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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>
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				8	<meta name="author" content="Chris Lattner">
				9	<meta name="author" content="Erick Tryzelaar">
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				14
NAKAMURA Takumi	05d0265	2011-04-18 23:59:50 +0000	[diff] [blame]	15	<h1>Kaleidoscope: Code generation to LLVM IR</h1>
Erick Tryzelaar	37c076b	2008-03-30 09:57:12 +0000	[diff] [blame]	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	<!-- *********************************************************************** -->
NAKAMURA Takumi	05d0265	2011-04-18 23:59:50 +0000	[diff] [blame]	41	<h2><a name="intro">Chapter 3 Introduction</a></h2>
Erick Tryzelaar	37c076b	2008-03-30 09:57:12 +0000	[diff] [blame]	42	<!-- *********************************************************************** -->
				43
NAKAMURA Takumi	f5af6ad	2011-04-23 00:30:22 +0000	[diff] [blame^]	44	<div>
Erick Tryzelaar	37c076b	2008-03-30 09:57:12 +0000	[diff] [blame]	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	<!-- *********************************************************************** -->
NAKAMURA Takumi	05d0265	2011-04-18 23:59:50 +0000	[diff] [blame]	60	<h2><a name="basics">Code Generation Setup</a></h2>
Erick Tryzelaar	37c076b	2008-03-30 09:57:12 +0000	[diff] [blame]	61	<!-- *********************************************************************** -->
				62
NAKAMURA Takumi	f5af6ad	2011-04-23 00:30:22 +0000	[diff] [blame^]	63	<div>
Erick Tryzelaar	37c076b	2008-03-30 09:57:12 +0000	[diff] [blame]	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	<!-- *********************************************************************** -->
NAKAMURA Takumi	05d0265	2011-04-18 23:59:50 +0000	[diff] [blame]	131	<h2><a name="exprs">Expression Code Generation</a></h2>
Erick Tryzelaar	37c076b	2008-03-30 09:57:12 +0000	[diff] [blame]	132	<!-- *********************************************************************** -->
				133
NAKAMURA Takumi	f5af6ad	2011-04-23 00:30:22 +0000	[diff] [blame^]	134	<div>
Erick Tryzelaar	37c076b	2008-03-30 09:57:12 +0000	[diff] [blame]	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	<!-- *********************************************************************** -->
NAKAMURA Takumi	05d0265	2011-04-18 23:59:50 +0000	[diff] [blame]	266	<h2><a name="funcs">Function Code Generation</a></h2>
Erick Tryzelaar	37c076b	2008-03-30 09:57:12 +0000	[diff] [blame]	267	<!-- *********************************************************************** -->
				268
NAKAMURA Takumi	f5af6ad	2011-04-23 00:30:22 +0000	[diff] [blame^]	269	<div>
Erick Tryzelaar	37c076b	2008-03-30 09:57:12 +0000	[diff] [blame]	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	<!-- *********************************************************************** -->
NAKAMURA Takumi	05d0265	2011-04-18 23:59:50 +0000	[diff] [blame]	469	<h2><a name="driver">Driver Changes and Closing Thoughts</a></h2>
Erick Tryzelaar	37c076b	2008-03-30 09:57:12 +0000	[diff] [blame]	470	<!-- *********************************************************************** -->
				471
NAKAMURA Takumi	f5af6ad	2011-04-23 00:30:22 +0000	[diff] [blame^]	472	<div>
Erick Tryzelaar	37c076b	2008-03-30 09:57:12 +0000	[diff] [blame]	473
				474	<p>
				475	For now, code generation to LLVM doesn't really get us much, except that we can
				476	look at the pretty IR calls. The sample code inserts calls to Codegen into the
				477	"<tt>Toplevel.main_loop</tt>", and then dumps out the LLVM IR. This gives a
				478	nice way to look at the LLVM IR for simple functions. For example:
				479	</p>
				480
				481	<div class="doc_code">
				482	<pre>
				483	ready> <b>4+5</b>;
				484	Read top-level expression:
				485	define double @""() {
				486	entry:
Dan Gohman	a9445e1	2010-03-02 01:11:08 +0000	[diff] [blame]	487	%addtmp = fadd double 4.000000e+00, 5.000000e+00
Erick Tryzelaar	37c076b	2008-03-30 09:57:12 +0000	[diff] [blame]	488	ret double %addtmp
				489	}
				490	</pre>
				491	</div>
				492
				493	<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]	494	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]	495	support</a> in the next chapter. Also note that the code is very literally
				496	transcribed, no optimizations are being performed. We will
				497	<a href="OCamlLangImpl4.html#trivialconstfold">add optimizations</a> explicitly
				498	in the next chapter.</p>
				499
				500	<div class="doc_code">
				501	<pre>
				502	ready> <b>def foo(a b) aa + 2ab + bb;</b>
				503	Read function definition:
				504	define double @foo(double %a, double %b) {
				505	entry:
Dan Gohman	a9445e1	2010-03-02 01:11:08 +0000	[diff] [blame]	506	%multmp = fmul double %a, %a
				507	%multmp1 = fmul double 2.000000e+00, %a
				508	%multmp2 = fmul double %multmp1, %b
				509	%addtmp = fadd double %multmp, %multmp2
				510	%multmp3 = fmul double %b, %b
				511	%addtmp4 = fadd double %addtmp, %multmp3
Erick Tryzelaar	37c076b	2008-03-30 09:57:12 +0000	[diff] [blame]	512	ret double %addtmp4
				513	}
				514	</pre>
				515	</div>
				516
				517	<p>This shows some simple arithmetic. Notice the striking similarity to the
				518	LLVM builder calls that we use to create the instructions.</p>
				519
				520	<div class="doc_code">
				521	<pre>
				522	ready> <b>def bar(a) foo(a, 4.0) + bar(31337);</b>
				523	Read function definition:
				524	define double @bar(double %a) {
				525	entry:
Dan Gohman	3dfb3cf	2010-05-28 17:07:41 +0000	[diff] [blame]	526	%calltmp = call double @foo(double %a, double 4.000000e+00)
				527	%calltmp1 = call double @bar(double 3.133700e+04)
Dan Gohman	a9445e1	2010-03-02 01:11:08 +0000	[diff] [blame]	528	%addtmp = fadd double %calltmp, %calltmp1
Erick Tryzelaar	37c076b	2008-03-30 09:57:12 +0000	[diff] [blame]	529	ret double %addtmp
				530	}
				531	</pre>
				532	</div>
				533
				534	<p>This shows some function calls. Note that this function will take a long
				535	time to execute if you call it. In the future we'll add conditional control
				536	flow to actually make recursion useful :).</p>
				537
				538	<div class="doc_code">
				539	<pre>
				540	ready> <b>extern cos(x);</b>
				541	Read extern:
				542	declare double @cos(double)
				543
				544	ready> <b>cos(1.234);</b>
				545	Read top-level expression:
				546	define double @""() {
				547	entry:
Dan Gohman	3dfb3cf	2010-05-28 17:07:41 +0000	[diff] [blame]	548	%calltmp = call double @cos(double 1.234000e+00)
Erick Tryzelaar	37c076b	2008-03-30 09:57:12 +0000	[diff] [blame]	549	ret double %calltmp
				550	}
				551	</pre>
				552	</div>
				553
				554	<p>This shows an extern for the libm "cos" function, and a call to it.</p>
				555
				556
				557	<div class="doc_code">
				558	<pre>
				559	ready> <b>^D</b>
				560	; ModuleID = 'my cool jit'
				561
				562	define double @""() {
				563	entry:
Dan Gohman	a9445e1	2010-03-02 01:11:08 +0000	[diff] [blame]	564	%addtmp = fadd double 4.000000e+00, 5.000000e+00
Erick Tryzelaar	37c076b	2008-03-30 09:57:12 +0000	[diff] [blame]	565	ret double %addtmp
				566	}
				567
				568	define double @foo(double %a, double %b) {
				569	entry:
Dan Gohman	a9445e1	2010-03-02 01:11:08 +0000	[diff] [blame]	570	%multmp = fmul double %a, %a
				571	%multmp1 = fmul double 2.000000e+00, %a
				572	%multmp2 = fmul double %multmp1, %b
				573	%addtmp = fadd double %multmp, %multmp2
				574	%multmp3 = fmul double %b, %b
				575	%addtmp4 = fadd double %addtmp, %multmp3
Erick Tryzelaar	37c076b	2008-03-30 09:57:12 +0000	[diff] [blame]	576	ret double %addtmp4
				577	}
				578
