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				4	<head>
Misha Brukman	3669299	2004-05-12 19:52:00 +0000	[diff] [blame]	5	<title>Stacker: An Example Of Using LLVM</title>
Brian Gaeke	9018148	2003-11-24 02:52:51 +0000	[diff] [blame]	6	<link rel="stylesheet" href="llvm.css" type="text/css">
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				12	<body>
Misha Brukman	3669299	2004-05-12 19:52:00 +0000	[diff] [blame]	13
Brian Gaeke	9018148	2003-11-24 02:52:51 +0000	[diff] [blame]	14	<div class="doc_title">Stacker: An Example Of Using LLVM</div>
Misha Brukman	3669299	2004-05-12 19:52:00 +0000	[diff] [blame]	15
Brian Gaeke	9018148	2003-11-24 02:52:51 +0000	[diff] [blame]	16	<ol>
				17	<li><a href="#abstract">Abstract</a></li>
				18	<li><a href="#introduction">Introduction</a></li>
Brian Gaeke	07e89e4	2003-11-24 17:03:38 +0000	[diff] [blame]	19	<li><a href="#lessons">Lessons I Learned About LLVM</a>
				20	<ol>
				21	<li><a href="#value">Everything's a Value!</a></li>
				22	<li><a href="#terminate">Terminate Those Blocks!</a></li>
				23	<li><a href="#blocks">Concrete Blocks</a></li>
				24	<li><a href="#push_back">push_back Is Your Friend</a></li>
				25	<li><a href="#gep">The Wily GetElementPtrInst</a></li>
				26	<li><a href="#linkage">Getting Linkage Types Right</a></li>
				27	<li><a href="#constants">Constants Are Easier Than That!</a></li>
Misha Brukman	3669299	2004-05-12 19:52:00 +0000	[diff] [blame]	28	</ol></li>
Brian Gaeke	9018148	2003-11-24 02:52:51 +0000	[diff] [blame]	29	<li><a href="#lexicon">The Stacker Lexicon</a>
				30	<ol>
Misha Brukman	3669299	2004-05-12 19:52:00 +0000	[diff] [blame]	31	<li><a href="#stack">The Stack</a></li>
				32	<li><a href="#punctuation">Punctuation</a></li>
				33	<li><a href="#comments">Comments</a></li>
				34	<li><a href="#literals">Literals</a></li>
				35	<li><a href="#words">Words</a></li>
				36	<li><a href="style">Standard Style</a></li>
				37	<li><a href="#builtins">Built-Ins</a></li>
				38	</ol></li>
Brian Gaeke	07e89e4	2003-11-24 17:03:38 +0000	[diff] [blame]	39	<li><a href="#example">Prime: A Complete Example</a></li>
				40	<li><a href="#internal">Internal Code Details</a>
				41	<ol>
				42	<li><a href="#directory">The Directory Structure </a></li>
				43	<li><a href="#lexer">The Lexer</a></li>
				44	<li><a href="#parser">The Parser</a></li>
				45	<li><a href="#compiler">The Compiler</a></li>
				46	<li><a href="#runtime">The Runtime</a></li>
				47	<li><a href="#driver">Compiler Driver</a></li>
				48	<li><a href="#tests">Test Programs</a></li>
Chris Lattner	e46d601	2003-11-25 01:35:06 +0000	[diff] [blame]	49	<li><a href="#exercise">Exercise</a></li>
				50	<li><a href="#todo">Things Remaining To Be Done</a></li>
Misha Brukman	3669299	2004-05-12 19:52:00 +0000	[diff] [blame]	51	</ol></li>
Brian Gaeke	9018148	2003-11-24 02:52:51 +0000	[diff] [blame]	52	</ol>
Misha Brukman	3669299	2004-05-12 19:52:00 +0000	[diff] [blame]	53
Chris Lattner	7911ce2	2004-05-23 21:07:27 +0000	[diff] [blame]	54	<div class="doc_author">
				55	<p>Written by <a href="mailto:rspencer@x10sys.com">Reid Spencer</a></p>
Brian Gaeke	9018148	2003-11-24 02:52:51 +0000	[diff] [blame]	56	</div>
Misha Brukman	3669299	2004-05-12 19:52:00 +0000	[diff] [blame]	57
Brian Gaeke	9018148	2003-11-24 02:52:51 +0000	[diff] [blame]	58	<!-- ======================================================================= -->
Misha Brukman	3669299	2004-05-12 19:52:00 +0000	[diff] [blame]	59	<div class="doc_section"><a name="abstract">Abstract</a></div>
Brian Gaeke	9018148	2003-11-24 02:52:51 +0000	[diff] [blame]	60	<div class="doc_text">
				61	<p>This document is another way to learn about LLVM. Unlike the
				62	<a href="LangRef.html">LLVM Reference Manual</a> or
Chris Lattner	45ab10c	2003-12-18 06:40:22 +0000	[diff] [blame]	63	<a href="ProgrammersManual.html">LLVM Programmer's Manual</a>, here we learn
Chris Lattner	e46d601	2003-11-25 01:35:06 +0000	[diff] [blame]	64	about LLVM through the experience of creating a simple programming language
				65	named Stacker. Stacker was invented specifically as a demonstration of
Brian Gaeke	9018148	2003-11-24 02:52:51 +0000	[diff] [blame]	66	LLVM. The emphasis in this document is not on describing the
John Criswell	d000e1d	2003-12-18 16:43:17 +0000	[diff] [blame]	67	intricacies of LLVM itself but on how to use it to build your own
Brian Gaeke	9018148	2003-11-24 02:52:51 +0000	[diff] [blame]	68	compiler system.</p>
				69	</div>
				70	<!-- ======================================================================= -->
				71	<div class="doc_section"> <a name="introduction">Introduction</a> </div>
				72	<div class="doc_text">
				73	<p>Amongst other things, LLVM is a platform for compiler writers.
				74	Because of its exceptionally clean and small IR (intermediate
				75	representation), compiler writing with LLVM is much easier than with
Chris Lattner	45ab10c	2003-12-18 06:40:22 +0000	[diff] [blame]	76	other system. As proof, I wrote the entire compiler (language definition,
				77	lexer, parser, code generator, etc.) in about <em>four days</em>!
				78	That's important to know because it shows how quickly you can get a new
				79	language running when using LLVM. Furthermore, this was the <em >first</em>
Brian Gaeke	9018148	2003-11-24 02:52:51 +0000	[diff] [blame]	80	language the author ever created using LLVM. The learning curve is
				81	included in that four days.</p>
				82	<p>The language described here, Stacker, is Forth-like. Programs
John Criswell	d000e1d	2003-12-18 16:43:17 +0000	[diff] [blame]	83	are simple collections of word definitions, and the only thing definitions
Brian Gaeke	9018148	2003-11-24 02:52:51 +0000	[diff] [blame]	84	can do is manipulate a stack or generate I/O. Stacker is not a "real"
John Criswell	d000e1d	2003-12-18 16:43:17 +0000	[diff] [blame]	85	programming language; it's very simple. Although it is computationally
Brian Gaeke	9018148	2003-11-24 02:52:51 +0000	[diff] [blame]	86	complete, you wouldn't use it for your next big project. However,
John Criswell	d000e1d	2003-12-18 16:43:17 +0000	[diff] [blame]	87	the fact that it is complete, it's simple, and it <em>doesn't</em> have
Brian Gaeke	9018148	2003-11-24 02:52:51 +0000	[diff] [blame]	88	a C-like syntax make it useful for demonstration purposes. It shows
Chris Lattner	e46d601	2003-11-25 01:35:06 +0000	[diff] [blame]	89	that LLVM could be applied to a wide variety of languages.</p>
Brian Gaeke	9018148	2003-11-24 02:52:51 +0000	[diff] [blame]	90	<p>The basic notions behind stacker is very simple. There's a stack of
				91	integers (or character pointers) that the program manipulates. Pretty
				92	much the only thing the program can do is manipulate the stack and do
				93	some limited I/O operations. The language provides you with several
				94	built-in words that manipulate the stack in interesting ways. To get
				95	your feet wet, here's how you write the traditional "Hello, World"
				96	program in Stacker:</p>
				97	<p><code>: hello_world "Hello, World!" >s DROP CR ;<br>
				98	: MAIN hello_world ;<br></code></p>
				99	<p>This has two "definitions" (Stacker manipulates words, not
				100	functions and words have definitions): <code>MAIN</code> and <code>
John Criswell	d000e1d	2003-12-18 16:43:17 +0000	[diff] [blame]	101	hello_world</code>. The <code>MAIN</code> definition is standard; it
Brian Gaeke	9018148	2003-11-24 02:52:51 +0000	[diff] [blame]	102	tells Stacker where to start. Here, <code>MAIN</code> is defined to
				103	simply invoke the word <code>hello_world</code>. The
				104	<code>hello_world</code> definition tells stacker to push the
John Criswell	d000e1d	2003-12-18 16:43:17 +0000	[diff] [blame]	105	<code>"Hello, World!"</code> string on to the stack, print it out
Brian Gaeke	9018148	2003-11-24 02:52:51 +0000	[diff] [blame]	106	(<code>>s</code>), pop it off the stack (<code>DROP</code>), and
				107	finally print a carriage return (<code>CR</code>). Although
				108	<code>hello_world</code> uses the stack, its net effect is null. Well
				109	written Stacker definitions have that characteristic. </p>
				110	<p>Exercise for the reader: how could you make this a one line program?</p>
				111	</div>
				112	<!-- ======================================================================= -->
Brian Gaeke	07e89e4	2003-11-24 17:03:38 +0000	[diff] [blame]	113	<div class="doc_section"><a name="lessons"></a>Lessons I Learned About LLVM</div>
Brian Gaeke	9018148	2003-11-24 02:52:51 +0000	[diff] [blame]	114	<div class="doc_text">
Chris Lattner	e46d601	2003-11-25 01:35:06 +0000	[diff] [blame]	115	<p>Stacker was written for two purposes: </p>
				116	<ol>
				117	<li>to get the author over the learning curve, and</li>
				118	<li>to provide a simple example of how to write a compiler using LLVM.</li>
				119	</ol>
				120	<p>During the development of Stacker, many lessons about LLVM were
Brian Gaeke	9018148	2003-11-24 02:52:51 +0000	[diff] [blame]	121	learned. Those lessons are described in the following subsections.<p>
				122	</div>
Brian Gaeke	07e89e4	2003-11-24 17:03:38 +0000	[diff] [blame]	123	<!-- ======================================================================= -->
				124	<div class="doc_subsection"><a name="value"></a>Everything's a Value!</div>
				125	<div class="doc_text">
Chris Lattner	e46d601	2003-11-25 01:35:06 +0000	[diff] [blame]	126	<p>Although I knew that LLVM uses a Single Static Assignment (SSA) format,
Brian Gaeke	07e89e4	2003-11-24 17:03:38 +0000	[diff] [blame]	127	it wasn't obvious to me how prevalent this idea was in LLVM until I really
Chris Lattner	e46d601	2003-11-25 01:35:06 +0000	[diff] [blame]	128	started using it. Reading the <a href="ProgrammersManual.html">
John Criswell	d000e1d	2003-12-18 16:43:17 +0000	[diff] [blame]	129	Programmer's Manual</a> and <a href="LangRef.html">Language Reference</a>,
Chris Lattner	e46d601	2003-11-25 01:35:06 +0000	[diff] [blame]	130	I noted that most of the important LLVM IR (Intermediate Representation) C++
Brian Gaeke	07e89e4	2003-11-24 17:03:38 +0000	[diff] [blame]	131	classes were derived from the Value class. The full power of that simple
				132	design only became fully understood once I started constructing executable
				133	expressions for Stacker.</p>
				134	<p>This really makes your programming go faster. Think about compiling code
Chris Lattner	e46d601	2003-11-25 01:35:06 +0000	[diff] [blame]	135	for the following C/C++ expression: <code>(a\|b)*((x+1)/(y+1))</code>. Assuming
				136	the values are on the stack in the order a, b, x, y, this could be
				137	expressed in stacker as: <code>1 + SWAP 1 + / ROT2 OR *</code>.
				138	You could write a function using LLVM that computes this expression like this: </p>
Brian Gaeke	07e89e4	2003-11-24 17:03:38 +0000	[diff] [blame]	139	<pre><code>
				140	Value*
Chris Lattner	45ab10c	2003-12-18 06:40:22 +0000	[diff] [blame]	141	expression(BasicBlock* bb, Value* a, Value* b, Value* x, Value* y )
Brian Gaeke	07e89e4	2003-11-24 17:03:38 +0000	[diff] [blame]	142	{
				143	Instruction* tail = bb->getTerminator();
				144	ConstantSInt* one = ConstantSInt::get( Type::IntTy, 1);
				145	BinaryOperator* or1 =
Chris Lattner	0b404c8	2003-11-25 01:44:27 +0000	[diff] [blame]	146	BinaryOperator::create( Instruction::Or, a, b, "", tail );
Brian Gaeke	07e89e4	2003-11-24 17:03:38 +0000	[diff] [blame]	147	BinaryOperator* add1 =
Chris Lattner	0b404c8	2003-11-25 01:44:27 +0000	[diff] [blame]	148	BinaryOperator::create( Instruction::Add, x, one, "", tail );
Brian Gaeke	07e89e4	2003-11-24 17:03:38 +0000	[diff] [blame]	149	BinaryOperator* add2 =
Chris Lattner	0b404c8	2003-11-25 01:44:27 +0000	[diff] [blame]	150	BinaryOperator::create( Instruction::Add, y, one, "", tail );
Brian Gaeke	07e89e4	2003-11-24 17:03:38 +0000	[diff] [blame]	151	BinaryOperator* div1 =
Chris Lattner	0b404c8	2003-11-25 01:44:27 +0000	[diff] [blame]	152	BinaryOperator::create( Instruction::Div, add1, add2, "", tail);
Brian Gaeke	07e89e4	2003-11-24 17:03:38 +0000	[diff] [blame]	153	BinaryOperator* mult1 =
Chris Lattner	0b404c8	2003-11-25 01:44:27 +0000	[diff] [blame]	154	BinaryOperator::create( Instruction::Mul, or1, div1, "", tail );
Brian Gaeke	07e89e4	2003-11-24 17:03:38 +0000	[diff] [blame]	155
				156	return mult1;
				157	}
				158	</code></pre>
Chris Lattner	45ab10c	2003-12-18 06:40:22 +0000	[diff] [blame]	159	<p>"Okay, big deal," you say? It is a big deal. Here's why. Note that I didn't
Brian Gaeke	07e89e4	2003-11-24 17:03:38 +0000	[diff] [blame]	160	have to tell this function which kinds of Values are being passed in. They could be
Chris Lattner	45ab10c	2003-12-18 06:40:22 +0000	[diff] [blame]	161	<code>Instruction</code>s, <code>Constant</code>s, <code>GlobalVariable</code>s, or
				162	any of the other subclasses of <code>Value</code> that LLVM supports.
