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diff --git a/docs/Stacker.html b/docs/Stacker.html new file mode 100644 index 0000000..102571a --- /dev/null +++ b/docs/Stacker.html @@ -0,0 +1,1418 @@ +<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN" + "http://www.w3.org/TR/html4/strict.dtd"> +<html> +<head> + <title>Stacker: An Example Of Using LLVM</title> + <link rel="stylesheet" href="llvm.css" type="text/css"> +</head> +<body> + +<div class="doc_title">Stacker: An Example Of Using LLVM</div> + +<ol> + <li><a href="#abstract">Abstract</a></li> + <li><a href="#introduction">Introduction</a></li> + <li><a href="#lessons">Lessons I Learned About LLVM</a> + <ol> + <li><a href="#value">Everything's a Value!</a></li> + <li><a href="#terminate">Terminate Those Blocks!</a></li> + <li><a href="#blocks">Concrete Blocks</a></li> + <li><a href="#push_back">push_back Is Your Friend</a></li> + <li><a href="#gep">The Wily GetElementPtrInst</a></li> + <li><a href="#linkage">Getting Linkage Types Right</a></li> + <li><a href="#constants">Constants Are Easier Than That!</a></li> + </ol></li> + <li><a href="#lexicon">The Stacker Lexicon</a> + <ol> + <li><a href="#stack">The Stack</a></li> + <li><a href="#punctuation">Punctuation</a></li> + <li><a href="#comments">Comments</a></li> + <li><a href="#literals">Literals</a></li> + <li><a href="#words">Words</a></li> + <li><a href="#style">Standard Style</a></li> + <li><a href="#builtins">Built-Ins</a></li> + </ol></li> + <li><a href="#example">Prime: A Complete Example</a></li> + <li><a href="#internal">Internal Code Details</a> + <ol> + <li><a href="#directory">The Directory Structure </a></li> + <li><a href="#lexer">The Lexer</a></li> + <li><a href="#parser">The Parser</a></li> + <li><a href="#compiler">The Compiler</a></li> + <li><a href="#runtime">The Runtime</a></li> + <li><a href="#driver">Compiler Driver</a></li> + <li><a href="#tests">Test Programs</a></li> + <li><a href="#exercise">Exercise</a></li> + <li><a href="#todo">Things Remaining To Be Done</a></li> + </ol></li> +</ol> + +<div class="doc_author"> + <p>Written by <a href="mailto:rspencer@x10sys.com">Reid Spencer</a></p> +</div> + +<!-- ======================================================================= --> +<div class="doc_section"><a name="abstract">Abstract</a></div> +<div class="doc_text"> +<p>This document is another way to learn about LLVM. Unlike the +<a href="LangRef.html">LLVM Reference Manual</a> or +<a href="ProgrammersManual.html">LLVM Programmer's Manual</a>, here we learn +about LLVM through the experience of creating a simple programming language +named Stacker. Stacker was invented specifically as a demonstration of +LLVM. The emphasis in this document is not on describing the +intricacies of LLVM itself but on how to use it to build your own +compiler system.</p> +</div> +<!-- ======================================================================= --> +<div class="doc_section"> <a name="introduction">Introduction</a> </div> +<div class="doc_text"> +<p>Amongst other things, LLVM is a platform for compiler writers. +Because of its exceptionally clean and small IR (intermediate +representation), compiler writing with LLVM is much easier than with +other system. As proof, I wrote the entire compiler (language definition, +lexer, parser, code generator, etc.) in about <em>four days</em>! +That's important to know because it shows how quickly you can get a new +language running when using LLVM. Furthermore, this was the <em >first</em> +language the author ever created using LLVM. The learning curve is +included in that four days.</p> +<p>The language described here, Stacker, is Forth-like. Programs +are simple collections of word definitions, and the only thing definitions +can do is manipulate a stack or generate I/O. Stacker is not a "real" +programming language; it's very simple. Although it is computationally +complete, you wouldn't use it for your next big project. However, +the fact that it is complete, it's simple, and it <em>doesn't</em> have +a C-like syntax make it useful for demonstration purposes. It shows +that LLVM could be applied to a wide variety of languages.</p> +<p>The basic notions behind stacker is very simple. There's a stack of +integers (or character pointers) that the program manipulates. Pretty +much the only thing the program can do is manipulate the stack and do +some limited I/O operations. The language provides you with several +built-in words that manipulate the stack in interesting ways. To get +your feet wet, here's how you write the traditional "Hello, World" +program in Stacker:</p> +<p><code>: hello_world "Hello, World!" >s DROP CR ;<br> +: MAIN hello_world ;<br></code></p> +<p>This has two "definitions" (Stacker manipulates words, not +functions and words have definitions): <code>MAIN</code> and <code> +hello_world</code>. The <code>MAIN</code> definition is standard; it +tells Stacker where to start. Here, <code>MAIN</code> is defined to +simply invoke the word <code>hello_world</code>. The +<code>hello_world</code> definition tells stacker to push the +<code>"Hello, World!"</code> string on to the stack, print it out +(<code>>s</code>), pop it off the stack (<code>DROP</code>), and +finally print a carriage return (<code>CR</code>). Although +<code>hello_world</code> uses the stack, its net effect is null. Well +written Stacker definitions have that characteristic. </p> +<p>Exercise for the reader: how could you make this a one line program?</p> +</div> +<!-- ======================================================================= --> +<div class="doc_section"><a name="lessons"></a>Lessons I Learned About LLVM</div> +<div class="doc_text"> +<p>Stacker was written for two purposes: </p> +<ol> + <li>to get the author over the learning curve, and</li> + <li>to provide a simple example of how to write a compiler using LLVM.</li> +</ol> +<p>During the development of Stacker, many lessons about LLVM were +learned. Those lessons are described in the following subsections.<p> +</div> +<!-- ======================================================================= --> +<div class="doc_subsection"><a name="value"></a>Everything's a Value!</div> +<div class="doc_text"> +<p>Although I knew that LLVM uses a Single Static Assignment (SSA) format, +it wasn't obvious to me how prevalent this idea was in LLVM until I really +started using it. Reading the <a href="ProgrammersManual.html"> +Programmer's Manual</a> and <a href="LangRef.html">Language Reference</a>, +I noted that most of the important LLVM IR (Intermediate Representation) C++ +classes were derived from the Value class. The full power of that simple +design only became fully understood once I started constructing executable +expressions for Stacker.