				579	define double @bar(double %a) {
				580	entry:
Dan Gohman	3dfb3cf	2010-05-28 17:07:41 +0000	[diff] [blame]	581	%calltmp = call double @foo(double %a, double 4.000000e+00)
				582	%calltmp1 = call double @bar(double 3.133700e+04)
Dan Gohman	a9445e1	2010-03-02 01:11:08 +0000	[diff] [blame]	583	%addtmp = fadd double %calltmp, %calltmp1
Erick Tryzelaar	37c076b	2008-03-30 09:57:12 +0000	[diff] [blame]	584	ret double %addtmp
				585	}
				586
				587	declare double @cos(double)
				588
				589	define double @""() {
				590	entry:
Dan Gohman	3dfb3cf	2010-05-28 17:07:41 +0000	[diff] [blame]	591	%calltmp = call double @cos(double 1.234000e+00)
Erick Tryzelaar	37c076b	2008-03-30 09:57:12 +0000	[diff] [blame]	592	ret double %calltmp
				593	}
				594	</pre>
				595	</div>
				596
				597	<p>When you quit the current demo, it dumps out the IR for the entire module
				598	generated. Here you can see the big picture with all the functions referencing
				599	each other.</p>
				600
				601	<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]	602	describe how to <a href="OCamlLangImpl4.html">add JIT codegen and optimizer
Erick Tryzelaar	37c076b	2008-03-30 09:57:12 +0000	[diff] [blame]	603	support</a> to this so we can actually start running code!</p>
				604
				605	</div>
				606
				607
				608	<!-- *********************************************************************** -->
NAKAMURA Takumi	05d0265	2011-04-18 23:59:50 +0000	[diff] [blame]	609	<h2><a name="code">Full Code Listing</a></h2>
Erick Tryzelaar	37c076b	2008-03-30 09:57:12 +0000	[diff] [blame]	610	<!-- *********************************************************************** -->
				611
NAKAMURA Takumi	f5af6ad	2011-04-23 00:30:22 +0000	[diff] [blame^]	612	<div>
Erick Tryzelaar	37c076b	2008-03-30 09:57:12 +0000	[diff] [blame]	613
				614	<p>
				615	Here is the complete code listing for our running example, enhanced with the
				616	LLVM code generator. Because this uses the LLVM libraries, we need to link
				617	them in. To do this, we use the <a
				618	href="http://llvm.org/cmds/llvm-config.html">llvm-config</a> tool to inform
				619	our makefile/command line about which options to use:</p>
				620
				621	<div class="doc_code">
				622	<pre>
				623	# Compile
				624	ocamlbuild toy.byte
				625	# Run
				626	./toy.byte
				627	</pre>
				628	</div>
				629
				630	<p>Here is the code:</p>
				631
				632	<dl>
				633	<dt>_tags:</dt>
				634	<dd class="doc_code">
				635	<pre>
				636	<{lexer,parser}.ml>: use_camlp4, pp(camlp4of)
				637	<*.{byte,native}>: g++, use_llvm, use_llvm_analysis
				638	</pre>
				639	</dd>
				640
				641	<dt>myocamlbuild.ml:</dt>
				642	<dd class="doc_code">
				643	<pre>
				644	open Ocamlbuild_plugin;;
				645
				646	ocaml_lib ~extern:true "llvm";;
				647	ocaml_lib ~extern:true "llvm_analysis";;
				648
				649	flag ["link"; "ocaml"; "g++"] (S[A"-cc"; A"g++"]);;
				650	</pre>
				651	</dd>
				652
				653	<dt>token.ml:</dt>
				654	<dd class="doc_code">
				655	<pre>
				656	(*===----------------------------------------------------------------------===
				657	* Lexer Tokens
				658	===----------------------------------------------------------------------===)
				659
				660	(* The lexer returns these 'Kwd' if it is an unknown character, otherwise one of
				661	* these others for known things. *)
				662	type token =
				663	(* commands *)
				664	\| Def \| Extern
				665
				666	(* primary *)
				667	\| Ident of string \| Number of float
				668
				669	(* unknown *)
				670	\| Kwd of char
				671	</pre>
				672	</dd>
				673
				674	<dt>lexer.ml:</dt>
				675	<dd class="doc_code">
				676	<pre>
				677	(*===----------------------------------------------------------------------===
				678	* Lexer
				679	===----------------------------------------------------------------------===)