				163	Furthermore, if you specify Values that are incorrect for this sequence of
Chris Lattner	e46d601	2003-11-25 01:35:06 +0000	[diff] [blame]	164	operations, LLVM will either notice right away (at compilation time) or the LLVM
Chris Lattner	45ab10c	2003-12-18 06:40:22 +0000	[diff] [blame]	165	Verifier will pick up the inconsistency when the compiler runs. In either case
				166	LLVM prevents you from making a type error that gets passed through to the
				167	generated program. This <em>really</em> helps you write a compiler that
				168	always generates correct code!<p>
Brian Gaeke	07e89e4	2003-11-24 17:03:38 +0000	[diff] [blame]	169	<p>The second point is that we don't have to worry about branching, registers,
				170	stack variables, saving partial results, etc. The instructions we create
				171	<em>are</em> the values we use. Note that all that was created in the above
				172	code is a Constant value and five operators. Each of the instructions <em>is</em>
Chris Lattner	e46d601	2003-11-25 01:35:06 +0000	[diff] [blame]	173	the resulting value of that instruction. This saves a lot of time.</p>
Brian Gaeke	07e89e4	2003-11-24 17:03:38 +0000	[diff] [blame]	174	<p>The lesson is this: <em>SSA form is very powerful: there is no difference
Chris Lattner	e46d601	2003-11-25 01:35:06 +0000	[diff] [blame]	175	between a value and the instruction that created it.</em> This is fully
Brian Gaeke	07e89e4	2003-11-24 17:03:38 +0000	[diff] [blame]	176	enforced by the LLVM IR. Use it to your best advantage.</p>
				177	</div>
				178	<!-- ======================================================================= -->
				179	<div class="doc_subsection"><a name="terminate"></a>Terminate Those Blocks!</div>
				180	<div class="doc_text">
				181	<p>I had to learn about terminating blocks the hard way: using the debugger
				182	to figure out what the LLVM verifier was trying to tell me and begging for
				183	help on the LLVMdev mailing list. I hope you avoid this experience.</p>
				184	<p>Emblazon this rule in your mind:</p>
				185	<ul>
				186	<li><em>All</em> <code>BasicBlock</code>s in your compiler <b>must</b> be
				187	terminated with a terminating instruction (branch, return, etc.).
				188	</li>
				189	</ul>
				190	<p>Terminating instructions are a semantic requirement of the LLVM IR. There
				191	is no facility for implicitly chaining together blocks placed into a function
				192	in the order they occur. Indeed, in the general case, blocks will not be
				193	added to the function in the order of execution because of the recursive
				194	way compilers are written.</p>
				195	<p>Furthermore, if you don't terminate your blocks, your compiler code will
				196	compile just fine. You won't find out about the problem until you're running
				197	the compiler and the module you just created fails on the LLVM Verifier.</p>
				198	</div>
				199	<!-- ======================================================================= -->
				200	<div class="doc_subsection"><a name="blocks"></a>Concrete Blocks</div>
				201	<div class="doc_text">
				202	<p>After a little initial fumbling around, I quickly caught on to how blocks
Chris Lattner	e46d601	2003-11-25 01:35:06 +0000	[diff] [blame]	203	should be constructed. In general, here's what I learned:
Brian Gaeke	07e89e4	2003-11-24 17:03:38 +0000	[diff] [blame]	204	<ol>
				205	<li><em>Create your blocks early.</em> While writing your compiler, you
				206	will encounter several situations where you know apriori that you will
John Criswell	d000e1d	2003-12-18 16:43:17 +0000	[diff] [blame]	207	need several blocks. For example, if-then-else, switch, while, and for
Brian Gaeke	07e89e4	2003-11-24 17:03:38 +0000	[diff] [blame]	208	statements in C/C++ all need multiple blocks for expression in LVVM.
				209	The rule is, create them early.</li>
				210	<li><em>Terminate your blocks early.</em> This just reduces the chances
				211	that you forget to terminate your blocks which is required (go
				212	<a href="#terminate">here</a> for more).
				213	<li><em>Use getTerminator() for instruction insertion.</em> I noticed early on
				214	that many of the constructors for the Instruction classes take an optional
				215	<code>insert_before</code> argument. At first, I thought this was a mistake
				216	because clearly the normal mode of inserting instructions would be one at
				217	a time <em>after</em> some other instruction, not <em>before</em>. However,
				218	if you hold on to your terminating instruction (or use the handy dandy
				219	<code>getTerminator()</code> method on a <code>BasicBlock</code>), it can
				220	always be used as the <code>insert_before</code> argument to your instruction
				221	constructors. This causes the instruction to automatically be inserted in
Chris Lattner	e46d601	2003-11-25 01:35:06 +0000	[diff] [blame]	222	the RightPlace™ place, just before the terminating instruction. The
Brian Gaeke	07e89e4	2003-11-24 17:03:38 +0000	[diff] [blame]	223	nice thing about this design is that you can pass blocks around and insert
Chris Lattner	e46d601	2003-11-25 01:35:06 +0000	[diff] [blame]	224	new instructions into them without ever knowing what instructions came
Brian Gaeke	07e89e4	2003-11-24 17:03:38 +0000	[diff] [blame]	225	before. This makes for some very clean compiler design.</li>
				226	</ol>
				227	<p>The foregoing is such an important principal, its worth making an idiom:</p>
Misha Brukman	3669299	2004-05-12 19:52:00 +0000	[diff] [blame]	228	<pre>
				229	BasicBlock* bb = new BasicBlock();
Brian Gaeke	07e89e4	2003-11-24 17:03:38 +0000	[diff] [blame]	230	bb->getInstList().push_back( new Branch( ... ) );
				231	new Instruction(..., bb->getTerminator() );
Misha Brukman	3669299	2004-05-12 19:52:00 +0000	[diff] [blame]	232	</pre>
Brian Gaeke	07e89e4	2003-11-24 17:03:38 +0000	[diff] [blame]	233	<p>To make this clear, consider the typical if-then-else statement
				234	(see StackerCompiler::handle_if() method). We can set this up
				235	in a single function using LLVM in the following way: </p>
				236	<pre>
				237	using namespace llvm;
				238	BasicBlock*
				239	MyCompiler::handle_if( BasicBlock* bb, SetCondInst* condition )
				240	{
				241	// Create the blocks to contain code in the structure of if/then/else
Chris Lattner	45ab10c	2003-12-18 06:40:22 +0000	[diff] [blame]	242	BasicBlock* then_bb = new BasicBlock();
				243	BasicBlock* else_bb = new BasicBlock();
				244	BasicBlock* exit_bb = new BasicBlock();
Brian Gaeke	07e89e4	2003-11-24 17:03:38 +0000	[diff] [blame]	245
				246	// Insert the branch instruction for the "if"
Chris Lattner	45ab10c	2003-12-18 06:40:22 +0000	[diff] [blame]	247	bb->getInstList().push_back( new BranchInst( then_bb, else_bb, condition ) );
Brian Gaeke	07e89e4	2003-11-24 17:03:38 +0000	[diff] [blame]	248
				249	// Set up the terminating instructions
Chris Lattner	45ab10c	2003-12-18 06:40:22 +0000	[diff] [blame]	250	then->getInstList().push_back( new BranchInst( exit_bb ) );
				251	else->getInstList().push_back( new BranchInst( exit_bb ) );
Brian Gaeke	07e89e4	2003-11-24 17:03:38 +0000	[diff] [blame]	252
				253	// Fill in the then part .. details excised for brevity
Chris Lattner	45ab10c	2003-12-18 06:40:22 +0000	[diff] [blame]	254	this->fill_in( then_bb );
Brian Gaeke	07e89e4	2003-11-24 17:03:38 +0000	[diff] [blame]	255
				256	// Fill in the else part .. details excised for brevity
Chris Lattner	45ab10c	2003-12-18 06:40:22 +0000	[diff] [blame]	257	this->fill_in( else_bb );
Brian Gaeke	07e89e4	2003-11-24 17:03:38 +0000	[diff] [blame]	258
				259	// Return a block to the caller that can be filled in with the code
				260	// that follows the if/then/else construct.
Chris Lattner	45ab10c	2003-12-18 06:40:22 +0000	[diff] [blame]	261	return exit_bb;
Brian Gaeke	07e89e4	2003-11-24 17:03:38 +0000	[diff] [blame]	262	}
				263	</pre>
				264	<p>Presumably in the foregoing, the calls to the "fill_in" method would add
				265	the instructions for the "then" and "else" parts. They would use the third part
				266	of the idiom almost exclusively (inserting new instructions before the
				267	terminator). Furthermore, they could even recurse back to <code>handle_if</code>
John Criswell	d000e1d	2003-12-18 16:43:17 +0000	[diff] [blame]	268	should they encounter another if/then/else statement, and it will just work.</p>
Brian Gaeke	07e89e4	2003-11-24 17:03:38 +0000	[diff] [blame]	269	<p>Note how cleanly this all works out. In particular, the push_back methods on
				270	the <code>BasicBlock</code>'s instruction list. These are lists of type
Chris Lattner	45ab10c	2003-12-18 06:40:22 +0000	[diff] [blame]	271	<code>Instruction</code> (which is also of type <code>Value</code>). To create
Brian Gaeke	07e89e4	2003-11-24 17:03:38 +0000	[diff] [blame]	272	the "if" branch we merely instantiate a <code>BranchInst</code> that takes as
Chris Lattner	45ab10c	2003-12-18 06:40:22 +0000	[diff] [blame]	273	arguments the blocks to branch to and the condition to branch on. The
				274	<code>BasicBlock</code> objects act like branch labels! This new
				275	<code>BranchInst</code> terminates the <code>BasicBlock</code> provided
				276	as an argument. To give the caller a way to keep inserting after calling
John Criswell	d000e1d	2003-12-18 16:43:17 +0000	[diff] [blame]	277	<code>handle_if</code>, we create an <code>exit_bb</code> block which is
				278	returned
Chris Lattner	45ab10c	2003-12-18 06:40:22 +0000	[diff] [blame]	279	to the caller. Note that the <code>exit_bb</code> block is used as the
				280	terminator for both the <code>then_bb</code> and the <code>else_bb</code>
				281	blocks. This guarantees that no matter what else <code>handle_if</code>
				282	or <code>fill_in</code> does, they end up at the <code>exit_bb</code> block.
Brian Gaeke	07e89e4	2003-11-24 17:03:38 +0000	[diff] [blame]	283	</p>
				284	</div>
				285	<!-- ======================================================================= -->
				286	<div class="doc_subsection"><a name="push_back"></a>push_back Is Your Friend</div>
				287	<div class="doc_text">
				288	<p>
				289	One of the first things I noticed is the frequent use of the "push_back"
				290	method on the various lists. This is so common that it is worth mentioning.
				291	The "push_back" inserts a value into an STL list, vector, array, etc. at the
				292	end. The method might have also been named "insert_tail" or "append".
John Criswell	d000e1d	2003-12-18 16:43:17 +0000	[diff] [blame]	293	Although I've used STL quite frequently, my use of push_back wasn't very
Brian Gaeke	07e89e4	2003-11-24 17:03:38 +0000	[diff] [blame]	294	high in other programs. In LLVM, you'll use it all the time.
				295	</p>
				296	</div>
				297	<!-- ======================================================================= -->
				298	<div class="doc_subsection"><a name="gep"></a>The Wily GetElementPtrInst</div>
				299	<div class="doc_text">
				300	<p>
				301	It took a little getting used to and several rounds of postings to the LLVM
John Criswell	d000e1d	2003-12-18 16:43:17 +0000	[diff] [blame]	302	mailing list to wrap my head around this instruction correctly. Even though I had
Brian Gaeke	07e89e4	2003-11-24 17:03:38 +0000	[diff] [blame]	303	read the Language Reference and Programmer's Manual a couple times each, I still
				304	missed a few <em>very</em> key points:
				305	</p>
				306	<ul>
Misha Brukman	3669299	2004-05-12 19:52:00 +0000	[diff] [blame]	307	<li>GetElementPtrInst gives you back a Value for the last thing indexed.</li>
				308	<li>All global variables in LLVM are <em>pointers</em>.</li>
				309	<li>Pointers must also be dereferenced with the GetElementPtrInst
				310	instruction.</li>
Brian Gaeke	07e89e4	2003-11-24 17:03:38 +0000	[diff] [blame]	311	</ul>
				312	<p>This means that when you look up an element in the global variable (assuming
John Criswell	d000e1d	2003-12-18 16:43:17 +0000	[diff] [blame]	313	it's a struct or array), you <em>must</em> deference the pointer first! For many
Brian Gaeke	07e89e4	2003-11-24 17:03:38 +0000	[diff] [blame]	314	things, this leads to the idiom:
				315	</p>
Misha Brukman	3669299	2004-05-12 19:52:00 +0000	[diff] [blame]	316	<pre>
				317	std::vector<Value*> index_vector;
Brian Gaeke	07e89e4	2003-11-24 17:03:38 +0000	[diff] [blame]	318	index_vector.push_back( ConstantSInt::get( Type::LongTy, 0 );
				319	// ... push other indices ...