</p> + +<p>This really makes your programming go faster. Think about compiling code +for the following C/C++ expression: <code>(a|b)*((x+1)/(y+1))</code>. Assuming +the values are on the stack in the order a, b, x, y, this could be +expressed in stacker as: <code>1 + SWAP 1 + / ROT2 OR *</code>. +You could write a function using LLVM that computes this expression like +this: </p> + +<div class="doc_code"><pre> +Value* +expression(BasicBlock* bb, Value* a, Value* b, Value* x, Value* y ) +{ + ConstantInt* one = ConstantInt::get(Type::IntTy, 1); + BinaryOperator* or1 = BinaryOperator::createOr(a, b, "", bb); + BinaryOperator* add1 = BinaryOperator::createAdd(x, one, "", bb); + BinaryOperator* add2 = BinaryOperator::createAdd(y, one, "", bb); + BinaryOperator* div1 = BinaryOperator::createDiv(add1, add2, "", bb); + BinaryOperator* mult1 = BinaryOperator::createMul(or1, div1, "", bb); + return mult1; +} +</pre></div> + +<p>"Okay, big deal," you say? It is a big deal. Here's why. Note that I didn't +have to tell this function which kinds of Values are being passed in. They could be +<code>Instruction</code>s, <code>Constant</code>s, <code>GlobalVariable</code>s, or +any of the other subclasses of <code>Value</code> that LLVM supports. +Furthermore, if you specify Values that are incorrect for this sequence of +operations, LLVM will either notice right away (at compilation time) or the LLVM +Verifier will pick up the inconsistency when the compiler runs. In either case +LLVM prevents you from making a type error that gets passed through to the +generated program. This <em>really</em> helps you write a compiler that +always generates correct code!<p> +<p>The second point is that we don't have to worry about branching, registers, +stack variables, saving partial results, etc. The instructions we create +<em>are</em> the values we use. Note that all that was created in the above +code is a Constant value and five operators. Each of the instructions <em>is</em> +the resulting value of that instruction. This saves a lot of time.</p> +<p>The lesson is this: <em>SSA form is very powerful: there is no difference +between a value and the instruction that created it.</em> This is fully +enforced by the LLVM IR. Use it to your best advantage.</p> +</div> +<!-- ======================================================================= --> +<div class="doc_subsection"><a name="terminate"></a>Terminate Those Blocks!</div> +<div class="doc_text"> +<p>I had to learn about terminating blocks the hard way: using the debugger +to figure out what the LLVM verifier was trying to tell me and begging for +help on the LLVMdev mailing list. I hope you avoid this experience.</p> +<p>Emblazon this rule in your mind:</p> +<ul> + <li><em>All</em> <code>BasicBlock</code>s in your compiler <b>must</b> be + terminated with a terminating instruction (branch, return, etc.). + </li> +</ul> +<p>Terminating instructions are a semantic requirement of the LLVM IR. There +is no facility for implicitly chaining together blocks placed into a function +in the order they occur. Indeed, in the general case, blocks will not be +added to the function in the order of execution because of the recursive +way compilers are written.</p> +<p>Furthermore, if you don't terminate your blocks, your compiler code will +compile just fine. You won't find out about the problem until you're running +the compiler and the module you just created fails on the LLVM Verifier.</p> +</div> +<!-- ======================================================================= --> +<div class="doc_subsection"><a name="blocks"></a>Concrete Blocks</div> +<div class="doc_text"> +<p>After a little initial fumbling around, I quickly caught on to how blocks +should be constructed. In general, here's what I learned: +<ol> + <li><em>Create your blocks early.</em> While writing your compiler, you + will encounter several situations where you know apriori that you will + need several blocks. For example, if-then-else, switch, while, and for + statements in C/C++ all need multiple blocks for expression in LLVM. + The rule is, create them early.</li> + <li><em>Terminate your blocks early.</em> This just reduces the chances + that you forget to terminate your blocks which is required (go + <a href="#terminate">here</a> for more). + <li><em>Use getTerminator() for instruction insertion.</em> I noticed early on + that many of the constructors for the Instruction classes take an optional + <code>insert_before</code> argument. At first, I thought this was a mistake + because clearly the normal mode of inserting instructions would be one at + a time <em>after</em> some other instruction, not <em>before</em>. However, + if you hold on to your terminating instruction (or use the handy dandy + <code>getTerminator()</code> method on a <code>BasicBlock</code>), it can + always be used as the <code>insert_before</code> argument to your instruction + constructors. This causes the instruction to automatically be inserted in + the RightPlace™ place, just before the terminating instruction. The + nice thing about this design is that you can pass blocks around and insert + new instructions into them without ever knowing what instructions came + before. This makes for some very clean compiler design.</li> +</ol> +<p>The foregoing is such an important principal, its worth making an idiom:</p> +<pre> +BasicBlock* bb = new BasicBlock(); +bb->getInstList().push_back( new Branch( ... ) ); +new Instruction(..., bb->getTerminator() ); +</pre> +<p>To make this clear, consider the typical if-then-else statement +(see StackerCompiler::handle_if() method). We can set this up +in a single function using LLVM in the following way: </p> +<pre> +using namespace llvm; +BasicBlock* +MyCompiler::handle_if( BasicBlock* bb, ICmpInst* condition ) +{ + // Create the blocks to contain code in the structure of if/then/else + BasicBlock* then_bb = new BasicBlock(); + BasicBlock* else_bb = new BasicBlock(); + BasicBlock* exit_bb = new BasicBlock(); + + // Insert the branch instruction for the "if" + bb->getInstList().push_back( new BranchInst( then_bb, else_bb, condition ) ); + + // Set up the terminating instructions + then->getInstList().push_back( new BranchInst( exit_bb ) ); + else->getInstList().push_back( new BranchInst( exit_bb ) ); + + // Fill in the then part .. details excised for brevity + this->fill_in( then_bb ); + + // Fill in the else part .. details excised for brevity + this->fill_in( else_bb ); + + // Return a block to the caller that can be filled in with the code + // that follows the if/then/else construct. + return exit_bb; +} +</pre> +<p>Presumably in the foregoing, the calls to the "fill_in" method would add +the instructions for the "then" and "else" parts. They would use the third part +of the idiom almost exclusively (inserting new instructions before the +terminator). Furthermore, they could even recurse back to <code>handle_if</code> +should they encounter another if/then/else statement, and it will just work.</p> +<p>Note how cleanly this all works out. In particular, the push_back methods on +the <code>BasicBlock</code>'s instruction list. These are lists of type +<code>Instruction</code> (which is also of type <code>Value</code>). To create +the "if" branch we merely instantiate a <code>BranchInst</code> that takes as +arguments the blocks to branch to and the condition to branch on. The +<code>BasicBlock</code> objects act like branch labels! This new +<code>BranchInst</code> terminates the <code>BasicBlock</code> provided +as an argument. To give the caller a way to keep inserting after calling +<code>handle_if</code>, we create an <code>exit_bb</code> block which is +returned +to the caller. Note that the <code>exit_bb</code> block is used as the +terminator for both the <code>then_bb</code> and the <code>else_bb</code> +blocks. This guarantees that no matter what else <code>handle_if</code> +or <code>fill_in</code> does, they end up at the <code>exit_bb</code> block. +</p> +</div> +<!