				680
				681	let rec lex = parser
				682	(* Skip any whitespace. *)
				683	\| [< ' (' ' \| '\n' \| '\r' \| '\t'); stream >] -> lex stream
				684
				685	(* identifier: [a-zA-Z][a-zA-Z0-9] *)
				686	\| [< ' ('A' .. 'Z' \| 'a' .. 'z' as c); stream >] ->
				687	let buffer = Buffer.create 1 in
				688	Buffer.add_char buffer c;
				689	lex_ident buffer stream
				690
				691	(* number: [0-9.]+ *)
				692	\| [< ' ('0' .. '9' as c); stream >] ->
				693	let buffer = Buffer.create 1 in
				694	Buffer.add_char buffer c;
				695	lex_number buffer stream
				696
				697	(* Comment until end of line. *)
				698	\| [< ' ('#'); stream >] ->
				699	lex_comment stream
				700
				701	(* Otherwise, just return the character as its ascii value. *)
				702	\| [< 'c; stream >] ->
				703	[< 'Token.Kwd c; lex stream >]
				704
				705	(* end of stream. *)
				706	\| [< >] -> [< >]
				707
				708	and lex_number buffer = parser
				709	\| [< ' ('0' .. '9' \| '.' as c); stream >] ->
				710	Buffer.add_char buffer c;
				711	lex_number buffer stream
				712	\| [< stream=lex >] ->
				713	[< 'Token.Number (float_of_string (Buffer.contents buffer)); stream >]
				714
				715	and lex_ident buffer = parser
				716	\| [< ' ('A' .. 'Z' \| 'a' .. 'z' \| '0' .. '9' as c); stream >] ->
				717	Buffer.add_char buffer c;
				718	lex_ident buffer stream
				719	\| [< stream=lex >] ->
				720	match Buffer.contents buffer with
				721	\| "def" -> [< 'Token.Def; stream >]
				722	\| "extern" -> [< 'Token.Extern; stream >]
				723	\| id -> [< 'Token.Ident id; stream >]
				724
				725	and lex_comment = parser
				726	\| [< ' ('\n'); stream=lex >] -> stream
				727	\| [< 'c; e=lex_comment >] -> e
				728	\| [< >] -> [< >]
				729	</pre>
				730	</dd>
				731
				732	<dt>ast.ml:</dt>
				733	<dd class="doc_code">
				734	<pre>
				735	(*===----------------------------------------------------------------------===
				736	* Abstract Syntax Tree (aka Parse Tree)
				737	===----------------------------------------------------------------------===)
				738
				739	(* expr - Base type for all expression nodes. *)
				740	type expr =
				741	(* variant for numeric literals like "1.0". *)
				742	\| Number of float
				743
				744	(* variant for referencing a variable, like "a". *)
				745	\| Variable of string
				746
				747	(* variant for a binary operator. *)
				748	\| Binary of char * expr * expr
				749
				750	(* variant for function calls. *)
				751	\| Call of string * expr array
				752
				753	(* proto - This type represents the "prototype" for a function, which captures
				754	* its name, and its argument names (thus implicitly the number of arguments the
				755	* function takes). *)
				756	type proto = Prototype of string * string array
				757
				758	(* func - This type represents a function definition itself. *)
				759	type func = Function of proto * expr
				760	</pre>
				761	</dd>
				762
				763	<dt>parser.ml:</dt>
				764	<dd class="doc_code">
				765	<pre>
				766	(*===---------------------------------------------------------------------===
				767	* Parser
				768	===---------------------------------------------------------------------===)
				769
				770	(* binop_precedence - This holds the precedence for each binary operator that is
				771	* defined *)
				772	let binop_precedence:(char, int) Hashtbl.t = Hashtbl.create 10
				773
				774	(* precedence - Get the precedence of the pending binary operator token. *)
				775	let precedence c = try Hashtbl.find binop_precedence c with Not_found -> -1
				776
				777	(* primary
				778	* ::= identifier
				779	* ::= numberexpr
				780	* ::= parenexpr *)
				781	let rec parse_primary = parser
				782	(* numberexpr ::= number *)
				783	\| [< 'Token.Number n >] -> Ast.Number n
				784