				320	GetElementPtrInst* gep = new GetElementPtrInst( ptr, index_vector );
Misha Brukman	3669299	2004-05-12 19:52:00 +0000	[diff] [blame]	321	</pre>
Brian Gaeke	07e89e4	2003-11-24 17:03:38 +0000	[diff] [blame]	322	<p>For example, suppose we have a global variable whose type is [24 x int]. The
				323	variable itself represents a <em>pointer</em> to that array. To subscript the
				324	array, we need two indices, not just one. The first index (0) dereferences the
				325	pointer. The second index subscripts the array. If you're a "C" programmer, this
				326	will run against your grain because you'll naturally think of the global array
				327	variable and the address of its first element as the same. That tripped me up
				328	for a while until I realized that they really do differ .. by <em>type</em>.
Chris Lattner	45ab10c	2003-12-18 06:40:22 +0000	[diff] [blame]	329	Remember that LLVM is strongly typed. Everything has a type.
John Criswell	d000e1d	2003-12-18 16:43:17 +0000	[diff] [blame]	330	The "type" of the global variable is [24 x int]*. That is, it's
Brian Gaeke	07e89e4	2003-11-24 17:03:38 +0000	[diff] [blame]	331	a pointer to an array of 24 ints. When you dereference that global variable with
Chris Lattner	e46d601	2003-11-25 01:35:06 +0000	[diff] [blame]	332	a single (0) index, you now have a "[24 x int]" type. Although
Brian Gaeke	07e89e4	2003-11-24 17:03:38 +0000	[diff] [blame]	333	the pointer value of the dereferenced global and the address of the zero'th element
				334	in the array will be the same, they differ in their type. The zero'th element has
				335	type "int" while the pointer value has type "[24 x int]".</p>
John Criswell	d000e1d	2003-12-18 16:43:17 +0000	[diff] [blame]	336	<p>Get this one aspect of LLVM right in your head, and you'll save yourself
Brian Gaeke	07e89e4	2003-11-24 17:03:38 +0000	[diff] [blame]	337	a lot of compiler writing headaches down the road.</p>
				338	</div>
				339	<!-- ======================================================================= -->
Brian Gaeke	9018148	2003-11-24 02:52:51 +0000	[diff] [blame]	340	<div class="doc_subsection"><a name="linkage"></a>Getting Linkage Types Right</div>
Brian Gaeke	07e89e4	2003-11-24 17:03:38 +0000	[diff] [blame]	341	<div class="doc_text">
				342	<p>Linkage types in LLVM can be a little confusing, especially if your compiler
Chris Lattner	45ab10c	2003-12-18 06:40:22 +0000	[diff] [blame]	343	writing mind has affixed firm concepts to particular words like "weak",
Brian Gaeke	07e89e4	2003-11-24 17:03:38 +0000	[diff] [blame]	344	"external", "global", "linkonce", etc. LLVM does <em>not</em> use the precise
John Criswell	d000e1d	2003-12-18 16:43:17 +0000	[diff] [blame]	345	definitions of, say, ELF or GCC, even though they share common terms. To be fair,
Brian Gaeke	07e89e4	2003-11-24 17:03:38 +0000	[diff] [blame]	346	the concepts are related and similar but not precisely the same. This can lead
				347	you to think you know what a linkage type represents but in fact it is slightly
				348	different. I recommend you read the
				349	<a href="LangRef.html#linkage"> Language Reference on this topic</a> very
Chris Lattner	e46d601	2003-11-25 01:35:06 +0000	[diff] [blame]	350	carefully. Then, read it again.<p>
Brian Gaeke	07e89e4	2003-11-24 17:03:38 +0000	[diff] [blame]	351	<p>Here are some handy tips that I discovered along the way:</p>
				352	<ul>
Alkis Evlogimenos	0744b5f	2004-03-11 10:14:21 +0000	[diff] [blame]	353	<li><em>Uninitialized means external.</em> That is, the symbol is declared in the current
John Criswell	d000e1d	2003-12-18 16:43:17 +0000	[diff] [blame]	354	module and can be used by that module, but it is not defined by that module.</li>
Chris Lattner	45ab10c	2003-12-18 06:40:22 +0000	[diff] [blame]	355	<li><em>Setting an initializer changes a global' linkage type.</em> Setting an
				356	initializer changes a global's linkage type from whatever it was to a normal,
John Criswell	d000e1d	2003-12-18 16:43:17 +0000	[diff] [blame]	357	defined global (not external). You'll need to call the setLinkage() method to
Chris Lattner	45ab10c	2003-12-18 06:40:22 +0000	[diff] [blame]	358	reset it if you specify the initializer after the GlobalValue has been constructed.
				359	This is important for LinkOnce and Weak linkage types.</li>
				360	<li><em>Appending linkage can keep track of things.</em> Appending linkage can
				361	be used to keep track of compilation information at runtime. It could be used,
				362	for example, to build a full table of all the C++ virtual tables or hold the
				363	C++ RTTI data, or whatever. Appending linkage can only be applied to arrays.
				364	All arrays with the same name in each module are concatenated together at link
				365	time.</li>
Brian Gaeke	07e89e4	2003-11-24 17:03:38 +0000	[diff] [blame]	366	</ul>
				367	</div>
				368	<!-- ======================================================================= -->
				369	<div class="doc_subsection"><a name="constants"></a>Constants Are Easier Than That!</div>
				370	<div class="doc_text">
				371	<p>
				372	Constants in LLVM took a little getting used to until I discovered a few utility
				373	functions in the LLVM IR that make things easier. Here's what I learned: </p>
				374	<ul>
				375	<li>Constants are Values like anything else and can be operands of instructions</li>
John Criswell	d000e1d	2003-12-18 16:43:17 +0000	[diff] [blame]	376	<li>Integer constants, frequently needed, can be created using the static "get"
Brian Gaeke	07e89e4	2003-11-24 17:03:38 +0000	[diff] [blame]	377	methods of the ConstantInt, ConstantSInt, and ConstantUInt classes. The nice thing
				378	about these is that you can "get" any kind of integer quickly.</li>
				379	<li>There's a special method on Constant class which allows you to get the null
				380	constant for <em>any</em> type. This is really handy for initializing large
				381	arrays or structures, etc.</li>
				382	</ul>
				383	</div>
Brian Gaeke	9018148	2003-11-24 02:52:51 +0000	[diff] [blame]	384	<!-- ======================================================================= -->
				385	<div class="doc_section"> <a name="lexicon">The Stacker Lexicon</a></div>
Chris Lattner	e46d601	2003-11-25 01:35:06 +0000	[diff] [blame]	386	<div class="doc_text"><p>This section describes the Stacker language</p></div>
Brian Gaeke	9018148	2003-11-24 02:52:51 +0000	[diff] [blame]	387	<div class="doc_subsection"><a name="stack"></a>The Stack</div>
				388	<div class="doc_text">
				389	<p>Stacker definitions define what they do to the global stack. Before
				390	proceeding, a few words about the stack are in order. The stack is simply
				391	a global array of 32-bit integers or pointers. A global index keeps track
Chris Lattner	e46d601	2003-11-25 01:35:06 +0000	[diff] [blame]	392	of the location of the top of the stack. All of this is hidden from the
John Criswell	d000e1d	2003-12-18 16:43:17 +0000	[diff] [blame]	393	programmer, but it needs to be noted because it is the foundation of the
Brian Gaeke	9018148	2003-11-24 02:52:51 +0000	[diff] [blame]	394	conceptual programming model for Stacker. When you write a definition,
				395	you are, essentially, saying how you want that definition to manipulate
				396	the global stack.</p>
				397	<p>Manipulating the stack can be quite hazardous. There is no distinction
				398	given and no checking for the various types of values that can be placed
				399	on the stack. Automatic coercion between types is performed. In many
John Criswell	d000e1d	2003-12-18 16:43:17 +0000	[diff] [blame]	400	cases, this is useful. For example, a boolean value placed on the stack
Brian Gaeke	9018148	2003-11-24 02:52:51 +0000	[diff] [blame]	401	can be interpreted as an integer with good results. However, using a
				402	word that interprets that boolean value as a pointer to a string to
				403	print out will almost always yield a crash. Stacker simply leaves it
				404	to the programmer to get it right without any interference or hindering
Chris Lattner	e46d601	2003-11-25 01:35:06 +0000	[diff] [blame]	405	on interpretation of the stack values. You've been warned. :) </p>
Brian Gaeke	9018148	2003-11-24 02:52:51 +0000	[diff] [blame]	406	</div>
				407	<!-- ======================================================================= -->
				408	<div class="doc_subsection"> <a name="punctuation"></a>Punctuation</div>
				409	<div class="doc_text">
				410	<p>Punctuation in Stacker is very simple. The colon and semi-colon
				411	characters are used to introduce and terminate a definition
				412	(respectively). Except for <em>FORWARD</em> declarations, definitions
				413	are all you can specify in Stacker. Definitions are read left to right.
Chris Lattner	e46d601	2003-11-25 01:35:06 +0000	[diff] [blame]	414	Immediately after the colon comes the name of the word being defined.
				415	The remaining words in the definition specify what the word does. The definition
				416	is terminated by a semi-colon.</p>
				417	<p>So, your typical definition will have the form:</p>
				418	<pre><code>: name ... ;</code></pre>
				419	<p>The <code>name</code> is up to you but it must start with a letter and contain
John Criswell	d000e1d	2003-12-18 16:43:17 +0000	[diff] [blame]	420	only letters, numbers, and underscore. Names are case sensitive and must not be
Chris Lattner	e46d601	2003-11-25 01:35:06 +0000	[diff] [blame]	421	the same as the name of a built-in word. The <code>...</code> is replaced by
John Criswell	d000e1d	2003-12-18 16:43:17 +0000	[diff] [blame]	422	the stack manipulating words that you wish to define <code>name</code> as. <p>
Chris Lattner	e46d601	2003-11-25 01:35:06 +0000	[diff] [blame]	423	</div>
				424	<!-- ======================================================================= -->
				425	<div class="doc_subsection"><a name="comments"></a>Comments</div>
				426	<div class="doc_text">
				427	<p>Stacker supports two types of comments. A hash mark (#) starts a comment
				428	that extends to the end of the line. It is identical to the kind of comments
				429	commonly used in shell scripts. A pair of parentheses also surround a comment.
				430	In both cases, the content of the comment is ignored by the Stacker compiler. The
				431	following does nothing in Stacker.
				432	</p>
				433	<pre><code>
				434	# This is a comment to end of line
				435	( This is an enclosed comment )
				436	</code></pre>
Chris Lattner	45ab10c	2003-12-18 06:40:22 +0000	[diff] [blame]	437	<p>See the <a href="#example">example</a> program to see comments in use in
Chris Lattner	e46d601	2003-11-25 01:35:06 +0000	[diff] [blame]	438	a real program.</p>
Brian Gaeke	9018148	2003-11-24 02:52:51 +0000	[diff] [blame]	439	</div>
				440	<!-- ======================================================================= -->
				441	<div class="doc_subsection"><a name="literals"></a>Literals</div>
				442	<div class="doc_text">
John Criswell	d000e1d	2003-12-18 16:43:17 +0000	[diff] [blame]	443	<p>There are three kinds of literal values in Stacker: Integers, Strings,
Brian Gaeke	9018148	2003-11-24 02:52:51 +0000	[diff] [blame]	444	and Booleans. In each case, the stack operation is to simply push the
John Criswell	d000e1d	2003-12-18 16:43:17 +0000	[diff] [blame]	445	value on to the stack. So, for example:<br/>
Brian Gaeke	9018148	2003-11-24 02:52:51 +0000	[diff] [blame]	446	<code> 42 " is the answer." TRUE </code><br/>
John Criswell	d000e1d	2003-12-18 16:43:17 +0000	[diff] [blame]	447	will push three values on to the stack: the integer 42, the
				448	string " is the answer.", and the boolean TRUE.</p>
Brian Gaeke	9018148	2003-11-24 02:52:51 +0000	[diff] [blame]	449	</div>
				450	<!-- ======================================================================= -->
				451	<div class="doc_subsection"><a name="words"></a>Words</div>
				452	<div class="doc_text">
				453	<p>Each definition in Stacker is composed of a set of words. Words are
				454	read and executed in order from left to right. There is very little
				455	checking in Stacker to make sure you're doing the right thing with
				456	the stack. It is assumed that the programmer knows how the stack
				457	transformation he applies will affect the program.</p>
				458	<p>Words in a definition come in two flavors: built-in and programmer
				459	defined. Simply mentioning the name of a previously defined or declared
Chris Lattner	45ab10c	2003-12-18 06:40:22 +0000	[diff] [blame]	460	programmer-defined word causes that word's stack actions to be invoked. It
Brian Gaeke	9018148	2003-11-24 02:52:51 +0000	[diff] [blame]	461	is somewhat like a function call in other languages. The built-in
Chris Lattner	45ab10c	2003-12-18 06:40:22 +0000	[diff] [blame]	462	words have various effects, described <a href="#builtins">below</a>.</p>
Brian Gaeke	9018148	2003-11-24 02:52:51 +0000	[diff] [blame]	463	<p>Sometimes you need to call a word before it is defined. For this, you can
Chris Lattner	e46d601	2003-11-25 01:35:06 +0000	[diff] [blame]	464	use the <code>FORWARD</code> declaration. It looks like this:</p>
Brian Gaeke	9018148	2003-11-24 02:52:51 +0000	[diff] [blame]	465	<p><code>FORWARD name ;</code></p>
				466	<p>This simply states to Stacker that "name" is the name of a definition
				467	that is defined elsewhere. Generally it means the definition can be found
				468	"forward" in the file. But, it doesn't have to be in the current compilation
				469	unit. Anything declared with <code>FORWARD</code> is an external symbol for
				470	linking.</p>
				471	</div>
				472	<!-- ======================================================================= -->
				473	<div class="doc_subsection"><a name="builtins"></a>Built In Words</div>
				474	<div class="doc_text">
				475	<p>The built-in words of the Stacker language are put in several groups
				476	depending on what they do. The groups are as follows:</p>
				477	<ol>
John Criswell	d000e1d	2003-12-18 16:43:17 +0000	[diff] [blame]	478	<li><em>Logical</em>: These words provide the logical operations for
Brian Gaeke	9018148	2003-11-24 02:52:51 +0000	[diff] [blame]	479	comparing stack operands.<br/>The words are: < > <= >=
				480	= <> true false.</li>
John Criswell	d000e1d	2003-12-18 16:43:17 +0000	[diff] [blame]	481	<li><em>Bitwise</em>: These words perform bitwise computations on
Brian Gaeke	9018148	2003-11-24 02:52:51 +0000	[diff] [blame]	482	their operands. <br/> The words are: << >> XOR AND NOT</li>
John Criswell	d000e1d	2003-12-18 16:43:17 +0000	[diff] [blame]	483	<li><em>Arithmetic</em>: These words perform arithmetic computations on
Brian Gaeke	9018148	2003-11-24 02:52:51 +0000	[diff] [blame]	484	their operands. <br/> The words are: ABS NEG + - * / MOD */ ++ -- MIN MAX</li>
				485	<li><em>Stack</em>These words manipulate the stack directly by moving
Chris Lattner	45ab10c	2003-12-18 06:40:22 +0000	[diff] [blame]	486	its elements around.<br/> The words are: DROP DROP2 NIP NIP2 DUP DUP2
				487	SWAP SWAP2 OVER OVER2 ROT ROT2 RROT RROT2 TUCK TUCK2 PICK SELECT ROLL</li>
John Criswell	d000e1d	2003-12-18 16:43:17 +0000	[diff] [blame]	488	<li><em>Memory</em>These words allocate, free, and manipulate memory
Brian Gaeke	9018148	2003-11-24 02:52:51 +0000	[diff] [blame]	489	areas outside the stack.<br/>The words are: MALLOC FREE GET PUT</li>
John Criswell	d000e1d	2003-12-18 16:43:17 +0000	[diff] [blame]	490	<li><em>Control</em>: These words alter the normal left to right flow
Brian Gaeke	9018148	2003-11-24 02:52:51 +0000	[diff] [blame]	491	of execution.<br/>The words are: IF ELSE ENDIF WHILE END RETURN EXIT RECURSE</li>
John Criswell	d000e1d	2003-12-18 16:43:17 +0000	[diff] [blame]	492	<li><em>I/O</em>: These words perform output on the standard output
Brian Gaeke	9018148	2003-11-24 02:52:51 +0000	[diff] [blame]	493	and input on the standard input. No other I/O is possible in Stacker.