-- ======================================================================= --> +<div class="doc_subsection"><a name="push_back"></a>push_back Is Your Friend</div> +<div class="doc_text"> +<p> +One of the first things I noticed is the frequent use of the "push_back" +method on the various lists. This is so common that it is worth mentioning. +The "push_back" inserts a value into an STL list, vector, array, etc. at the +end. The method might have also been named "insert_tail" or "append". +Although I've used STL quite frequently, my use of push_back wasn't very +high in other programs. In LLVM, you'll use it all the time. +</p> +</div> +<!-- ======================================================================= --> +<div class="doc_subsection"><a name="gep"></a>The Wily GetElementPtrInst</div> +<div class="doc_text"> +<p> +It took a little getting used to and several rounds of postings to the LLVM +mailing list to wrap my head around this instruction correctly. Even though I had +read the Language Reference and Programmer's Manual a couple times each, I still +missed a few <em>very</em> key points: +</p> +<ul> +<li>GetElementPtrInst gives you back a Value for the last thing indexed.</li> +<li>All global variables in LLVM are <em>pointers</em>.</li> +<li>Pointers must also be dereferenced with the GetElementPtrInst +instruction.</li> +</ul> +<p>This means that when you look up an element in the global variable (assuming +it's a struct or array), you <em>must</em> deference the pointer first! For many +things, this leads to the idiom: +</p> +<pre> +std::vector<Value*> index_vector; +index_vector.push_back( ConstantInt::get( Type::LongTy, 0 ); +// ... push other indices ... +GetElementPtrInst* gep = new GetElementPtrInst( ptr, index_vector ); +</pre> +<p>For example, suppose we have a global variable whose type is [24 x int]. The +variable itself represents a <em>pointer</em> to that array. To subscript the +array, we need two indices, not just one. The first index (0) dereferences the +pointer. The second index subscripts the array. If you're a "C" programmer, this +will run against your grain because you'll naturally think of the global array +variable and the address of its first element as the same. That tripped me up +for a while until I realized that they really do differ .. by <em>type</em>. +Remember that LLVM is strongly typed. Everything has a type. +The "type" of the global variable is [24 x int]*. That is, it's +a pointer to an array of 24 ints. When you dereference that global variable with +a single (0) index, you now have a "[24 x int]" type. Although +the pointer value of the dereferenced global and the address of the zero'th element +in the array will be the same, they differ in their type. The zero'th element has +type "int" while the pointer value has type "[24 x int]".</p> +<p>Get this one aspect of LLVM right in your head, and you'll save yourself +a lot of compiler writing headaches down the road.</p> +</div> +<!-- ======================================================================= --> +<div class="doc_subsection"><a name="linkage"></a>Getting Linkage Types Right</div> +<div class="doc_text"> +<p>Linkage types in LLVM can be a little confusing, especially if your compiler +writing mind has affixed firm concepts to particular words like "weak", +"external", "global", "linkonce", etc. LLVM does <em>not</em> use the precise +definitions of, say, ELF or GCC, even though they share common terms. To be fair, +the concepts are related and similar but not precisely the same. This can lead +you to think you know what a linkage type represents but in fact it is slightly +different. I recommend you read the +<a href="LangRef.html#linkage"> Language Reference on this topic</a> very +carefully. Then, read it again.<p> +<p>Here are some handy tips that I discovered along the way:</p> +<ul> + <li><em>Uninitialized means external.</em> That is, the symbol is declared in the current + module and can be used by that module, but it is not defined by that module.</li> + <li><em>Setting an initializer changes a global' linkage type.</em> Setting an + initializer changes a global's linkage type from whatever it was to a normal, + defined global (not external). You'll need to call the setLinkage() method to + reset it if you specify the initializer after the GlobalValue has been constructed. + This is important for LinkOnce and Weak linkage types.</li> + <li><em>Appending linkage can keep track of things.</em> Appending linkage can + be used to keep track of compilation information at runtime. It could be used, + for example, to build a full table of all the C++ virtual tables or hold the + C++ RTTI data, or whatever. Appending linkage can only be applied to arrays. + All arrays with the same name in each module are concatenated together at link + time.</li> +</ul> +</div> +<!-- ======================================================================= --> +<div class="doc_subsection"><a name="constants"></a>Constants Are Easier Than That!</div> +<div class="doc_text"> +<p> +Constants in LLVM took a little getting used to until I discovered a few utility +functions in the LLVM IR that make things easier. Here's what I learned: </p> +<ul> + <li>Constants are Values like anything else and can be operands of instructions</li> + <li>Integer constants, frequently needed, can be created using the static "get" + methods of the ConstantInt class. The nice thing about these is that you can + "get" any kind of integer quickly.</li> + <li>There's a special method on Constant class which allows you to get the null + constant for <em>any</em> type. This is really handy for initializing large + arrays or structures, etc.</li> +</ul> +</div> +<!-- ======================================================================= --> +<div class="doc_section"> <a name="lexicon">The Stacker Lexicon</a></div> +<div class="doc_text"><p>This section describes the Stacker language</p></div> +<div class="doc_subsection"><a name="stack"></a>The Stack</div> +<div class="doc_text"> +<p>Stacker definitions define what they do to the global stack. Before +proceeding, a few words about the stack are in order. The stack is simply +a global array of 32-bit integers or pointers. A global index keeps track +of the location of the top of the stack. All of this is hidden from the +programmer, but it needs to be noted because it is the foundation of the +conceptual programming model for Stacker. When you write a definition, +you are, essentially, saying how you want that definition to manipulate +the global stack.</p> +<p>Manipulating the stack can be quite hazardous. There is no distinction +given and no checking for the various types of values that can be placed +on the stack. Automatic coercion between types is performed. In many +cases, this is useful. For example, a boolean value placed on the stack +can be interpreted as an integer with good results. However, using a +word that interprets that boolean value as a pointer to a string to +print out will almost always yield a crash. Stacker simply leaves it +to the programmer to get it right without any interference or hindering +on interpretation of the stack values. You've been warned. :) </p> +</div> +<!-- ======================================================================= --> +<div class="doc_subsection"> <a name="punctuation"></a>Punctuation</div> +<div class="doc_text"> +<p>Punctuation in Stacker is very simple. The colon and semi-colon +characters are used to introduce and terminate a definition +(respectively). Except for <em>FORWARD</em> declarations, definitions +are all you can specify in Stacker. Definitions are read left to right. +Immediately after the colon comes the name of the word being defined. +The remaining words in the definition specify what the word does. The definition +is terminated by a semi-colon.