>
				1081	<address>
				1082	<a href="http://jigsaw.w3.org/css-validator/check/referer"><img
				1083	src="http://jigsaw.w3.org/css-validator/images/vcss" alt="Valid CSS!"></a>
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				1086
				1087	<a href="mailto:sabre@nondot.org">Chris Lattner</a><br>
				1088	<a href="mailto:idadesub@users.sourceforge.net">Erick Tryzelaar</a><br>
				1089	<a href="http://llvm.org">The LLVM Compiler Infrastructure</a><br>
Dan Gohman	523e392	2010-02-03 17:27:31 +0000	[diff] [blame]	1090	Last modified: $Date$
Erick Tryzelaar	37c076b	2008-03-30 09:57:12 +0000	[diff] [blame]	1091	</address>
				1092	</body>
				1093	</html>