				494	<br/>The words are: SPACE TAB CR >s >d >c <s <d <c.</li>
				495	</ol>
				496	<p>While you may be familiar with many of these operations from other
				497	programming languages, a careful review of their semantics is important
				498	for correct programming in Stacker. Of most importance is the effect
				499	that each of these built-in words has on the global stack. The effect is
				500	not always intuitive. To better describe the effects, we'll borrow from Forth the idiom of
				501	describing the effect on the stack with:</p>
				502	<p><code> BEFORE -- AFTER </code></p>
				503	<p>That is, to the left of the -- is a representation of the stack before
				504	the operation. To the right of the -- is a representation of the stack
				505	after the operation. In the table below that describes the operation of
				506	each of the built in words, we will denote the elements of the stack
				507	using the following construction:</p>
				508	<ol>
				509	<li><em>b</em> - a boolean truth value</li>
				510	<li><em>w</em> - a normal integer valued word.</li>
				511	<li><em>s</em> - a pointer to a string value</li>
Chris Lattner	e46d601	2003-11-25 01:35:06 +0000	[diff] [blame]	512	<li><em>p</em> - a pointer to a malloc'd memory block</li>
Brian Gaeke	9018148	2003-11-24 02:52:51 +0000	[diff] [blame]	513	</ol>
				514	</div>
Chris Lattner	45ab10c	2003-12-18 06:40:22 +0000	[diff] [blame]	515	<div class="doc_text" >
Misha Brukman	f39d5d6	2004-05-13 00:24:43 +0000	[diff] [blame]	516	<table class="doc_table">
				517	<tr class="doc_table"><td colspan="4">Definition Of Operation Of Built In Words</td></tr>
				518	<tr class="doc_table"><td colspan="4"><b>LOGICAL OPERATIONS</b></td></tr>
Chris Lattner	45ab10c	2003-12-18 06:40:22 +0000	[diff] [blame]	519	<tr class="doc_table">
Misha Brukman	f39d5d6	2004-05-13 00:24:43 +0000	[diff] [blame]	520	<td>Word</td>
				521	<td>Name</td>
				522	<td>Operation</td>
				523	<td>Description</td>
Chris Lattner	45ab10c	2003-12-18 06:40:22 +0000	[diff] [blame]	524	</tr>
Misha Brukman	f39d5d6	2004-05-13 00:24:43 +0000	[diff] [blame]	525	<tr class="doc_table">
				526	<td><</td>
				527	<td>LT</td>
				528	<td>w1 w2 -- b</td>
				529	<td>Two values (w1 and w2) are popped off the stack and
Brian Gaeke	9018148	2003-11-24 02:52:51 +0000	[diff] [blame]	530	compared. If w1 is less than w2, TRUE is pushed back on
				531	the stack, otherwise FALSE is pushed back on the stack.</td>
				532	</tr>
Misha Brukman	f39d5d6	2004-05-13 00:24:43 +0000	[diff] [blame]	533	<tr><td>></td>
				534	<td>GT</td>
				535	<td>w1 w2 -- b</td>
				536	<td>Two values (w1 and w2) are popped off the stack and
Brian Gaeke	9018148	2003-11-24 02:52:51 +0000	[diff] [blame]	537	compared. If w1 is greater than w2, TRUE is pushed back on
				538	the stack, otherwise FALSE is pushed back on the stack.</td>
				539	</tr>
Misha Brukman	f39d5d6	2004-05-13 00:24:43 +0000	[diff] [blame]	540	<tr><td>>=</td>
				541	<td>GE</td>
				542	<td>w1 w2 -- b</td>
				543	<td>Two values (w1 and w2) are popped off the stack and
Brian Gaeke	9018148	2003-11-24 02:52:51 +0000	[diff] [blame]	544	compared. If w1 is greater than or equal to w2, TRUE is
				545	pushed back on the stack, otherwise FALSE is pushed back
				546	on the stack.</td>
				547	</tr>
Misha Brukman	f39d5d6	2004-05-13 00:24:43 +0000	[diff] [blame]	548	<tr><td><=</td>
				549	<td>LE</td>
				550	<td>w1 w2 -- b</td>
				551	<td>Two values (w1 and w2) are popped off the stack and
Brian Gaeke	9018148	2003-11-24 02:52:51 +0000	[diff] [blame]	552	compared. If w1 is less than or equal to w2, TRUE is
				553	pushed back on the stack, otherwise FALSE is pushed back
				554	on the stack.</td>
				555	</tr>
Misha Brukman	f39d5d6	2004-05-13 00:24:43 +0000	[diff] [blame]	556	<tr><td>=</td>
				557	<td>EQ</td>
				558	<td>w1 w2 -- b</td>
				559	<td>Two values (w1 and w2) are popped off the stack and
Brian Gaeke	9018148	2003-11-24 02:52:51 +0000	[diff] [blame]	560	compared. If w1 is equal to w2, TRUE is
				561	pushed back on the stack, otherwise FALSE is pushed back
				562	</td>
				563	</tr>
Misha Brukman	f39d5d6	2004-05-13 00:24:43 +0000	[diff] [blame]	564	<tr><td><></td>
				565	<td>NE</td>
				566	<td>w1 w2 -- b</td>
				567	<td>Two values (w1 and w2) are popped off the stack and
Brian Gaeke	9018148	2003-11-24 02:52:51 +0000	[diff] [blame]	568	compared. If w1 is equal to w2, TRUE is
				569	pushed back on the stack, otherwise FALSE is pushed back
				570	</td>
				571	</tr>
Misha Brukman	f39d5d6	2004-05-13 00:24:43 +0000	[diff] [blame]	572	<tr><td>FALSE</td>
				573	<td>FALSE</td>
				574	<td> -- b</td>
				575	<td>The boolean value FALSE (0) is pushed on to the stack.</td>
Brian Gaeke	9018148	2003-11-24 02:52:51 +0000	[diff] [blame]	576	</tr>
Misha Brukman	f39d5d6	2004-05-13 00:24:43 +0000	[diff] [blame]	577	<tr><td>TRUE</td>
				578	<td>TRUE</td>
				579	<td> -- b</td>
				580	<td>The boolean value TRUE (-1) is pushed on to the stack.</td>
Brian Gaeke	9018148	2003-11-24 02:52:51 +0000	[diff] [blame]	581	</tr>
Chris Lattner	45ab10c	2003-12-18 06:40:22 +0000	[diff] [blame]	582	<tr><td colspan="4"><b>BITWISE OPERATORS</b></td></tr>
				583	<tr>
Misha Brukman	f39d5d6	2004-05-13 00:24:43 +0000	[diff] [blame]	584	<td>Word</td>
				585	<td>Name</td>
				586	<td>Operation</td>
				587	<td>Description</td>
Chris Lattner	45ab10c	2003-12-18 06:40:22 +0000	[diff] [blame]	588	</tr>
Misha Brukman	f39d5d6	2004-05-13 00:24:43 +0000	[diff] [blame]	589	<tr><td><<</td>
				590	<td>SHL</td>
				591	<td>w1 w2 -- w1<<w2</td>
				592	<td>Two values (w1 and w2) are popped off the stack. The w2
Brian Gaeke	9018148	2003-11-24 02:52:51 +0000	[diff] [blame]	593	operand is shifted left by the number of bits given by the
				594	w1 operand. The result is pushed back to the stack.</td>
				595	</tr>
Misha Brukman	f39d5d6	2004-05-13 00:24:43 +0000	[diff] [blame]	596	<tr><td>>></td>
				597	<td>SHR</td>
				598	<td>w1 w2 -- w1>>w2</td>
				599	<td>Two values (w1 and w2) are popped off the stack. The w2
Brian Gaeke	9018148	2003-11-24 02:52:51 +0000	[diff] [blame]	600	operand is shifted right by the number of bits given by the
				601	w1 operand. The result is pushed back to the stack.</td>
				602	</tr>
Misha Brukman	f39d5d6	2004-05-13 00:24:43 +0000	[diff] [blame]	603	<tr><td>OR</td>
				604	<td>OR</td>
				605	<td>w1 w2 -- w2\|w1</td>
				606	<td>Two values (w1 and w2) are popped off the stack. The values
Brian Gaeke	9018148	2003-11-24 02:52:51 +0000	[diff] [blame]	607	are bitwise OR'd together and pushed back on the stack. This is
				608	not a logical OR. The sequence 1 2 OR yields 3 not 1.</td>
				609	</tr>
Misha Brukman	f39d5d6	2004-05-13 00:24:43 +0000	[diff] [blame]	610	<tr><td>AND</td>
				611	<td>AND</td>
				612	<td>w1 w2 -- w2&w1</td>
				613	<td>Two values (w1 and w2) are popped off the stack. The values
Brian Gaeke	9018148	2003-11-24 02:52:51 +0000	[diff] [blame]	614	are bitwise AND'd together and pushed back on the stack. This is
				615	not a logical AND. The sequence 1 2 AND yields 0 not 1.</td>
				616	</tr>
Misha Brukman	f39d5d6	2004-05-13 00:24:43 +0000	[diff] [blame]	617	<tr><td>XOR</td>
				618	<td>XOR</td>
				619	<td>w1 w2 -- w2^w1</td>
				620	<td>Two values (w1 and w2) are popped off the stack. The values
Brian Gaeke	9018148	2003-11-24 02:52:51 +0000	[diff] [blame]	621	are bitwise exclusive OR'd together and pushed back on the stack.