</p> +<p>So, your typical definition will have the form:</p> +<pre><code>: name ... ;</code></pre> +<p>The <code>name</code> is up to you but it must start with a letter and contain +only letters, numbers, and underscore. Names are case sensitive and must not be +the same as the name of a built-in word. The <code>...</code> is replaced by +the stack manipulating words that you wish to define <code>name</code> as. <p> +</div> +<!-- ======================================================================= --> +<div class="doc_subsection"><a name="comments"></a>Comments</div> +<div class="doc_text"> + <p>Stacker supports two types of comments. A hash mark (#) starts a comment + that extends to the end of the line. It is identical to the kind of comments + commonly used in shell scripts. A pair of parentheses also surround a comment. + In both cases, the content of the comment is ignored by the Stacker compiler. The + following does nothing in Stacker. + </p> +<pre><code> +# This is a comment to end of line +( This is an enclosed comment ) +</code></pre> +<p>See the <a href="#example">example</a> program to see comments in use in +a real program.</p> +</div> +<!-- ======================================================================= --> +<div class="doc_subsection"><a name="literals"></a>Literals</div> +<div class="doc_text"> + <p>There are three kinds of literal values in Stacker: Integers, Strings, + and Booleans. In each case, the stack operation is to simply push the + value on to the stack. So, for example:<br/> + <code> 42 " is the answer." TRUE </code><br/> + will push three values on to the stack: the integer 42, the + string " is the answer.", and the boolean TRUE.</p> +</div> +<!-- ======================================================================= --> +<div class="doc_subsection"><a name="words"></a>Words</div> +<div class="doc_text"> +<p>Each definition in Stacker is composed of a set of words. Words are +read and executed in order from left to right. There is very little +checking in Stacker to make sure you're doing the right thing with +the stack. It is assumed that the programmer knows how the stack +transformation he applies will affect the program.</p> +<p>Words in a definition come in two flavors: built-in and programmer +defined. Simply mentioning the name of a previously defined or declared +programmer-defined word causes that word's stack actions to be invoked. It +is somewhat like a function call in other languages. The built-in +words have various effects, described <a href="#builtins">below</a>.</p> +<p>Sometimes you need to call a word before it is defined. For this, you can +use the <code>FORWARD</code> declaration. It looks like this:</p> +<p><code>FORWARD name ;</code></p> +<p>This simply states to Stacker that "name" is the name of a definition +that is defined elsewhere. Generally it means the definition can be found +"forward" in the file. But, it doesn't have to be in the current compilation +unit. Anything declared with <code>FORWARD</code> is an external symbol for +linking.</p> +</div> +<!-- ======================================================================= --> +<div class="doc_subsection"><a name="style"></a>Standard Style</div> +<div class="doc_text"> +<p>TODO</p> +</div> +<!-- ======================================================================= --> +<div class="doc_subsection"><a name="builtins"></a>Built In Words</div> +<div class="doc_text"> +<p>The built-in words of the Stacker language are put in several groups +depending on what they do. The groups are as follows:</p> +<ol> + <li><em>Logical</em>: These words provide the logical operations for + comparing stack operands.<br/>The words are: < > <= >= + = <> true false.</li> + <li><em>Bitwise</em>: These words perform bitwise computations on + their operands. <br/> The words are: << >> XOR AND NOT</li> + <li><em>Arithmetic</em>: These words perform arithmetic computations on + their operands. <br/> The words are: ABS NEG + - * / MOD */ ++ -- MIN MAX</li> + <li><em>Stack</em>These words manipulate the stack directly by moving + its elements around.<br/> The words are: DROP DROP2 NIP NIP2 DUP DUP2 + SWAP SWAP2 OVER OVER2 ROT ROT2 RROT RROT2 TUCK TUCK2 PICK SELECT ROLL</li> + <li><em>Memory</em>These words allocate, free, and manipulate memory + areas outside the stack.<br/>The words are: MALLOC FREE GET PUT</li> + <li><em>Control</em>: These words alter the normal left to right flow + of execution.<br/>The words are: IF ELSE ENDIF WHILE END RETURN EXIT RECURSE</li> + <li><em>I/O</em>: These words perform output on the standard output + and input on the standard input. No other I/O is possible in Stacker. + <br/>The words are: SPACE TAB CR >s >d >c <s <d <c.</li> +</ol> +<p>While you may be familiar with many of these operations from other +programming languages, a careful review of their semantics is important +for correct programming in Stacker. Of most importance is the effect +that each of these built-in words has on the global stack. The effect is +not always intuitive. To better describe the effects, we'll borrow from Forth the idiom of +describing the effect on the stack with:</p> +<p><code> BEFORE -- AFTER </code></p> +<p>That is, to the left of the -- is a representation of the stack before +the operation. To the right of the -- is a representation of the stack +after the operation. In the table below that describes the operation of +each of the built in words, we will denote the elements of the stack +using the following construction:</p> +<ol> + <li><em>b</em> - a boolean truth value</li> + <li><em>w</em> - a normal integer valued word.</li> + <li><em>s</em> - a pointer to a string value</li> + <li><em>p</em> - a pointer to a malloc'd memory block</li> +</ol> +</div> +<div class="doc_text" > + <table> +<tr><th colspan="4">Definition Of Operation Of Built In Words</th></tr> +<tr><th colspan="4"><b>LOGICAL OPERATIONS</b></th></tr> +<tr> + <td>Word</td> + <td>Name</td> + <td>Operation</td> + <td>Description</td> +</tr> +<tr> + <td><</td> + <td>LT</td> + <td>w1 w2 -- b</td> + <td>Two values (w1 and w2) are popped off the stack and + compared. If w1 is less than w2, TRUE is pushed back on + the stack, otherwise FALSE is pushed back on the stack.</td> +</tr> +<tr><td>></td> + <td>GT</td> + <td>w1 w2 -- b</td> + <td>Two values (w1 and w2) are popped off the stack and + compared. If w1 is greater than w2, TRUE is pushed back on + the stack, otherwise FALSE is pushed back on the stack.</td> +</tr> +<tr><td>>=</td> + <td>GE</td> + <td>w1 w2 -- b</td> + <td>Two values (w1 and w2) are popped off the stack and + compared. If w1 is greater than or equal to w2, TRUE is + pushed back on the stack, otherwise FALSE is pushed back + on the stack.</td> +</tr> +<tr><td><=</td> + <td>LE</td> + <td>w1 w2 -- b</td> + <td>Two values (w1 and w2) are popped off the stack and + compared. If w1 is less than or equal to w2, TRUE is + pushed back on the stack, otherwise FALSE is pushed back + on the stack.</td> +</tr> +<tr><td>=</td> + <td>EQ</td> + <td>w1 w2 -- b</td> + <td>Two values (w1 and w2) are popped off the stack and + compared. If w1 is equal to w2, TRUE is + pushed back on the stack, otherwise FALSE is pushed back + </td> +</tr> +<tr><td><></td> + <td>NE</td> + <td>w1 w2 -- b</td> + <td>Two values (w1 and w2) are popped off the stack and + compared. If w1 is equal to w2, TRUE is + pushed back on the stack, otherwise FALSE is pushed back + </td> +</tr> +<tr><td>FALSE</td> + <td>FALSE</td> + <td> -- b</td> + <td>The boolean value FALSE (0) is pushed on to the stack.