				785	(* parenexpr ::= '(' expression ')' *)
				786	\| [< 'Token.Kwd '('; e=parse_expr; 'Token.Kwd ')' ?? "expected ')'" >] -> e
				787
				788	(* identifierexpr
				789	* ::= identifier
				790	* ::= identifier '(' argumentexpr ')' *)
				791	\| [< 'Token.Ident id; stream >] ->
				792	let rec parse_args accumulator = parser
				793	\| [< e=parse_expr; stream >] ->
				794	begin parser
				795	\| [< 'Token.Kwd ','; e=parse_args (e :: accumulator) >] -> e
				796	\| [< >] -> e :: accumulator
				797	end stream
				798	\| [< >] -> accumulator
				799	in
				800	let rec parse_ident id = parser
				801	(* Call. *)
				802	\| [< 'Token.Kwd '(';
				803	args=parse_args [];
				804	'Token.Kwd ')' ?? "expected ')'">] ->
				805	Ast.Call (id, Array.of_list (List.rev args))
				806
				807	(* Simple variable ref. *)
				808	\| [< >] -> Ast.Variable id
				809	in
				810	parse_ident id stream
				811
				812	\| [< >] -> raise (Stream.Error "unknown token when expecting an expression.")
				813
				814	(* binoprhs
				815	* ::= ('+' primary)* *)
				816	and parse_bin_rhs expr_prec lhs stream =
				817	match Stream.peek stream with
				818	(* If this is a binop, find its precedence. *)
				819	\| Some (Token.Kwd c) when Hashtbl.mem binop_precedence c ->
				820	let token_prec = precedence c in
				821
				822	(* If this is a binop that binds at least as tightly as the current binop,
				823	* consume it, otherwise we are done. *)
				824	if token_prec < expr_prec then lhs else begin
				825	(* Eat the binop. *)
				826	Stream.junk stream;
				827
				828	(* Parse the primary expression after the binary operator. *)
				829	let rhs = parse_primary stream in
				830
				831	(* Okay, we know this is a binop. *)
				832	let rhs =
				833	match Stream.peek stream with
				834	\| Some (Token.Kwd c2) ->
				835	(* If BinOp binds less tightly with rhs than the operator after
				836	* rhs, let the pending operator take rhs as its lhs. *)
				837	let next_prec = precedence c2 in
				838	if token_prec < next_prec
				839	then parse_bin_rhs (token_prec + 1) rhs stream
				840	else rhs
				841	\| _ -> rhs
				842	in
				843
				844	(* Merge lhs/rhs. *)
				845	let lhs = Ast.Binary (c, lhs, rhs) in
				846	parse_bin_rhs expr_prec lhs stream
				847	end
				848	\| _ -> lhs
				849
				850	(* expression
				851	* ::= primary binoprhs *)
				852	and parse_expr = parser
				853	\| [< lhs=parse_primary; stream >] -> parse_bin_rhs 0 lhs stream
				854
				855	(* prototype
				856	* ::= id '(' id* ')' *)
				857	let parse_prototype =
				858	let rec parse_args accumulator = parser
				859	\| [< 'Token.Ident id; e=parse_args (id::accumulator) >] -> e
				860	\| [< >] -> accumulator
				861	in
				862
				863	parser
				864	\| [< 'Token.Ident id;
				865	'Token.Kwd '(' ?? "expected '(' in prototype";
				866	args=parse_args [];
				867	'Token.Kwd ')' ?? "expected ')' in prototype" >] ->
				868	(* success. *)
				869	Ast.Prototype (id, Array.of_list (List.rev args))
				870
				871	\| [< >] ->
				872	raise (Stream.Error "expected function name in prototype")
				873
				874	(* definition ::= 'def' prototype expression *)
				875	let parse_definition = parser
				876	\| [< 'Token.Def; p=parse_prototype; e=parse_expr >] ->
				877	Ast.Function (p, e)
				878
				879	(* toplevelexpr ::= expression *)
				880	let parse_toplevel = parser
				881	\| [< e=parse_expr >] ->
				882	(* Make an anonymous proto. *)
				883	Ast.Function (Ast.Prototype ("", [\|\|]), e)
				884
				885	(* external ::= 'extern' prototype *)
				886	let parse_extern = parser
				887	\| [< 'Token.Extern; e=parse_prototype >] -> e
				888	</pre>
				889	</dd>
				890
				891	<dt>codegen.ml:</dt>
				892	<dd class="doc_code">
				893	<pre>
				894	(*===----------------------------------------------------------------------===