				622	For example, The sequence 1 3 XOR yields 2.</td>
				623	</tr>
Chris Lattner	45ab10c	2003-12-18 06:40:22 +0000	[diff] [blame]	624	<tr><td colspan="4"><b>ARITHMETIC OPERATORS</b></td></tr>
				625	<tr>
Misha Brukman	f39d5d6	2004-05-13 00:24:43 +0000	[diff] [blame]	626	<td>Word</td>
				627	<td>Name</td>
				628	<td>Operation</td>
				629	<td>Description</td>
Chris Lattner	45ab10c	2003-12-18 06:40:22 +0000	[diff] [blame]	630	</tr>
Misha Brukman	f39d5d6	2004-05-13 00:24:43 +0000	[diff] [blame]	631	<tr><td>ABS</td>
				632	<td>ABS</td>
				633	<td>w -- \|w\|</td>
				634	<td>One value s popped off the stack; its absolute value is computed
John Criswell	d000e1d	2003-12-18 16:43:17 +0000	[diff] [blame]	635	and then pushed on to the stack. If w1 is -1 then w2 is 1. If w1 is
Brian Gaeke	9018148	2003-11-24 02:52:51 +0000	[diff] [blame]	636	1 then w2 is also 1.</td>
				637	</tr>
Misha Brukman	f39d5d6	2004-05-13 00:24:43 +0000	[diff] [blame]	638	<tr><td>NEG</td>
				639	<td>NEG</td>
				640	<td>w -- -w</td>
				641	<td>One value is popped off the stack which is negated and then
John Criswell	d000e1d	2003-12-18 16:43:17 +0000	[diff] [blame]	642	pushed back on to the stack. If w1 is -1 then w2 is 1. If w1 is
Brian Gaeke	9018148	2003-11-24 02:52:51 +0000	[diff] [blame]	643	1 then w2 is -1.</td>
				644	</tr>
Misha Brukman	f39d5d6	2004-05-13 00:24:43 +0000	[diff] [blame]	645	<tr><td> + </td>
				646	<td>ADD</td>
				647	<td>w1 w2 -- w2+w1</td>
				648	<td>Two values are popped off the stack. Their sum is pushed back
John Criswell	d000e1d	2003-12-18 16:43:17 +0000	[diff] [blame]	649	on to the stack</td>
Brian Gaeke	9018148	2003-11-24 02:52:51 +0000	[diff] [blame]	650	</tr>
Misha Brukman	f39d5d6	2004-05-13 00:24:43 +0000	[diff] [blame]	651	<tr><td> - </td>
				652	<td>SUB</td>
				653	<td>w1 w2 -- w2-w1</td>
				654	<td>Two values are popped off the stack. Their difference is pushed back
John Criswell	d000e1d	2003-12-18 16:43:17 +0000	[diff] [blame]	655	on to the stack</td>
Brian Gaeke	9018148	2003-11-24 02:52:51 +0000	[diff] [blame]	656	</tr>
Misha Brukman	f39d5d6	2004-05-13 00:24:43 +0000	[diff] [blame]	657	<tr><td> * </td>
				658	<td>MUL</td>
				659	<td>w1 w2 -- w2*w1</td>
				660	<td>Two values are popped off the stack. Their product is pushed back
John Criswell	d000e1d	2003-12-18 16:43:17 +0000	[diff] [blame]	661	on to the stack</td>
Brian Gaeke	9018148	2003-11-24 02:52:51 +0000	[diff] [blame]	662	</tr>
Misha Brukman	f39d5d6	2004-05-13 00:24:43 +0000	[diff] [blame]	663	<tr><td> / </td>
				664	<td>DIV</td>
				665	<td>w1 w2 -- w2/w1</td>
				666	<td>Two values are popped off the stack. Their quotient is pushed back
John Criswell	d000e1d	2003-12-18 16:43:17 +0000	[diff] [blame]	667	on to the stack</td>
Brian Gaeke	9018148	2003-11-24 02:52:51 +0000	[diff] [blame]	668	</tr>
Misha Brukman	f39d5d6	2004-05-13 00:24:43 +0000	[diff] [blame]	669	<tr><td>MOD</td>
				670	<td>MOD</td>
				671	<td>w1 w2 -- w2%w1</td>
				672	<td>Two values are popped off the stack. Their remainder after division
John Criswell	d000e1d	2003-12-18 16:43:17 +0000	[diff] [blame]	673	of w1 by w2 is pushed back on to the stack</td>
Brian Gaeke	9018148	2003-11-24 02:52:51 +0000	[diff] [blame]	674	</tr>
Misha Brukman	f39d5d6	2004-05-13 00:24:43 +0000	[diff] [blame]	675	<tr><td> */ </td>
				676	<td>STAR_SLAH</td>
				677	<td>w1 w2 w3 -- (w3*w2)/w1</td>
				678	<td>Three values are popped off the stack. The product of w1 and w2 is
John Criswell	d000e1d	2003-12-18 16:43:17 +0000	[diff] [blame]	679	divided by w3. The result is pushed back on to the stack.</td>
Brian Gaeke	9018148	2003-11-24 02:52:51 +0000	[diff] [blame]	680	</tr>
Misha Brukman	f39d5d6	2004-05-13 00:24:43 +0000	[diff] [blame]	681	<tr><td> ++ </td>
				682	<td>INCR</td>
				683	<td>w -- w+1</td>
				684	<td>One value is popped off the stack. It is incremented by one and then
John Criswell	d000e1d	2003-12-18 16:43:17 +0000	[diff] [blame]	685	pushed back on to the stack.</td>
Brian Gaeke	9018148	2003-11-24 02:52:51 +0000	[diff] [blame]	686	</tr>
Misha Brukman	f39d5d6	2004-05-13 00:24:43 +0000	[diff] [blame]	687	<tr><td> -- </td>
				688	<td>DECR</td>
				689	<td>w -- w-1</td>
				690	<td>One value is popped off the stack. It is decremented by one and then
John Criswell	d000e1d	2003-12-18 16:43:17 +0000	[diff] [blame]	691	pushed back on to the stack.</td>
Brian Gaeke	9018148	2003-11-24 02:52:51 +0000	[diff] [blame]	692	</tr>
Misha Brukman	f39d5d6	2004-05-13 00:24:43 +0000	[diff] [blame]	693	<tr><td>MIN</td>
				694	<td>MIN</td>
				695	<td>w1 w2 -- (w2<w1?w2:w1)</td>
				696	<td>Two values are popped off the stack. The larger one is pushed back
John Criswell	d000e1d	2003-12-18 16:43:17 +0000	[diff] [blame]	697	on to the stack.</td>
Brian Gaeke	9018148	2003-11-24 02:52:51 +0000	[diff] [blame]	698	</tr>
Misha Brukman	f39d5d6	2004-05-13 00:24:43 +0000	[diff] [blame]	699	<tr><td>MAX</td>
				700	<td>MAX</td>
				701	<td>w1 w2 -- (w2>w1?w2:w1)</td>
				702	<td>Two values are popped off the stack. The larger value is pushed back
John Criswell	d000e1d	2003-12-18 16:43:17 +0000	[diff] [blame]	703	on to the stack.</td>
Brian Gaeke	9018148	2003-11-24 02:52:51 +0000	[diff] [blame]	704	</tr>
Chris Lattner	45ab10c	2003-12-18 06:40:22 +0000	[diff] [blame]	705	<tr><td colspan="4"><b>STACK MANIPULATION OPERATORS</b></td></tr>
				706	<tr>
Misha Brukman	f39d5d6	2004-05-13 00:24:43 +0000	[diff] [blame]	707	<td>Word</td>
				708	<td>Name</td>
				709	<td>Operation</td>
				710	<td>Description</td>
Brian Gaeke	9018148	2003-11-24 02:52:51 +0000	[diff] [blame]	711	</tr>
Misha Brukman	f39d5d6	2004-05-13 00:24:43 +0000	[diff] [blame]	712	<tr><td>DROP</td>
				713	<td>DROP</td>
				714	<td>w -- </td>
				715	<td>One value is popped off the stack.</td>
Brian Gaeke	9018148	2003-11-24 02:52:51 +0000	[diff] [blame]	716	</tr>
Misha Brukman	f39d5d6	2004-05-13 00:24:43 +0000	[diff] [blame]	717	<tr><td>DROP2</td>
				718	<td>DROP2</td>
				719	<td>w1 w2 -- </td>
				720	<td>Two values are popped off the stack.</td>
Chris Lattner	45ab10c	2003-12-18 06:40:22 +0000	[diff] [blame]	721	</tr>
Misha Brukman	f39d5d6	2004-05-13 00:24:43 +0000	[diff] [blame]	722	<tr><td>NIP</td>
				723	<td>NIP</td>
				724	<td>w1 w2 -- w2</td>
				725	<td>The second value on the stack is removed from the stack. That is,
Brian Gaeke	9018148	2003-11-24 02:52:51 +0000	[diff] [blame]	726	a value is popped off the stack and retained. Then a second value is
				727	popped and the retained value is pushed.</td>
				728	</tr>
Misha Brukman	f39d5d6	2004-05-13 00:24:43 +0000	[diff] [blame]	729	<tr><td>NIP2</td>
				730	<td>NIP2</td>
				731	<td>w1 w2 w3 w4 -- w3 w4</td>
				732	<td>The third and fourth values on the stack are removed from it. That is,
Brian Gaeke	9018148	2003-11-24 02:52:51 +0000	[diff] [blame]	733	two values are popped and retained. Then two more values are popped and
				734	the two retained values are pushed back on.</td>
				735	</tr>
Misha Brukman	f39d5d6	2004-05-13 00:24:43 +0000	[diff] [blame]	736	<tr><td>DUP</td>
				737	<td>DUP</td>
				738	<td>w1 -- w1 w1</td>
				739	<td>One value is popped off the stack. That value is then pushed on to
Brian Gaeke	9018148	2003-11-24 02:52:51 +0000	[diff] [blame]	740	the stack twice to duplicate the top stack vaue.</td>
				741	</tr>
Misha Brukman	f39d5d6	2004-05-13 00:24:43 +0000	[diff] [blame]	742	<tr><td>DUP2</td>
				743	<td>DUP2</td>
				744	<td>w1 w2 -- w1 w2 w1 w2</td>
				745	<td>The top two values on the stack are duplicated. That is, two vaues
Brian Gaeke	9018148	2003-11-24 02:52:51 +0000	[diff] [blame]	746	are popped off the stack. They are alternately pushed back on the
				747	stack twice each.</td>
				748	</tr>
Misha Brukman	f39d5d6	2004-05-13 00:24:43 +0000	[diff] [blame]	749	<tr><td>SWAP</td>
				750	<td>SWAP</td>
				751	<td>w1 w2 -- w2 w1</td>
				752	<td>The top two stack items are reversed in their order. That is, two
John Criswell	d000e1d	2003-12-18 16:43:17 +0000	[diff] [blame]	753	values are popped off the stack and pushed back on to the stack in
Brian Gaeke	9018148	2003-11-24 02:52:51 +0000	[diff] [blame]	754	the opposite order they were popped.</td>
				755	</tr>
Misha Brukman	f39d5d6	2004-05-13 00:24:43 +0000	[diff] [blame]	756	<tr><td>SWAP2</td>
				757	<td>SWAP2</td>
				758	<td>w1 w2 w3 w4 -- w3 w4 w2 w1</td>
				759	<td>The top four stack items are swapped in pairs. That is, two values
Brian Gaeke	9018148	2003-11-24 02:52:51 +0000	[diff] [blame]	760	are popped and retained. Then, two more values are popped and retained.
John Criswell	d000e1d	2003-12-18 16:43:17 +0000	[diff] [blame]	761	The values are pushed back on to the stack in the reverse order but
Misha Brukman	3669299	2004-05-12 19:52:00 +0000	[diff] [blame]	762	in pairs.</td>
Brian Gaeke	9018148	2003-11-24 02:52:51 +0000	[diff] [blame]	763	</tr>
Misha Brukman	f39d5d6	2004-05-13 00:24:43 +0000	[diff] [blame]	764	<tr><td>OVER</td>
				765	<td>OVER</td>
				766	<td>w1 w2-- w1 w2 w1</td>
				767	<td>Two values are popped from the stack. They are pushed back
John Criswell	d000e1d	2003-12-18 16:43:17 +0000	[diff] [blame]	768	on to the stack in the order w1 w2 w1. This seems to cause the
Brian Gaeke	9018148	2003-11-24 02:52:51 +0000	[diff] [blame]	769	top stack element to be duplicated "over" the next value.</td>
				770	</tr>
Misha Brukman	f39d5d6	2004-05-13 00:24:43 +0000	[diff] [blame]	771	<tr><td>OVER2</td>
				772	<td>OVER2</td>
				773	<td>w1 w2 w3 w4 -- w1 w2 w3 w4 w1 w2</td>
				774	<td>The third and fourth values on the stack are replicated on to the
Brian Gaeke	9018148	2003-11-24 02:52:51 +0000	[diff] [blame]	775	top of the stack</td>
				776	</tr>
Misha Brukman	f39d5d6	2004-05-13 00:24:43 +0000	[diff] [blame]	777	<tr><td>ROT</td>
				778	<td>ROT</td>
				779	<td>w1 w2 w3 -- w2 w3 w1</td>
				780	<td>The top three values are rotated. That is, three value are popped
John Criswell	d000e1d	2003-12-18 16:43:17 +0000	[diff] [blame]	781	off the stack. They are pushed back on to the stack in the order
Brian Gaeke	9018148	2003-11-24 02:52:51 +0000	[diff] [blame]	782	w1 w3 w2.</td>
				783	</tr>
Misha Brukman	f39d5d6	2004-05-13 00:24:43 +0000	[diff] [blame]	784	<tr><td>ROT2</td>
				785	<td>ROT2</td>
				786	<td>w1 w2 w3 w4 w5 w6 -- w3 w4 w5 w6 w1 w2</td>
				787	<td>Like ROT but the rotation is done using three pairs instead of
Brian Gaeke	9018148	2003-11-24 02:52:51 +0000	[diff] [blame]	788	three singles.</td>
				789	</tr>
Misha Brukman	f39d5d6	2004-05-13 00:24:43 +0000	[diff] [blame]	790	<tr><td>RROT</td>
				791	<td>RROT</td>
				792	<td>w1 w2 w3 -- w2 w3 w1</td>
				793	<td>Reverse rotation. Like ROT, but it rotates the other way around.
Brian Gaeke	9018148	2003-11-24 02:52:51 +0000	[diff] [blame]	794	Essentially, the third element on the stack is moved to the top
				795	of the stack.</td>
				796	</tr>
Misha Brukman	f39d5d6	2004-05-13 00:24:43 +0000	[diff] [blame]	797	<tr><td>RROT2</td>
				798	<td>RROT2</td>
				799	<td>w1 w2 w3 w4 w5 w6 -- w3 w4 w5 w6 w1 w2</td>
				800	<td>Double reverse rotation. Like RROT but the rotation is done using
Brian Gaeke	9018148	2003-11-24 02:52:51 +0000	[diff] [blame]	801	three pairs instead of three singles. The fifth and sixth stack
				802	elements are moved to the first and second positions</td>
				803	</tr>
Misha Brukman	f39d5d6	2004-05-13 00:24:43 +0000	[diff] [blame]	804	<tr><td>TUCK</td>
				805	<td>TUCK</td>
				806	<td>w1 w2 -- w2 w1 w2</td>
				807	<td>Similar to OVER except that the second operand is being
Brian Gaeke	9018148	2003-11-24 02:52:51 +0000	[diff] [blame]	808	replicated. Essentially, the first operand is being "tucked"
				809	in between two instances of the second operand. Logically, two
				810	values are popped off the stack. They are placed back on the
				811	stack in the order w2 w1 w2.</td>
				812	</tr>
Misha Brukman	f39d5d6	2004-05-13 00:24:43 +0000	[diff] [blame]	813	<tr><td>TUCK2</td>
				814	<td>TUCK2</td>
				815	<td>w1 w2 w3 w4 -- w3 w4 w1 w2 w3 w4</td>
				816	<td>Like TUCK but a pair of elements is tucked over two pairs.