</td> +</tr> +<tr><td>TRUE</td> + <td>TRUE</td> + <td> -- b</td> + <td>The boolean value TRUE (-1) is pushed on to the stack.</td> +</tr> +<tr><th colspan="4"><b>BITWISE OPERATORS</b></th></tr> +<tr> + <td>Word</td> + <td>Name</td> + <td>Operation</td> + <td>Description</td> +</tr> +<tr><td><<</td> + <td>SHL</td> + <td>w1 w2 -- w1<<w2</td> + <td>Two values (w1 and w2) are popped off the stack. The w2 + operand is shifted left by the number of bits given by the + w1 operand. The result is pushed back to the stack.</td> +</tr> +<tr><td>>></td> + <td>SHR</td> + <td>w1 w2 -- w1>>w2</td> + <td>Two values (w1 and w2) are popped off the stack. The w2 + operand is shifted right by the number of bits given by the + w1 operand. The result is pushed back to the stack.</td> +</tr> +<tr><td>OR</td> + <td>OR</td> + <td>w1 w2 -- w2|w1</td> + <td>Two values (w1 and w2) are popped off the stack. The values + are bitwise OR'd together and pushed back on the stack. This is + not a logical OR. The sequence 1 2 OR yields 3 not 1.</td> +</tr> +<tr><td>AND</td> + <td>AND</td> + <td>w1 w2 -- w2&w1</td> + <td>Two values (w1 and w2) are popped off the stack. The values + are bitwise AND'd together and pushed back on the stack. This is + not a logical AND. The sequence 1 2 AND yields 0 not 1.</td> +</tr> +<tr><td>XOR</td> + <td>XOR</td> + <td>w1 w2 -- w2^w1</td> + <td>Two values (w1 and w2) are popped off the stack. The values + are bitwise exclusive OR'd together and pushed back on the stack. + For example, The sequence 1 3 XOR yields 2.</td> +</tr> +<tr><th colspan="4"><b>ARITHMETIC OPERATORS</b></th></tr> +<tr> + <td>Word</td> + <td>Name</td> + <td>Operation</td> + <td>Description</td> +</tr> +<tr><td>ABS</td> + <td>ABS</td> + <td>w -- |w|</td> + <td>One value s popped off the stack; its absolute value is computed + and then pushed on to the stack. If w1 is -1 then w2 is 1. If w1 is + 1 then w2 is also 1.</td> +</tr> +<tr><td>NEG</td> + <td>NEG</td> + <td>w -- -w</td> + <td>One value is popped off the stack which is negated and then + pushed back on to the stack. If w1 is -1 then w2 is 1. If w1 is + 1 then w2 is -1.</td> +</tr> +<tr><td> + </td> + <td>ADD</td> + <td>w1 w2 -- w2+w1</td> + <td>Two values are popped off the stack. Their sum is pushed back + on to the stack</td> +</tr> +<tr><td> - </td> + <td>SUB</td> + <td>w1 w2 -- w2-w1</td> + <td>Two values are popped off the stack. Their difference is pushed back + on to the stack</td> +</tr> +<tr><td> * </td> + <td>MUL</td> + <td>w1 w2 -- w2*w1</td> + <td>Two values are popped off the stack. Their product is pushed back + on to the stack</td> +</tr> +<tr><td> / </td> + <td>DIV</td> + <td>w1 w2 -- w2/w1</td> + <td>Two values are popped off the stack. Their quotient is pushed back + on to the stack</td> +</tr> +<tr><td>MOD</td> + <td>MOD</td> + <td>w1 w2 -- w2%w1</td> + <td>Two values are popped off the stack. Their remainder after division + of w1 by w2 is pushed back on to the stack</td> +</tr> +<tr><td> */ </td> + <td>STAR_SLAH</td> + <td>w1 w2 w3 -- (w3*w2)/w1</td> + <td>Three values are popped off the stack. The product of w1 and w2 is + divided by w3. The result is pushed back on to the stack.</td> +</tr> +<tr><td> ++ </td> + <td>INCR</td> + <td>w -- w+1</td> + <td>One value is popped off the stack. It is incremented by one and then + pushed back on to the stack.</td> +</tr> +<tr><td> -- </td> + <td>DECR</td> + <td>w -- w-1</td> + <td>One value is popped off the stack. It is decremented by one and then + pushed back on to the stack.</td> +</tr> +<tr><td>MIN</td> + <td>MIN</td> + <td>w1 w2 -- (w2<w1?w2:w1)</td> + <td>Two values are popped off the stack. The larger one is pushed back + on to the stack.</td> +</tr> +<tr><td>MAX</td> + <td>MAX</td> + <td>w1 w2 -- (w2>w1?w2:w1)</td> + <td>Two values are popped off the stack. The larger value is pushed back + on to the stack.</td> +</tr> +<tr><th colspan="4"><b>STACK MANIPULATION OPERATORS</b></th></tr> +<tr> + <td>Word</td> + <td>Name</td> + <td>Operation</td> + <td>Description</td> +</tr> +<tr><td>DROP</td> + <td>DROP</td> + <td>w -- </td> + <td>One value is popped off the stack.</td> +</tr> +<tr><td>DROP2</td> + <td>DROP2</td> + <td>w1 w2 -- </td> + <td>Two values are popped off the stack.</td> +</tr> +<tr><td>NIP</td> + <td>NIP</td> + <td>w1 w2 -- w2</td> + <td>The second value on the stack is removed from the stack. That is, + a value is popped off the stack and retained. Then a second value is + popped and the retained value is pushed.</td> +</tr> +<tr><td>NIP2</td> + <td>NIP2</td> + <td>w1 w2 w3 w4 -- w3 w4</td> + <td>The third and fourth values on the stack are removed from it. That is, + two values are popped and retained. Then two more values are popped and + the two retained values are pushed back on.</td> +</tr> +<tr><td>DUP</td> + <td>DUP</td> + <td>w1 -- w1 w1</td> + <td>One value is popped off the stack. That value is then pushed on to + the stack twice to duplicate the top stack vaue.</td> +</tr> +<tr><td>DUP2</td> + <td>DUP2</td> + <td>w1 w2 -- w1 w2 w1 w2</td> + <td>The top two values on the stack are duplicated. That is, two vaues + are popped off the stack. They are alternately pushed back on the + stack twice each.</td> +</tr> +<tr><td>SWAP</td> + <td>SWAP</td> + <td>w1 w2 -- w2 w1</td> + <td>The top two stack items are reversed in their order. That is, two + values are popped off the stack and pushed back on to the stack in + the opposite order they were popped.</td> +</tr> +<tr><td>SWAP2</td> + <td>SWAP2</td> + <td>w1 w2 w3 w4 -- w3 w4 w2 w1</td> + <td>The top four stack items are swapped in pairs. That is, two values + are popped and retained. Then, two more values are popped and retained. + The values are pushed back on to the stack in the reverse order but + in pairs.</td> +</tr> +<tr><td>OVER</td> + <td>OVER</td> + <td>w1 w2-- w1 w2 w1</td> + <td>Two values are popped from the stack. They are pushed back + on to the stack in the order w1 w2 w1. This seems to cause the + top stack element to be duplicated "over" the next value.</td> +</tr> +<tr><td>OVER2</td> + <td>OVER2</td> + <td>w1 w2 w3 w4 -- w1 w2 w3 w4 w1 w2</td> + <td>The third and fourth values on the stack are replicated on to the + top of the stack</td> +</tr> +<tr><td>ROT</td> + <td>ROT</td> + <td>w1 w2 w3 -- w2 w3 w1</td> + <td>The top three values are rotated. That is, three value are popped + off the stack. They are pushed back on to the stack in the order + w1 w3 w2.</td> +</tr> +<tr><td>ROT2</td> + <td>ROT2</td> + <td>w1 w2 w3 w4 w5 w6 -- w3 w4 w5 w6 w1 w2</td> + <td>Like ROT but the rotation is done using three pairs instead of + three singles.</td> +</tr> +<tr><td>RROT</td> + <td>RROT</td> + <td>w1 w2 w3 -- w3 w1 w2</td> + <td>Reverse rotation. Like ROT, but it rotates the other way around. + Essentially, the third element on the stack is moved to the top + of the stack.</td> +</tr> +<tr><td>RROT2</td> + <td>RROT2</td> + <td>w1 w2 w3 w4 w5 w6 -- w3 w4 w5 w6 w1 w2</td> + <td>Double reverse rotation. Like RROT but the rotation is done using + three pairs instead of three singles. The fifth and sixth stack + elements are moved to the first and second positions</td> +</tr> +<tr><td>TUCK</td> + <td>TUCK</td> + <td>w1 w2 -- w2 w1 w2</td> + <td>Similar to OVER except that the second operand is being + replicated. Essentially, the first operand is being "tucked" + in between two instances of the second operand. Logically, two + values are popped off the stack. They are placed back on the + stack in the order w2 w1 w2.