				895	* Code Generation
				896	===----------------------------------------------------------------------===)
				897
				898	open Llvm
				899
				900	exception Error of string
				901
Erick Tryzelaar	1f3d276	2009-08-19 17:32:38 +0000	[diff] [blame]	902	let context = global_context ()
				903	let the_module = create_module context "my cool jit"
				904	let builder = builder context
Erick Tryzelaar	37c076b	2008-03-30 09:57:12 +0000	[diff] [blame]	905	let named_values:(string, llvalue) Hashtbl.t = Hashtbl.create 10
Erick Tryzelaar	9ef76b9	2010-03-08 19:32:18 +0000	[diff] [blame]	906	let double_type = double_type context
Erick Tryzelaar	37c076b	2008-03-30 09:57:12 +0000	[diff] [blame]	907
				908	let rec codegen_expr = function
				909	\| Ast.Number n -> const_float double_type n
				910	\| Ast.Variable name ->
				911	(try Hashtbl.find named_values name with
				912	\| Not_found -> raise (Error "unknown variable name"))
				913	\| Ast.Binary (op, lhs, rhs) ->
				914	let lhs_val = codegen_expr lhs in
				915	let rhs_val = codegen_expr rhs in
				916	begin
				917	match op with
				918	\| '+' -> build_add lhs_val rhs_val "addtmp" builder
				919	\| '-' -> build_sub lhs_val rhs_val "subtmp" builder
				920	\| '*' -> build_mul lhs_val rhs_val "multmp" builder
				921	\| '<' ->
				922	(* Convert bool 0/1 to double 0.0 or 1.0 *)
				923	let i = build_fcmp Fcmp.Ult lhs_val rhs_val "cmptmp" builder in
				924	build_uitofp i double_type "booltmp" builder
				925	\| _ -> raise (Error "invalid binary operator")
				926	end
				927	\| Ast.Call (callee, args) ->
				928	(* Look up the name in the module table. *)
				929	let callee =
				930	match lookup_function callee the_module with
				931	\| Some callee -> callee
				932	\| None -> raise (Error "unknown function referenced")
				933	in
				934	let params = params callee in
				935
				936	(* If argument mismatch error. *)
				937	if Array.length params == Array.length args then () else
				938	raise (Error "incorrect # arguments passed");
				939	let args = Array.map codegen_expr args in
				940	build_call callee args "calltmp" builder
				941
				942	let codegen_proto = function
				943	\| Ast.Prototype (name, args) ->
				944	(* Make the function type: double(double,double) etc. *)
				945	let doubles = Array.make (Array.length args) double_type in
				946	let ft = function_type double_type doubles in
				947	let f =
				948	match lookup_function name the_module with
				949	\| None -> declare_function name ft the_module
				950
				951	(* If 'f' conflicted, there was already something named 'name'. If it
				952	* has a body, don't allow redefinition or reextern. *)
				953	\| Some f ->
				954	(* If 'f' already has a body, reject this. *)
				955	if block_begin f <> At_end f then
				956	raise (Error "redefinition of function");
				957
				958	(* If 'f' took a different number of arguments, reject. *)
				959	if element_type (type_of f) <> ft then
				960	raise (Error "redefinition of function with different # args");
				961	f
				962	in
				963
				964	(* Set names for all arguments. *)
				965	Array.iteri (fun i a ->
				966	let n = args.(i) in
				967	set_value_name n a;
				968	Hashtbl.add named_values n a;
				969	) (params f);
				970	f
				971
				972	let codegen_func = function
				973	\| Ast.Function (proto, body) ->
				974	Hashtbl.clear named_values;
				975	let the_function = codegen_proto proto in
				976
				977	(* Create a new basic block to start insertion into. *)
Erick Tryzelaar	9ef76b9	2010-03-08 19:32:18 +0000	[diff] [blame]	978	let bb = append_block context "entry" the_function in
Erick Tryzelaar	37c076b	2008-03-30 09:57:12 +0000	[diff] [blame]	979	position_at_end bb builder;
				980
				981	try
				982	let ret_val = codegen_expr body in
				983