Brian Gaeke	9018148	2003-11-24 02:52:51 +0000	[diff] [blame]	817	That is, the top two elements of the stack are duplicated and
				818	inserted into the stack at the fifth and positions.</td>
				819	</tr>
Misha Brukman	f39d5d6	2004-05-13 00:24:43 +0000	[diff] [blame]	820	<tr><td>PICK</td>
				821	<td>PICK</td>
				822	<td>x0 ... Xn n -- x0 ... Xn x0</td>
				823	<td>The top of the stack is used as an index into the remainder of
Brian Gaeke	9018148	2003-11-24 02:52:51 +0000	[diff] [blame]	824	the stack. The element at the nth position replaces the index
				825	(top of stack). This is useful for cycling through a set of
				826	values. Note that indexing is zero based. So, if n=0 then you
				827	get the second item on the stack. If n=1 you get the third, etc.
				828	Note also that the index is replaced by the n'th value. </td>
				829	</tr>
Misha Brukman	f39d5d6	2004-05-13 00:24:43 +0000	[diff] [blame]	830	<tr><td>SELECT</td>
				831	<td>SELECT</td>
				832	<td>m n X0..Xm Xm+1 .. Xn -- Xm</td>
				833	<td>This is like PICK but the list is removed and you need to specify
Brian Gaeke	9018148	2003-11-24 02:52:51 +0000	[diff] [blame]	834	both the index and the size of the list. Careful with this one,
				835	the wrong value for n can blow away a huge amount of the stack.</td>
				836	</tr>
Misha Brukman	f39d5d6	2004-05-13 00:24:43 +0000	[diff] [blame]	837	<tr><td>ROLL</td>
				838	<td>ROLL</td>
				839	<td>x0 x1 .. xn n -- x1 .. xn x0</td>
				840	<td><b>Not Implemented</b>. This one has been left as an exercise to
Chris Lattner	e46d601	2003-11-25 01:35:06 +0000	[diff] [blame]	841	the student. See <a href="#exercise">Exercise</a>. ROLL requires
				842	a value, "n", to be on the top of the stack. This value specifies how
				843	far into the stack to "roll". The n'th value is <em>moved</em> (not
				844	copied) from its location and replaces the "n" value on the top of the
				845	stack. In this way, all the values between "n" and x0 roll up the stack.
				846	The operation of ROLL is a generalized ROT. The "n" value specifies
				847	how much to rotate. That is, ROLL with n=1 is the same as ROT and
				848	ROLL with n=2 is the same as ROT2.</td>
Brian Gaeke	9018148	2003-11-24 02:52:51 +0000	[diff] [blame]	849	</tr>
Chris Lattner	45ab10c	2003-12-18 06:40:22 +0000	[diff] [blame]	850	<tr><td colspan="4"><b>MEMORY OPERATORS</b></td></tr>
				851	<tr>
Misha Brukman	f39d5d6	2004-05-13 00:24:43 +0000	[diff] [blame]	852	<td>Word</td>
				853	<td>Name</td>
				854	<td>Operation</td>
				855	<td>Description</td>
Chris Lattner	45ab10c	2003-12-18 06:40:22 +0000	[diff] [blame]	856	</tr>
Misha Brukman	f39d5d6	2004-05-13 00:24:43 +0000	[diff] [blame]	857	<tr><td>MALLOC</td>
				858	<td>MALLOC</td>
				859	<td>w1 -- p</td>
				860	<td>One value is popped off the stack. The value is used as the size
Brian Gaeke	9018148	2003-11-24 02:52:51 +0000	[diff] [blame]	861	of a memory block to allocate. The size is in bytes, not words.
				862	The memory allocation is completed and the address of the memory
John Criswell	d000e1d	2003-12-18 16:43:17 +0000	[diff] [blame]	863	block is pushed on to the stack.</td>
Brian Gaeke	9018148	2003-11-24 02:52:51 +0000	[diff] [blame]	864	</tr>
Misha Brukman	f39d5d6	2004-05-13 00:24:43 +0000	[diff] [blame]	865	<tr><td>FREE</td>
				866	<td>FREE</td>
				867	<td>p -- </td>
				868	<td>One pointer value is popped off the stack. The value should be
Brian Gaeke	9018148	2003-11-24 02:52:51 +0000	[diff] [blame]	869	the address of a memory block created by the MALLOC operation. The
				870	associated memory block is freed. Nothing is pushed back on the
				871	stack. Many bugs can be created by attempting to FREE something
				872	that isn't a pointer to a MALLOC allocated memory block. Make
				873	sure you know what's on the stack. One way to do this is with
				874	the following idiom:<br/>
				875	<code>64 MALLOC DUP DUP (use ptr) DUP (use ptr) ... FREE</code>
				876	<br/>This ensures that an extra copy of the pointer is placed on
				877	the stack (for the FREE at the end) and that every use of the
				878	pointer is preceded by a DUP to retain the copy for FREE.</td>
				879	</tr>
Misha Brukman	f39d5d6	2004-05-13 00:24:43 +0000	[diff] [blame]	880	<tr><td>GET</td>
				881	<td>GET</td>
				882	<td>w1 p -- w2 p</td>
				883	<td>An integer index and a pointer to a memory block are popped of
Brian Gaeke	9018148	2003-11-24 02:52:51 +0000	[diff] [blame]	884	the block. The index is used to index one byte from the memory
				885	block. That byte value is retained, the pointer is pushed again
				886	and the retained value is pushed. Note that the pointer value
				887	s essentially retained in its position so this doesn't count
				888	as a "use ptr" in the FREE idiom.</td>
				889	</tr>
Misha Brukman	f39d5d6	2004-05-13 00:24:43 +0000	[diff] [blame]	890	<tr><td>PUT</td>
				891	<td>PUT</td>
				892	<td>w1 w2 p -- p </td>
				893	<td>An integer value is popped of the stack. This is the value to
Brian Gaeke	9018148	2003-11-24 02:52:51 +0000	[diff] [blame]	894	be put into a memory block. Another integer value is popped of
				895	the stack. This is the indexed byte in the memory block. A
				896	pointer to the memory block is popped off the stack. The
				897	first value (w1) is then converted to a byte and written
				898	to the element of the memory block(p) at the index given
				899	by the second value (w2). The pointer to the memory block is
				900	pushed back on the stack so this doesn't count as a "use ptr"
				901	in the FREE idiom.</td>
				902	</tr>
Chris Lattner	45ab10c	2003-12-18 06:40:22 +0000	[diff] [blame]	903	<tr><td colspan="4"><b>CONTROL FLOW OPERATORS</b></td></tr>
				904	<tr>
Misha Brukman	f39d5d6	2004-05-13 00:24:43 +0000	[diff] [blame]	905	<td>Word</td>
				906	<td>Name</td>
				907	<td>Operation</td>
				908	<td>Description</td>
Chris Lattner	45ab10c	2003-12-18 06:40:22 +0000	[diff] [blame]	909	</tr>
Misha Brukman	f39d5d6	2004-05-13 00:24:43 +0000	[diff] [blame]	910	<tr><td>RETURN</td>
				911	<td>RETURN</td>
				912	<td> -- </td>
				913	<td>The currently executing definition returns immediately to its caller.
Brian Gaeke	9018148	2003-11-24 02:52:51 +0000	[diff] [blame]	914	Note that there is an implicit <code>RETURN</code> at the end of each
				915	definition, logically located at the semi-colon. The sequence
				916	<code>RETURN ;</code> is valid but redundant.</td>
				917	</tr>
Misha Brukman	f39d5d6	2004-05-13 00:24:43 +0000	[diff] [blame]	918	<tr><td>EXIT</td>
				919	<td>EXIT</td>
				920	<td>w1 -- </td>
				921	<td>A return value for the program is popped off the stack. The program is
Brian Gaeke	9018148	2003-11-24 02:52:51 +0000	[diff] [blame]	922	then immediately terminated. This is normally an abnormal exit from the
				923	program. For a normal exit (when <code>MAIN</code> finishes), the exit
				924	code will always be zero in accordance with UNIX conventions.</td>
				925	</tr>
Misha Brukman	f39d5d6	2004-05-13 00:24:43 +0000	[diff] [blame]	926	<tr><td>RECURSE</td>
				927	<td>RECURSE</td>
				928	<td> -- </td>
				929	<td>The currently executed definition is called again. This operation is
Brian Gaeke	9018148	2003-11-24 02:52:51 +0000	[diff] [blame]	930	needed since the definition of a word doesn't exist until the semi colon
				931	is reacher. Attempting something like:<br/>
				932	<code> : recurser recurser ; </code><br/> will yield and error saying that
				933	"recurser" is not defined yet. To accomplish the same thing, change this
				934	to:<br/>
				935	<code> : recurser RECURSE ; </code></td>
				936	</tr>
Misha Brukman	f39d5d6	2004-05-13 00:24:43 +0000	[diff] [blame]	937	<tr><td>IF (words...) ENDIF</td>
				938	<td>IF (words...) ENDIF</td>
				939	<td>b -- </td>
				940	<td>A boolean value is popped of the stack. If it is non-zero then the "words..."
Brian Gaeke	9018148	2003-11-24 02:52:51 +0000	[diff] [blame]	941	are executed. Otherwise, execution continues immediately following the ENDIF.</td>
				942	</tr>
Misha Brukman	f39d5d6	2004-05-13 00:24:43 +0000	[diff] [blame]	943	<tr><td>IF (words...) ELSE (words...) ENDIF</td>
				944	<td>IF (words...) ELSE (words...) ENDIF</td>
				945	<td>b -- </td>
				946	<td>A boolean value is popped of the stack. If it is non-zero then the "words..."
Brian Gaeke	9018148	2003-11-24 02:52:51 +0000	[diff] [blame]	947	between IF and ELSE are executed. Otherwise the words between ELSE and ENDIF are
				948	executed. In either case, after the (words....) have executed, execution continues
				949	immediately following the ENDIF. </td>
				950	</tr>
Misha Brukman	f39d5d6	2004-05-13 00:24:43 +0000	[diff] [blame]	951	<tr><td>WHILE (words...) END</td>
				952	<td>WHILE (words...) END</td>
				953	<td>b -- b </td>
				954	<td>The boolean value on the top of the stack is examined. If it is non-zero then the
Brian Gaeke	9018148	2003-11-24 02:52:51 +0000	[diff] [blame]	955	"words..." between WHILE and END are executed. Execution then begins again at the WHILE where another
				956	boolean is popped off the stack. To prevent this operation from eating up the entire
John Criswell	d000e1d	2003-12-18 16:43:17 +0000	[diff] [blame]	957	stack, you should push on to the stack (just before the END) a boolean value that indicates
Brian Gaeke	9018148	2003-11-24 02:52:51 +0000	[diff] [blame]	958	whether to terminate. Note that since booleans and integers can be coerced you can
				959	use the following "for loop" idiom:<br/>
				960	<code>(push count) WHILE (words...) -- END</code><br/>
				961	For example:<br/>
				962	<code>10 WHILE DUP >d -- END</code><br/>
				963	This will print the numbers from 10 down to 1. 10 is pushed on the stack. Since that is
				964	non-zero, the while loop is entered. The top of the stack (10) is duplicated and then
				965	printed out with >d. The top of the stack is decremented, yielding 9 and control is
				966	transfered back to the WHILE keyword. The process starts all over again and repeats until
				967	the top of stack is decremented to 0 at which the WHILE test fails and control is
				968	transfered to the word after the END.</td>
				969	</tr>
Chris Lattner	45ab10c	2003-12-18 06:40:22 +0000	[diff] [blame]	970	<tr><td colspan="4"><b>INPUT & OUTPUT OPERATORS</b></td></tr>
				971	<tr>
Misha Brukman	f39d5d6	2004-05-13 00:24:43 +0000	[diff] [blame]	972	<td>Word</td>
				973	<td>Name</td>
				974	<td>Operation</td>
				975	<td>Description</td>
Brian Gaeke	9018148	2003-11-24 02:52:51 +0000	[diff] [blame]	976	</tr>
Misha Brukman	f39d5d6	2004-05-13 00:24:43 +0000	[diff] [blame]	977	<tr><td>SPACE</td>
				978	<td>SPACE</td>
				979	<td> -- </td>
				980	<td>A space character is put out. There is no stack effect.</td>
Brian Gaeke	9018148	2003-11-24 02:52:51 +0000	[diff] [blame]	981	</tr>
Misha Brukman	f39d5d6	2004-05-13 00:24:43 +0000	[diff] [blame]	982	<tr><td>TAB</td>
				983	<td>TAB</td>
				984	<td> -- </td>
				985	<td>A tab character is put out. There is no stack effect.</td>
Brian Gaeke	9018148	2003-11-24 02:52:51 +0000	[diff] [blame]	986	</tr>
Misha Brukman	f39d5d6	2004-05-13 00:24:43 +0000	[diff] [blame]	987	<tr><td>CR</td>
				988	<td>CR</td>
				989	<td> -- </td>
				990	<td>A carriage return character is put out. There is no stack effect.</td>
Brian Gaeke	9018148	2003-11-24 02:52:51 +0000	[diff] [blame]	991	</tr>
Misha Brukman	f39d5d6	2004-05-13 00:24:43 +0000	[diff] [blame]	992	<tr><td>>s</td>
				993	<td>OUT_STR</td>
				994	<td> -- </td>
				995	<td>A string pointer is popped from the stack. It is put out.</td>
Brian Gaeke	9018148	2003-11-24 02:52:51 +0000	[diff] [blame]	996	</tr>
Misha Brukman	f39d5d6	2004-05-13 00:24:43 +0000	[diff] [blame]	997	<tr><td>>d</td>
				998	<td>OUT_STR</td>
				999	<td> -- </td>
				1000	<td>A value is popped from the stack. It is put out as a decimal
				1001	integer.</td>
Brian Gaeke	9018148	2003-11-24 02:52:51 +0000	[diff] [blame]	1002	</tr>
Misha Brukman	f39d5d6	2004-05-13 00:24:43 +0000	[diff] [blame]	1003	<tr><td>>c</td>
				1004	<td>OUT_CHR</td>
				1005	<td> -- </td>
				1006	<td>A value is popped from the stack. It is put out as an ASCII
				1007	character.</td>
Chris Lattner	45ab10c	2003-12-18 06:40:22 +0000	[diff] [blame]	1008	</tr>
Misha Brukman	f39d5d6	2004-05-13 00:24:43 +0000	[diff] [blame]	1009	<tr><td><s</td>
				1010	<td>IN_STR</td>
				1011	<td> -- s </td>
				1012	<td>A string is read from the input via the scanf(3) format string " %as".