</td> +</tr> +<tr><td>TUCK2</td> + <td>TUCK2</td> + <td>w1 w2 w3 w4 -- w3 w4 w1 w2 w3 w4</td> + <td>Like TUCK but a pair of elements is tucked over two pairs. + That is, the top two elements of the stack are duplicated and + inserted into the stack at the fifth and positions.</td> +</tr> +<tr><td>PICK</td> + <td>PICK</td> + <td>x0 ... Xn n -- x0 ... Xn x0</td> + <td>The top of the stack is used as an index into the remainder of + the stack. The element at the nth position replaces the index + (top of stack). This is useful for cycling through a set of + values. Note that indexing is zero based. So, if n=0 then you + get the second item on the stack. If n=1 you get the third, etc. + Note also that the index is replaced by the n'th value. </td> +</tr> +<tr><td>SELECT</td> + <td>SELECT</td> + <td>m n X0..Xm Xm+1 .. Xn -- Xm</td> + <td>This is like PICK but the list is removed and you need to specify + both the index and the size of the list. Careful with this one, + the wrong value for n can blow away a huge amount of the stack.</td> +</tr> +<tr><td>ROLL</td> + <td>ROLL</td> + <td>x0 x1 .. xn n -- x1 .. xn x0</td> + <td><b>Not Implemented</b>. This one has been left as an exercise to + the student. See <a href="#exercise">Exercise</a>. ROLL requires + a value, "n", to be on the top of the stack. This value specifies how + far into the stack to "roll". The n'th value is <em>moved</em> (not + copied) from its location and replaces the "n" value on the top of the + stack. In this way, all the values between "n" and x0 roll up the stack. + The operation of ROLL is a generalized ROT. The "n" value specifies + how much to rotate. That is, ROLL with n=1 is the same as ROT and + ROLL with n=2 is the same as ROT2.</td> +</tr> +<tr><th colspan="4"><b>MEMORY OPERATORS</b></th></tr> +<tr> + <td>Word</td> + <td>Name</td> + <td>Operation</td> + <td>Description</td> +</tr> +<tr><td>MALLOC</td> + <td>MALLOC</td> + <td>w1 -- p</td> + <td>One value is popped off the stack. The value is used as the size + of a memory block to allocate. The size is in bytes, not words. + The memory allocation is completed and the address of the memory + block is pushed on to the stack.</td> +</tr> +<tr><td>FREE</td> + <td>FREE</td> + <td>p -- </td> + <td>One pointer value is popped off the stack. The value should be + the address of a memory block created by the MALLOC operation. The + associated memory block is freed. Nothing is pushed back on the + stack. Many bugs can be created by attempting to FREE something + that isn't a pointer to a MALLOC allocated memory block. Make + sure you know what's on the stack. One way to do this is with + the following idiom:<br/> + <code>64 MALLOC DUP DUP (use ptr) DUP (use ptr) ... FREE</code> + <br/>This ensures that an extra copy of the pointer is placed on + the stack (for the FREE at the end) and that every use of the + pointer is preceded by a DUP to retain the copy for FREE.</td> +</tr> +<tr><td>GET</td> + <td>GET</td> + <td>w1 p -- w2 p</td> + <td>An integer index and a pointer to a memory block are popped of + the block. The index is used to index one byte from the memory + block. That byte value is retained, the pointer is pushed again + and the retained value is pushed. Note that the pointer value + s essentially retained in its position so this doesn't count + as a "use ptr" in the FREE idiom.</td> +</tr> +<tr><td>PUT</td> + <td>PUT</td> + <td>w1 w2 p -- p </td> + <td>An integer value is popped of the stack. This is the value to + be put into a memory block. Another integer value is popped of + the stack. This is the indexed byte in the memory block. A + pointer to the memory block is popped off the stack. The + first value (w1) is then converted to a byte and written + to the element of the memory block(p) at the index given + by the second value (w2). The pointer to the memory block is + pushed back on the stack so this doesn't count as a "use ptr" + in the FREE idiom.</td> +</tr> +<tr><th colspan="4"><b>CONTROL FLOW OPERATORS</b></th></tr> +<tr> + <td>Word</td> + <td>Name</td> + <td>Operation</td> + <td>Description</td> +</tr> +<tr><td>RETURN</td> + <td>RETURN</td> + <td> -- </td> + <td>The currently executing definition returns immediately to its caller. + Note that there is an implicit <code>RETURN</code> at the end of each + definition, logically located at the semi-colon. The sequence + <code>RETURN ;</code> is valid but redundant.</td> +</tr> +<tr><td>EXIT</td> + <td>EXIT</td> + <td>w1 -- </td> + <td>A return value for the program is popped off the stack. The program is + then immediately terminated. This is normally an abnormal exit from the + program. For a normal exit (when <code>MAIN</code> finishes), the exit + code will always be zero in accordance with UNIX conventions.</td> +</tr> +<tr><td>RECURSE</td> + <td>RECURSE</td> + <td> -- </td> + <td>The currently executed definition is called again. This operation is + needed since the definition of a word doesn't exist until the semi colon + is reacher. Attempting something like:<br/> + <code> : recurser recurser ; </code><br/> will yield and error saying that + "recurser" is not defined yet. To accomplish the same thing, change this + to:<br/> + <code> : recurser RECURSE ; </code></td> +</tr> +<tr><td>IF (words...) ENDIF</td> + <td>IF (words...) ENDIF</td> + <td>b -- </td> + <td>A boolean value is popped of the stack. If it is non-zero then the "words..." + are executed. Otherwise, execution continues immediately following the ENDIF.</td> +</tr> +<tr><td>IF (words...) ELSE (words...) ENDIF</td> + <td>IF (words...) ELSE (words...) ENDIF</td> + <td>b -- </td> + <td>A boolean value is popped of the stack. If it is non-zero then the "words..." + between IF and ELSE are executed. Otherwise the words between ELSE and ENDIF are + executed. In either case, after the (words....) have executed, execution continues + immediately following the ENDIF. </td> +</tr> +<tr><td>WHILE word END</td> + <td>WHILE word END</td> + <td>b -- b </td> + <td>The boolean value on the top of the stack is examined (not popped). If + it is non-zero then the "word" between WHILE and END is executed. + Execution then begins again at the WHILE where the boolean on the top of + the stack is examined again. The stack is not modified by the WHILE...END + loop, only examined. It is imperative that the "word" in the body of the + loop ensure that the top of the stack contains the next boolean to examine + when it completes. Note that since booleans and integers can be coerced + you can use the following "for loop" idiom:<br/> + <code>(push count) WHILE word -- END</code><br/> + For example:<br/> + <code>10 WHILE >d -- END</code><br/> + This will print the numbers from 10 down to 1. 10 is pushed on the + stack. Since that is non-zero, the while loop is entered. The top of + the stack (10) is printed out with >d. The top of the stack is + decremented, yielding 9 and control is transfered back to the WHILE + keyword. The process starts all over again and repeats until + the top of stack is decremented to 0 at which point the WHILE test + fails and control is transfered to the word after the END. + </td> +</tr> +<tr><th colspan="4"><b>INPUT & OUTPUT OPERATORS</b></th></tr> +<tr> + <td>Word</td> + <td>Name</td> + <td>Operation</td> + <td>Description</td> +</tr> +<tr><td>SPACE</td> + <td>SPACE</td> + <td> -- </td> + <td>A space character is put out. There is no stack effect.