				984	(* Finish off the function. *)
				985	let _ = build_ret ret_val builder in
				986
				987	(* Validate the generated code, checking for consistency. *)
				988	Llvm_analysis.assert_valid_function the_function;
				989
				990	the_function
				991	with e ->
				992	delete_function the_function;
				993	raise e
				994	</pre>
				995	</dd>
				996
				997	<dt>toplevel.ml:</dt>
				998	<dd class="doc_code">
				999	<pre>
				1000	(*===----------------------------------------------------------------------===
				1001	* Top-Level parsing and JIT Driver
				1002	===----------------------------------------------------------------------===)
				1003
				1004	open Llvm
				1005
				1006	(* top ::= definition \| external \| expression \| ';' *)
				1007	let rec main_loop stream =
				1008	match Stream.peek stream with
				1009	\| None -> ()
				1010
				1011	(* ignore top-level semicolons. *)
				1012	\| Some (Token.Kwd ';') ->
				1013	Stream.junk stream;
				1014	main_loop stream
				1015
				1016	\| Some token ->
				1017	begin
				1018	try match token with
				1019	\| Token.Def ->
				1020	let e = Parser.parse_definition stream in
				1021	print_endline "parsed a function definition.";
				1022	dump_value (Codegen.codegen_func e);
				1023	\| Token.Extern ->
				1024	let e = Parser.parse_extern stream in
				1025	print_endline "parsed an extern.";
				1026	dump_value (Codegen.codegen_proto e);
				1027	\| _ ->
				1028	(* Evaluate a top-level expression into an anonymous function. *)
				1029	let e = Parser.parse_toplevel stream in
				1030	print_endline "parsed a top-level expr";
				1031	dump_value (Codegen.codegen_func e);
				1032	with Stream.Error s \| Codegen.Error s ->
				1033	(* Skip token for error recovery. *)
				1034	Stream.junk stream;
				1035	print_endline s;
				1036	end;
				1037	print_string "ready> "; flush stdout;
				1038	main_loop stream
				1039	</pre>
				1040	</dd>
				1041
				1042	<dt>toy.ml:</dt>
				1043	<dd class="doc_code">
				1044	<pre>
				1045	(*===----------------------------------------------------------------------===
				1046	* Main driver code.
				1047	===----------------------------------------------------------------------===)
				1048
				1049	open Llvm
				1050
				1051	let main () =
				1052	(* Install standard binary operators.
				1053	* 1 is the lowest precedence. *)
				1054	Hashtbl.add Parser.binop_precedence '<' 10;
				1055	Hashtbl.add Parser.binop_precedence '+' 20;
				1056	Hashtbl.add Parser.binop_precedence '-' 20;
				1057	Hashtbl.add Parser.binop_precedence '' 40; ( highest. *)
				1058
				1059	(* Prime the first token. *)
				1060	print_string "ready> "; flush stdout;
				1061	let stream = Lexer.lex (Stream.of_channel stdin) in
				1062
				1063	(* Run the main "interpreter loop" now. *)
				1064	Toplevel.main_loop stream;
				1065
				1066	(* Print out all the generated code. *)
				1067	dump_module Codegen.the_module
				1068	;;
				1069
				1070	main ()
				1071	</pre>
				1072	</dd>
				1073	</dl>
				1074
				1075	<a href="OCamlLangImpl4.html">Next: Adding JIT and Optimizer Support</a>
				1076	</div>
				1077
				1078	<!-- *********************************************************************** -->
				1079	<hr>
				1080	<address>
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				1085
				1086	<a href="mailto:sabre@nondot.org">Chris Lattner</a><br>
				1087	<a href="mailto:idadesub@users.sourceforge.net">Erick Tryzelaar</a><br>
NAKAMURA Takumi	b9a3363	2011-04-09 02:13:37 +0000	[diff] [blame]	1088	<a href="http://llvm.org/">The LLVM Compiler Infrastructure</a><br>
Dan Gohman	523e392	2010-02-03 17:27:31 +0000	[diff] [blame]	1089	Last modified: $Date$
Erick Tryzelaar	37c076b	2008-03-30 09:57:12 +0000	[diff] [blame]	1090	</address>
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