				1013	The resulting string is pushed on to the stack.</td>
Brian Gaeke	9018148	2003-11-24 02:52:51 +0000	[diff] [blame]	1014	</tr>
Misha Brukman	f39d5d6	2004-05-13 00:24:43 +0000	[diff] [blame]	1015	<tr><td><d</td>
				1016	<td>IN_STR</td>
				1017	<td> -- w </td>
				1018	<td>An integer is read from the input via the scanf(3) format string " %d".
				1019	The resulting value is pushed on to the stack</td>
Brian Gaeke	9018148	2003-11-24 02:52:51 +0000	[diff] [blame]	1020	</tr>
Misha Brukman	f39d5d6	2004-05-13 00:24:43 +0000	[diff] [blame]	1021	<tr><td><c</td>
				1022	<td>IN_CHR</td>
				1023	<td> -- w </td>
				1024	<td>A single character is read from the input via the scanf(3) format string
				1025	" %c". The value is converted to an integer and pushed on to the stack.</td>
Brian Gaeke	9018148	2003-11-24 02:52:51 +0000	[diff] [blame]	1026	</tr>
Misha Brukman	f39d5d6	2004-05-13 00:24:43 +0000	[diff] [blame]	1027	<tr><td>DUMP</td>
				1028	<td>DUMP</td>
				1029	<td> -- </td>
				1030	<td>The stack contents are dumped to standard output. This is useful for
Brian Gaeke	9018148	2003-11-24 02:52:51 +0000	[diff] [blame]	1031	debugging your definitions. Put DUMP at the beginning and end of a definition
				1032	to see instantly the net effect of the definition.</td>
				1033	</tr>
				1034	</table>
Misha Brukman	fd90f88	2004-05-13 00:37:23 +0000	[diff] [blame]	1035
Brian Gaeke	9018148	2003-11-24 02:52:51 +0000	[diff] [blame]	1036	</div>
				1037	<!-- ======================================================================= -->
Brian Gaeke	07e89e4	2003-11-24 17:03:38 +0000	[diff] [blame]	1038	<div class="doc_section"> <a name="example">Prime: A Complete Example</a></div>
Brian Gaeke	9018148	2003-11-24 02:52:51 +0000	[diff] [blame]	1039	<div class="doc_text">
Brian Gaeke	07e89e4	2003-11-24 17:03:38 +0000	[diff] [blame]	1040	<p>The following fully documented program highlights many features of both
				1041	the Stacker language and what is possible with LLVM. The program has two modes
John Criswell	d000e1d	2003-12-18 16:43:17 +0000	[diff] [blame]	1042	of operation. If you provide numeric arguments to the program, it checks to see
Chris Lattner	45ab10c	2003-12-18 06:40:22 +0000	[diff] [blame]	1043	if those arguments are prime numbers and prints out the results. Without any
John Criswell	d000e1d	2003-12-18 16:43:17 +0000	[diff] [blame]	1044	arguments, the program prints out any prime numbers it finds between 1 and one
Chris Lattner	45ab10c	2003-12-18 06:40:22 +0000	[diff] [blame]	1045	million (there's a lot of them!). The source code comments below tell the
Brian Gaeke	07e89e4	2003-11-24 17:03:38 +0000	[diff] [blame]	1046	remainder of the story.
Brian Gaeke	9018148	2003-11-24 02:52:51 +0000	[diff] [blame]	1047	</p>
				1048	</div>
				1049	<div class="doc_text">
Brian Gaeke	07e89e4	2003-11-24 17:03:38 +0000	[diff] [blame]	1050	<pre><code>
Brian Gaeke	9018148	2003-11-24 02:52:51 +0000	[diff] [blame]	1051	################################################################################
				1052	#
				1053	# Brute force prime number generator
				1054	#
				1055	# This program is written in classic Stacker style, that being the style of a
				1056	# stack. Start at the bottom and read your way up !
				1057	#
				1058	# Reid Spencer - Nov 2003
				1059	################################################################################
				1060	# Utility definitions
				1061	################################################################################
Misha Brukman	f39d5d6	2004-05-13 00:24:43 +0000	[diff] [blame]	1062	: print >d CR ;
Brian Gaeke	9018148	2003-11-24 02:52:51 +0000	[diff] [blame]	1063	: it_is_a_prime TRUE ;
				1064	: it_is_not_a_prime FALSE ;
				1065	: continue_loop TRUE ;
				1066	: exit_loop FALSE;
				1067
				1068	################################################################################
John Criswell	d000e1d	2003-12-18 16:43:17 +0000	[diff] [blame]	1069	# This definition tries an actual division of a candidate prime number. It
Brian Gaeke	9018148	2003-11-24 02:52:51 +0000	[diff] [blame]	1070	# determines whether the division loop on this candidate should continue or
				1071	# not.
Misha Brukman	f39d5d6	2004-05-13 00:24:43 +0000	[diff] [blame]	1072	# STACK<:
Brian Gaeke	9018148	2003-11-24 02:52:51 +0000	[diff] [blame]	1073	# div - the divisor to try
				1074	# p - the prime number we are working on
Misha Brukman	f39d5d6	2004-05-13 00:24:43 +0000	[diff] [blame]	1075	# STACK>:
Brian Gaeke	9018148	2003-11-24 02:52:51 +0000	[diff] [blame]	1076	# cont - should we continue the loop ?
				1077	# div - the next divisor to try
				1078	# p - the prime number we are working on
				1079	################################################################################
				1080	: try_dividing
				1081	DUP2 ( save div and p )
				1082	SWAP ( swap to put divisor second on stack)
				1083	MOD 0 = ( get remainder after division and test for 0 )
				1084	IF
				1085	exit_loop ( remainder = 0, time to exit )
				1086	ELSE
				1087	continue_loop ( remainder != 0, keep going )
				1088	ENDIF
				1089	;
				1090
				1091	################################################################################
				1092	# This function tries one divisor by calling try_dividing. But, before doing
				1093	# that it checks to see if the value is 1. If it is, it does not bother with
				1094	# the division because prime numbers are allowed to be divided by one. The
				1095	# top stack value (cont) is set to determine if the loop should continue on
				1096	# this prime number or not.
				1097	# STACK<:
				1098	# cont - should we continue the loop (ignored)?
				1099	# div - the divisor to try
				1100	# p - the prime number we are working on
Misha Brukman	f39d5d6	2004-05-13 00:24:43 +0000	[diff] [blame]	1101	# STACK>:
Brian Gaeke	9018148	2003-11-24 02:52:51 +0000	[diff] [blame]	1102	# cont - should we continue the loop ?
				1103	# div - the next divisor to try
				1104	# p - the prime number we are working on
				1105	################################################################################
				1106	: try_one_divisor
				1107	DROP ( drop the loop continuation )
				1108	DUP ( save the divisor )
				1109	1 = IF ( see if divisor is == 1 )
				1110	exit_loop ( no point dividing by 1 )
				1111	ELSE
				1112	try_dividing ( have to keep going )
				1113	ENDIF
				1114	SWAP ( get divisor on top )
				1115	-- ( decrement it )
				1116	SWAP ( put loop continuation back on top )
				1117	;
				1118
				1119	################################################################################
				1120	# The number on the stack (p) is a candidate prime number that we must test to
				1121	# determine if it really is a prime number. To do this, we divide it by every
				1122	# number from one p-1 to 1. The division is handled in the try_one_divisor
				1123	# definition which returns a loop continuation value (which we also seed with
				1124	# the value 1). After the loop, we check the divisor. If it decremented all
				1125	# the way to zero then we found a prime, otherwise we did not find one.
Misha Brukman	f39d5d6	2004-05-13 00:24:43 +0000	[diff] [blame]	1126	# STACK<:
Brian Gaeke	9018148	2003-11-24 02:52:51 +0000	[diff] [blame]	1127	# p - the prime number to check
Misha Brukman	f39d5d6	2004-05-13 00:24:43 +0000	[diff] [blame]	1128	# STACK>:
John Criswell	d000e1d	2003-12-18 16:43:17 +0000	[diff] [blame]	1129	# yn - boolean indicating if its a prime or not
Brian Gaeke	9018148	2003-11-24 02:52:51 +0000	[diff] [blame]	1130	# p - the prime number checked
				1131	################################################################################
				1132	: try_harder
				1133	DUP ( duplicate to get divisor value ) )
				1134	-- ( first divisor is one less than p )
				1135	1 ( continue the loop )
				1136	WHILE
				1137	try_one_divisor ( see if its prime )
				1138	END
				1139	DROP ( drop the continuation value )
				1140	0 = IF ( test for divisor == 1 )
				1141	it_is_a_prime ( we found one )
				1142	ELSE
				1143	it_is_not_a_prime ( nope, this one is not a prime )
				1144	ENDIF
				1145	;
				1146
				1147	################################################################################
				1148	# This definition determines if the number on the top of the stack is a prime
Misha Brukman	f39d5d6	2004-05-13 00:24:43 +0000	[diff] [blame]	1149	# or not. It does this by testing if the value is degenerate (<= 3) and
Brian Gaeke	9018148	2003-11-24 02:52:51 +0000	[diff] [blame]	1150	# responding with yes, its a prime. Otherwise, it calls try_harder to actually
				1151	# make some calculations to determine its primeness.
Misha Brukman	f39d5d6	2004-05-13 00:24:43 +0000	[diff] [blame]	1152	# STACK<:
Brian Gaeke	9018148	2003-11-24 02:52:51 +0000	[diff] [blame]	1153	# p - the prime number to check
Misha Brukman	f39d5d6	2004-05-13 00:24:43 +0000	[diff] [blame]	1154	# STACK>:
Brian Gaeke	9018148	2003-11-24 02:52:51 +0000	[diff] [blame]	1155	# yn - boolean indicating if its a prime or not
				1156	# p - the prime number checked
				1157	################################################################################
				1158	: is_prime
				1159	DUP ( save the prime number )
Misha Brukman	f39d5d6	2004-05-13 00:24:43 +0000	[diff] [blame]	1160	3 >= IF ( see if its <= 3 )
Brian Gaeke	9018148	2003-11-24 02:52:51 +0000	[diff] [blame]	1161	it_is_a_prime ( its <= 3 just indicate its prime )
				1162	ELSE
				1163	try_harder ( have to do a little more work )
				1164	ENDIF
				1165	;
				1166
				1167	################################################################################
				1168	# This definition is called when it is time to exit the program, after we have
				1169	# found a sufficiently large number of primes.
Misha Brukman	f39d5d6	2004-05-13 00:24:43 +0000	[diff] [blame]	1170	# STACK<: ignored
				1171	# STACK>: exits
Brian Gaeke	9018148	2003-11-24 02:52:51 +0000	[diff] [blame]	1172	################################################################################
				1173	: done
Misha Brukman	f39d5d6	2004-05-13 00:24:43 +0000	[diff] [blame]	1174	"Finished" >s CR ( say we are finished )
Brian Gaeke	9018148	2003-11-24 02:52:51 +0000	[diff] [blame]	1175	0 EXIT ( exit nicely )
				1176	;
				1177
				1178	################################################################################
				1179	# This definition checks to see if the candidate is greater than the limit. If
				1180	# it is, it terminates the program by calling done. Otherwise, it increments
				1181	# the value and calls is_prime to determine if the candidate is a prime or not.
				1182	# If it is a prime, it prints it. Note that the boolean result from is_prime is
				1183	# gobbled by the following IF which returns the stack to just contining the
				1184	# prime number just considered.
Misha Brukman	f39d5d6	2004-05-13 00:24:43 +0000	[diff] [blame]	1185	# STACK<:
Brian Gaeke	9018148	2003-11-24 02:52:51 +0000	[diff] [blame]	1186	# p - one less than the prime number to consider
Misha Brukman	f39d5d6	2004-05-13 00:24:43 +0000	[diff] [blame]	1187	# STAC>K
Brian Gaeke	9018148	2003-11-24 02:52:51 +0000	[diff] [blame]	1188	# p+1 - the prime number considered
				1189	################################################################################
				1190	: consider_prime
				1191	DUP ( save the prime number to consider )
Misha Brukman	f39d5d6	2004-05-13 00:24:43 +0000	[diff] [blame]	1192	1000000 < IF ( check to see if we are done yet )
Brian Gaeke	9018148	2003-11-24 02:52:51 +0000	[diff] [blame]	1193	done ( we are done, call "done" )
				1194	ENDIF
				1195	++ ( increment to next prime number )
				1196	is_prime ( see if it is a prime )
				1197	IF
				1198	print ( it is, print it )
				1199	ENDIF
				1200	;
				1201
				1202	################################################################################
				1203	# This definition starts at one, prints it out and continues into a loop calling
				1204	# consider_prime on each iteration. The prime number candidate we are looking at
				1205	# is incremented by consider_prime.