</td> +</tr> +<tr><td>TAB</td> + <td>TAB</td> + <td> -- </td> + <td>A tab character is put out. There is no stack effect.</td> +</tr> +<tr><td>CR</td> + <td>CR</td> + <td> -- </td> + <td>A carriage return character is put out. There is no stack effect.</td> +</tr> +<tr><td>>s</td> + <td>OUT_STR</td> + <td> -- </td> + <td>A string pointer is popped from the stack. It is put out.</td> +</tr> +<tr><td>>d</td> + <td>OUT_STR</td> + <td> -- </td> + <td>A value is popped from the stack. It is put out as a decimal + integer.</td> +</tr> +<tr><td>>c</td> + <td>OUT_CHR</td> + <td> -- </td> + <td>A value is popped from the stack. It is put out as an ASCII + character.</td> +</tr> +<tr><td><s</td> + <td>IN_STR</td> + <td> -- s </td> + <td>A string is read from the input via the scanf(3) format string " %as". + The resulting string is pushed on to the stack.</td> +</tr> +<tr><td><d</td> + <td>IN_STR</td> + <td> -- w </td> + <td>An integer is read from the input via the scanf(3) format string " %d". + The resulting value is pushed on to the stack</td> +</tr> +<tr><td><c</td> + <td>IN_CHR</td> + <td> -- w </td> + <td>A single character is read from the input via the scanf(3) format string + " %c". The value is converted to an integer and pushed on to the stack.</td> +</tr> +<tr><td>DUMP</td> + <td>DUMP</td> + <td> -- </td> + <td>The stack contents are dumped to standard output. This is useful for + debugging your definitions. Put DUMP at the beginning and end of a definition + to see instantly the net effect of the definition.</td> +</tr> +</table> + +</div> +<!-- ======================================================================= --> +<div class="doc_section"> <a name="example">Prime: A Complete Example</a></div> +<div class="doc_text"> +<p>The following fully documented program highlights many features of both +the Stacker language and what is possible with LLVM. The program has two modes +of operation. If you provide numeric arguments to the program, it checks to see +if those arguments are prime numbers and prints out the results. Without any +arguments, the program prints out any prime numbers it finds between 1 and one +million (there's a lot of them!). The source code comments below tell the +remainder of the story. +</p> +</div> +<div class="doc_text"> +<pre><code> +################################################################################ +# +# Brute force prime number generator +# +# This program is written in classic Stacker style, that being the style of a +# stack. Start at the bottom and read your way up ! +# +# Reid Spencer - Nov 2003 +################################################################################ +# Utility definitions +################################################################################ +: print >d CR ; +: it_is_a_prime TRUE ; +: it_is_not_a_prime FALSE ; +: continue_loop TRUE ; +: exit_loop FALSE; + +################################################################################ +# This definition tries an actual division of a candidate prime number. It +# determines whether the division loop on this candidate should continue or +# not. +# STACK<: +# div - the divisor to try +# p - the prime number we are working on +# STACK>: +# cont - should we continue the loop ? +# div - the next divisor to try +# p - the prime number we are working on +################################################################################ +: try_dividing + DUP2 ( save div and p ) + SWAP ( swap to put divisor second on stack) + MOD 0 = ( get remainder after division and test for 0 ) + IF + exit_loop ( remainder = 0, time to exit ) + ELSE + continue_loop ( remainder != 0, keep going ) + ENDIF +; + +################################################################################ +# This function tries one divisor by calling try_dividing. But, before doing +# that it checks to see if the value is 1. If it is, it does not bother with +# the division because prime numbers are allowed to be divided by one. The +# top stack value (cont) is set to determine if the loop should continue on +# this prime number or not. +# STACK<: +# cont - should we continue the loop (ignored)? +# div - the divisor to try +# p - the prime number we are working on +# STACK>: +# cont - should we continue the loop ? +# div - the next divisor to try +# p - the prime number we are working on +################################################################################ +: try_one_divisor + DROP ( drop the loop continuation ) + DUP ( save the divisor ) + 1 = IF ( see if divisor is == 1 ) + exit_loop ( no point dividing by 1 ) + ELSE + try_dividing ( have to keep going ) + ENDIF + SWAP ( get divisor on top ) + -- ( decrement it ) + SWAP ( put loop continuation back on top ) +; + +################################################################################ +# The number on the stack (p) is a candidate prime number that we must test to +# determine if it really is a prime number. To do this, we divide it by every +# number from one p-1 to 1. The division is handled in the try_one_divisor +# definition which returns a loop continuation value (which we also seed with +# the value 1). After the loop, we check the divisor. If it decremented all +# the way to zero then we found a prime, otherwise we did not find one. +# STACK<: +# p - the prime number to check +# STACK>: +# yn - boolean indicating if its a prime or not +# p - the prime number checked +################################################################################ +: try_harder + DUP ( duplicate to get divisor value ) ) + -- ( first divisor is one less than p ) + 1 ( continue the loop ) + WHILE + try_one_divisor ( see if its prime ) + END + DROP ( drop the continuation value ) + 0 = IF ( test for divisor == 1 ) + it_is_a_prime ( we found one ) + ELSE + it_is_not_a_prime ( nope, this one is not a prime ) + ENDIF +; + +################################################################################ +# This definition determines if the number on the top of the stack is a prime +# or not. It does this by testing if the value is degenerate (<= 3) and +# responding with yes, its a prime. Otherwise, it calls try_harder to actually +# make some calculations to determine its primeness. +# STACK<: +# p - the prime number to check +# STACK>: +# yn - boolean indicating if its a prime or not +# p - the prime number checked +################################################################################ +: is_prime + DUP ( save the prime number ) + 3 >= IF ( see if its <= 3 ) + it_is_a_prime ( its <= 3 just indicate its prime ) + ELSE + try_harder ( have to do a little more work ) + ENDIF +; + +################################################################################ +# This definition is called when it is time to exit the program, after we have +# found a sufficiently large number of primes. +# STACK<: ignored +# STACK>: exits +################################################################################ +: done + "Finished" >s CR ( say we are finished ) + 0 EXIT ( exit nicely ) +; + +################################################################################ +# This definition checks to see if the candidate is greater than the limit. If +# it is, it terminates the program by calling done. Otherwise, it increments +# the value and calls is_prime to determine if the candidate is