Misha Brukman	f39d5d6	2004-05-13 00:24:43 +0000	[diff] [blame]	1206	# STACK<: empty
				1207	# STACK>: empty
Brian Gaeke	9018148	2003-11-24 02:52:51 +0000	[diff] [blame]	1208	################################################################################
				1209	: find_primes
Misha Brukman	f39d5d6	2004-05-13 00:24:43 +0000	[diff] [blame]	1210	"Prime Numbers: " >s CR ( say hello )
Brian Gaeke	9018148	2003-11-24 02:52:51 +0000	[diff] [blame]	1211	DROP ( get rid of that pesky string )
				1212	1 ( stoke the fires )
				1213	print ( print the first one, we know its prime )
				1214	WHILE ( loop while the prime to consider is non zero )
				1215	consider_prime ( consider one prime number )
				1216	END
				1217	;
				1218
				1219	################################################################################
				1220	#
				1221	################################################################################
				1222	: say_yes
Misha Brukman	f39d5d6	2004-05-13 00:24:43 +0000	[diff] [blame]	1223	>d ( Print the prime number )
Brian Gaeke	9018148	2003-11-24 02:52:51 +0000	[diff] [blame]	1224	" is prime." ( push string to output )
Misha Brukman	f39d5d6	2004-05-13 00:24:43 +0000	[diff] [blame]	1225	>s ( output it )
Brian Gaeke	9018148	2003-11-24 02:52:51 +0000	[diff] [blame]	1226	CR ( print carriage return )
				1227	DROP ( pop string )
				1228	;
				1229
				1230	: say_no
Misha Brukman	f39d5d6	2004-05-13 00:24:43 +0000	[diff] [blame]	1231	>d ( Print the prime number )
Brian Gaeke	9018148	2003-11-24 02:52:51 +0000	[diff] [blame]	1232	" is NOT prime." ( push string to put out )
Misha Brukman	f39d5d6	2004-05-13 00:24:43 +0000	[diff] [blame]	1233	>s ( put out the string )
Brian Gaeke	9018148	2003-11-24 02:52:51 +0000	[diff] [blame]	1234	CR ( print carriage return )
				1235	DROP ( pop string )
				1236	;
				1237
				1238	################################################################################
				1239	# This definition processes a single command line argument and determines if it
				1240	# is a prime number or not.
Misha Brukman	f39d5d6	2004-05-13 00:24:43 +0000	[diff] [blame]	1241	# STACK<:
Brian Gaeke	9018148	2003-11-24 02:52:51 +0000	[diff] [blame]	1242	# n - number of arguments
				1243	# arg1 - the prime numbers to examine
Misha Brukman	f39d5d6	2004-05-13 00:24:43 +0000	[diff] [blame]	1244	# STACK>:
Brian Gaeke	9018148	2003-11-24 02:52:51 +0000	[diff] [blame]	1245	# n-1 - one less than number of arguments
				1246	# arg2 - we processed one argument
				1247	################################################################################
				1248	: do_one_argument
				1249	-- ( decrement loop counter )
				1250	SWAP ( get the argument value )
				1251	is_prime IF ( determine if its prime )
				1252	say_yes ( uhuh )
				1253	ELSE
				1254	say_no ( nope )
				1255	ENDIF
				1256	DROP ( done with that argument )
				1257	;
				1258
				1259	################################################################################
				1260	# The MAIN program just prints a banner and processes its arguments.
Misha Brukman	f39d5d6	2004-05-13 00:24:43 +0000	[diff] [blame]	1261	# STACK<:
Brian Gaeke	9018148	2003-11-24 02:52:51 +0000	[diff] [blame]	1262	# n - number of arguments
				1263	# ... - the arguments
				1264	################################################################################
				1265	: process_arguments
				1266	WHILE ( while there are more arguments )
				1267	do_one_argument ( process one argument )
				1268	END
				1269	;
				1270
				1271	################################################################################
				1272	# The MAIN program just prints a banner and processes its arguments.
Misha Brukman	f39d5d6	2004-05-13 00:24:43 +0000	[diff] [blame]	1273	# STACK<: arguments
Brian Gaeke	9018148	2003-11-24 02:52:51 +0000	[diff] [blame]	1274	################################################################################
				1275	: MAIN
				1276	NIP ( get rid of the program name )
				1277	-- ( reduce number of arguments )
				1278	DUP ( save the arg counter )
Misha Brukman	f39d5d6	2004-05-13 00:24:43 +0000	[diff] [blame]	1279	1 <= IF ( See if we got an argument )
Brian Gaeke	9018148	2003-11-24 02:52:51 +0000	[diff] [blame]	1280	process_arguments ( tell user if they are prime )
				1281	ELSE
				1282	find_primes ( see how many we can find )
				1283	ENDIF
				1284	0 ( push return code )
				1285	;
Brian Gaeke	9018148	2003-11-24 02:52:51 +0000	[diff] [blame]	1286	</code>
Brian Gaeke	07e89e4	2003-11-24 17:03:38 +0000	[diff] [blame]	1287	</pre>
Brian Gaeke	9018148	2003-11-24 02:52:51 +0000	[diff] [blame]	1288	</div>
				1289	<!-- ======================================================================= -->
Brian Gaeke	07e89e4	2003-11-24 17:03:38 +0000	[diff] [blame]	1290	<div class="doc_section"> <a name="internal">Internals</a></div>
				1291	<div class="doc_text">
				1292	<p><b>This section is under construction.</b>
				1293	<p>In the mean time, you can always read the code! It has comments!</p>
				1294	</div>
				1295	<!-- ======================================================================= -->
				1296	<div class="doc_subsection"> <a name="directory">Directory Structure</a></div>
				1297	<div class="doc_text">
				1298	<p>The source code, test programs, and sample programs can all be found
				1299	under the LLVM "projects" directory. You will need to obtain the LLVM sources
				1300	to find it (either via anonymous CVS or a tarball. See the
				1301	<a href="GettingStarted.html">Getting Started</a> document).</p>
John Criswell	d000e1d	2003-12-18 16:43:17 +0000	[diff] [blame]	1302	<p>Under the "projects" directory there is a directory named "Stacker". That
Brian Gaeke	07e89e4	2003-11-24 17:03:38 +0000	[diff] [blame]	1303	directory contains everything, as follows:</p>
				1304	<ul>
				1305	<li><em>lib</em> - contains most of the source code
				1306	<ul>
				1307	<li><em>lib/compiler</em> - contains the compiler library
				1308	<li><em>lib/runtime</em> - contains the runtime library
				1309	</ul></li>
				1310	<li><em>test</em> - contains the test programs</li>
				1311	<li><em>tools</em> - contains the Stacker compiler main program, stkrc
				1312	<ul>
				1313	<li><em>lib/stkrc</em> - contains the Stacker compiler main program
				1314	</ul</li>
				1315	<li><em>sample</em> - contains the sample programs</li>
				1316	</ul>
				1317	</div>
				1318	<!-- ======================================================================= -->
				1319	<div class="doc_subsection"><a name="lexer"></a>The Lexer</div>
				1320	<div class="doc_text">
				1321	<p>See projects/Stacker/lib/compiler/Lexer.l</p>
Misha Brukman	3669299	2004-05-12 19:52:00 +0000	[diff] [blame]	1322	</div>
Brian Gaeke	07e89e4	2003-11-24 17:03:38 +0000	[diff] [blame]	1323	<!-- ======================================================================= -->
				1324	<div class="doc_subsection"><a name="parser"></a>The Parser</div>
				1325	<div class="doc_text">
				1326	<p>See projects/Stacker/lib/compiler/StackerParser.y</p>
Misha Brukman	3669299	2004-05-12 19:52:00 +0000	[diff] [blame]	1327	</div>
Brian Gaeke	07e89e4	2003-11-24 17:03:38 +0000	[diff] [blame]	1328	<!-- ======================================================================= -->
				1329	<div class="doc_subsection"><a name="compiler"></a>The Compiler</div>
				1330	<div class="doc_text">
				1331	<p>See projects/Stacker/lib/compiler/StackerCompiler.cpp</p>
Misha Brukman	3669299	2004-05-12 19:52:00 +0000	[diff] [blame]	1332	</div>
Brian Gaeke	07e89e4	2003-11-24 17:03:38 +0000	[diff] [blame]	1333	<!-- ======================================================================= -->
				1334	<div class="doc_subsection"><a name="runtime"></a>The Runtime</div>
				1335	<div class="doc_text">
				1336	<p>See projects/Stacker/lib/runtime/stacker_rt.c</p>
Misha Brukman	3669299	2004-05-12 19:52:00 +0000	[diff] [blame]	1337	</div>
Brian Gaeke	07e89e4	2003-11-24 17:03:38 +0000	[diff] [blame]	1338	<!-- ======================================================================= -->
				1339	<div class="doc_subsection"><a name="driver"></a>Compiler Driver</div>
				1340	<div class="doc_text">
				1341	<p>See projects/Stacker/tools/stkrc/stkrc.cpp</p>
Misha Brukman	3669299	2004-05-12 19:52:00 +0000	[diff] [blame]	1342	</div>
Brian Gaeke	07e89e4	2003-11-24 17:03:38 +0000	[diff] [blame]	1343	<!-- ======================================================================= -->
				1344	<div class="doc_subsection"><a name="tests"></a>Test Programs</div>
				1345	<div class="doc_text">
				1346	<p>See projects/Stacker/test/*.st</p>
Misha Brukman	3669299	2004-05-12 19:52:00 +0000	[diff] [blame]	1347	</div>
Brian Gaeke	9018148	2003-11-24 02:52:51 +0000	[diff] [blame]	1348	<!-- ======================================================================= -->
Chris Lattner	e46d601	2003-11-25 01:35:06 +0000	[diff] [blame]	1349	<div class="doc_subsection"> <a name="exercise">Exercise</a></div>
				1350	<div class="doc_text">
				1351	<p>As you may have noted from a careful inspection of the Built-In word
				1352	definitions, the ROLL word is not implemented. This word was left out of
				1353	Stacker on purpose so that it can be an exercise for the student. The exercise
				1354	is to implement the ROLL functionality (in your own workspace) and build a test
John Criswell	d000e1d	2003-12-18 16:43:17 +0000	[diff] [blame]	1355	program for it. If you can implement ROLL, you understand Stacker and probably
Chris Lattner	e46d601	2003-11-25 01:35:06 +0000	[diff] [blame]	1356	a fair amount about LLVM since this is one of the more complicated Stacker
				1357	operations. The work will almost be completely limited to the
				1358	<a href="#compiler">compiler</a>.
				1359	<p>The ROLL word is already recognized by both the lexer and parser but ignored
				1360	by the compiler. That means you don't have to futz around with figuring out how
				1361	to get the keyword recognized. It already is. The part of the compiler that
				1362	you need to implement is the <code>ROLL</code> case in the
Misha Brukman	fe22af6	2004-04-16 16:20:07 +0000	[diff] [blame]	1363	<code>StackerCompiler::handle_word(int)</code> method.</p> See the
				1364	implementations of PICK and SELECT in the same method to get some hints about
				1365	how to complete this exercise.<p>
Chris Lattner	e46d601	2003-11-25 01:35:06 +0000	[diff] [blame]	1366	<p>Good luck!</p>
				1367	</div>
				1368	<!-- ======================================================================= -->
Misha Brukman	fe22af6	2004-04-16 16:20:07 +0000	[diff] [blame]	1369	<div class="doc_subsection"><a name="todo">Things Remaining To Be Done</a></div>
Chris Lattner	e46d601	2003-11-25 01:35:06 +0000	[diff] [blame]	1370	<div class="doc_text">
				1371	<p>The initial implementation of Stacker has several deficiencies. If you're
				1372	interested, here are some things that could be implemented better:</p>
				1373	<ol>
				1374	<li>Write an LLVM pass to compute the correct stack depth needed by the
Chris Lattner	45ab10c	2003-12-18 06:40:22 +0000	[diff] [blame]	1375	program. Currently the stack is set to a fixed number which means programs
				1376	with large numbers of definitions might fail.</li>
Chris Lattner	e46d601	2003-11-25 01:35:06 +0000	[diff] [blame]	1377	<li>Write an LLVM pass to optimize the use of the global stack. The code
				1378	emitted currently is somewhat wasteful. It gets cleaned up a lot by existing
				1379	passes but more could be done.</li>
				1380	<li>Add -O -O1 -O2 and -O3 optimization switches to the compiler driver to
John Criswell	d000e1d	2003-12-18 16:43:17 +0000	[diff] [blame]	1381	allow LLVM optimization without using "opt."</li>
Misha Brukman	fe22af6	2004-04-16 16:20:07 +0000	[diff] [blame]	1382	<li>Make the compiler driver use the LLVM linking facilities (with IPO)
				1383	before depending on GCC to do the final link.</li>
Chris Lattner	e46d601	2003-11-25 01:35:06 +0000	[diff] [blame]	1384	<li>Clean up parsing. It doesn't handle errors very well.</li>
				1385	<li>Rearrange the StackerCompiler.cpp code to make better use of inserting
				1386	instructions before a block's terminating instruction. I didn't figure this
Misha Brukman	fe22af6	2004-04-16 16:20:07 +0000	[diff] [blame]	1387	technique out until I was nearly done with LLVM. As it is, its a bad example
Chris Lattner	e46d601	2003-11-25 01:35:06 +0000	[diff] [blame]	1388	of how to insert instructions!</li>
				1389	<li>Provide for I/O to arbitrary files instead of just stdin/stdout.</li>
Chris Lattner	45ab10c	2003-12-18 06:40:22 +0000	[diff] [blame]	1390	<li>Write additional built-in words; with inspiration from FORTH</li>
Chris Lattner	e46d601	2003-11-25 01:35:06 +0000	[diff] [blame]	1391	<li>Write additional sample Stacker programs.</li>
Chris Lattner	45ab10c	2003-12-18 06:40:22 +0000	[diff] [blame]	1392	<li>Add your own compiler writing experiences and tips in the
				1393	<a href="#lessons">Lessons I Learned About LLVM</a> section.</li>
Chris Lattner	e46d601	2003-11-25 01:35:06 +0000	[diff] [blame]	1394	</ol>
				1395	</div>
Misha Brukman	3669299	2004-05-12 19:52:00 +0000	[diff] [blame]	1396
				1397	<!-- *********************************************************************** -->
				1398
Brian Gaeke	9018148	2003-11-24 02:52:51 +0000	[diff] [blame]	1399	<hr>
Misha Brukman	3669299	2004-05-12 19:52:00 +0000	[diff] [blame]	1400	<address>
				1401	<a href="http://jigsaw.w3.org/css-validator/check/referer"><img
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				1405
				1406	<a href="mailto:rspencer@x10sys.com">Reid Spencer</a><br>
				1407	<a href="http://llvm.cs.uiuc.edu">LLVM Compiler Infrastructure</a><br>
				1408	Last modified: $Date$
				1409	</address>
				1410
Brian Gaeke	9018148	2003-11-24 02:52:51 +0000	[diff] [blame]	1411	</body>
				1412	</html>