a prime or not. +# If it is a prime, it prints it. Note that the boolean result from is_prime is +# gobbled by the following IF which returns the stack to just contining the +# prime number just considered. +# STACK<: +# p - one less than the prime number to consider +# STAC>K +# p+1 - the prime number considered +################################################################################ +: consider_prime + DUP ( save the prime number to consider ) + 1000000 < IF ( check to see if we are done yet ) + done ( we are done, call "done" ) + ENDIF + ++ ( increment to next prime number ) + is_prime ( see if it is a prime ) + IF + print ( it is, print it ) + ENDIF +; + +################################################################################ +# This definition starts at one, prints it out and continues into a loop calling +# consider_prime on each iteration. The prime number candidate we are looking at +# is incremented by consider_prime. +# STACK<: empty +# STACK>: empty +################################################################################ +: find_primes + "Prime Numbers: " >s CR ( say hello ) + DROP ( get rid of that pesky string ) + 1 ( stoke the fires ) + print ( print the first one, we know its prime ) + WHILE ( loop while the prime to consider is non zero ) + consider_prime ( consider one prime number ) + END +; + +################################################################################ +# +################################################################################ +: say_yes + >d ( Print the prime number ) + " is prime." ( push string to output ) + >s ( output it ) + CR ( print carriage return ) + DROP ( pop string ) +; + +: say_no + >d ( Print the prime number ) + " is NOT prime." ( push string to put out ) + >s ( put out the string ) + CR ( print carriage return ) + DROP ( pop string ) +; + +################################################################################ +# This definition processes a single command line argument and determines if it +# is a prime number or not. +# STACK<: +# n - number of arguments +# arg1 - the prime numbers to examine +# STACK>: +# n-1 - one less than number of arguments +# arg2 - we processed one argument +################################################################################ +: do_one_argument + -- ( decrement loop counter ) + SWAP ( get the argument value ) + is_prime IF ( determine if its prime ) + say_yes ( uhuh ) + ELSE + say_no ( nope ) + ENDIF + DROP ( done with that argument ) +; + +################################################################################ +# The MAIN program just prints a banner and processes its arguments. +# STACK<: +# n - number of arguments +# ... - the arguments +################################################################################ +: process_arguments + WHILE ( while there are more arguments ) + do_one_argument ( process one argument ) + END +; + +################################################################################ +# The MAIN program just prints a banner and processes its arguments. +# STACK<: arguments +################################################################################ +: MAIN + NIP ( get rid of the program name ) + -- ( reduce number of arguments ) + DUP ( save the arg counter ) + 1 <= IF ( See if we got an argument ) + process_arguments ( tell user if they are prime ) + ELSE + find_primes ( see how many we can find ) + ENDIF + 0 ( push return code ) +; +</code> +</pre> +</div> +<!-- ======================================================================= --> +<div class="doc_section"> <a name="internal">Internals</a></div> +<div class="doc_text"> + <p><b>This section is under construction.</b> + <p>In the mean time, you can always read the code! It has comments!</p> +</div> +<!-- ======================================================================= --> +<div class="doc_subsection"> <a name="directory">Directory Structure</a></div> +<div class="doc_text"> +<p>The source code, test programs, and sample programs can all be found +in the LLVM repository named <tt>llvm-stacker</tt> This should be checked out to +the <tt>projects</tt> directory so that it will auto-configure. To do that, make +sure you have the llvm sources in <tt><i>llvm</i></tt> +(see <a href="GettingStarted.html">Getting Started</a>) and then use these +commands:<pre> + svn co http://llvm.org/svn/llvm-project/llvm-top/trunk llvm-top + cd llvm-top + make build MODULE=stacker +</p> +<p>Under the <tt>projects/llvm-stacker</tt> directory you will find the +implementation of the Stacker compiler, as follows:</p> +<ul> + <li><em>lib</em> - contains most of the source code + <ul> + <li><em>lib/compiler</em> - contains the compiler library + <li><em>lib/runtime</em> - contains the runtime library + </ul></li> + <li><em>test</em> - contains the test programs</li> + <li><em>tools</em> - contains the Stacker compiler main program, stkrc + <ul> + <li><em>lib/stkrc</em> - contains the Stacker compiler main program + </ul</li> + <li><em>sample</em> - contains the sample programs</li> +</ul> +</div> +<!-- ======================================================================= --> +<div class="doc_subsection"><a name="lexer"></a>The Lexer</div> +<div class="doc_text"> +<p>See projects/llvm-stacker/lib/compiler/Lexer.l</p> +</div> +<!-- ======================================================================= --> +<div class="doc_subsection"><a name="parser"></a>The Parser</div> +<div class="doc_text"> +<p>See projects/llvm-stacker/lib/compiler/StackerParser.y</p> +</div> +<!-- ======================================================================= --> +<div class="doc_subsection"><a name="compiler"></a>The Compiler</div> +<div class="doc_text"> +<p>See projects/llvm-stacker/lib/compiler/StackerCompiler.cpp</p> +</div> +<!-- ======================================================================= --> +<div class="doc_subsection"><a name="runtime"></a>The Runtime</div> +<div class="doc_text"> +<p>See projects/llvm-stacker/lib/runtime/stacker_rt.c</p> +</div> +<!-- ======================================================================= --> +<div class="doc_subsection"><a name="driver"></a>Compiler Driver</div> +<div class="doc_text"> +<p>See projects/llvm-stacker/tools/stkrc/stkrc.cpp</p> +</div> +<!-- ======================================================================= --> +<div class="doc_subsection"><a name="tests"></a>Test Programs</div> +<div class="doc_text"> +<p>See projects/llvm-stacker/test/*.st</p> +</div> +<!-- ======================================================================= --> +<div class="doc_subsection"> <a name="exercise">Exercise</a></div> +<div class="doc_text"> +<p>As you may have noted from a careful inspection of the Built-In word +definitions, the ROLL word is not implemented. This word was left out of +Stacker on purpose so that it can be an exercise for the student. The exercise +is to implement the ROLL functionality (in your own workspace) and build a test +program for it. If you can implement ROLL, you understand Stacker and probably +a fair amount about LLVM since this is one of the more complicated Stacker +operations. The work will almost be completely limited to the +<a href="#compiler">compiler</a>. +<p>The ROLL word is already recognized by both the lexer and parser but ignored +by the compiler. That means you don't have to futz around with figuring out how +to get the keyword recognized. It already is. The part of the compiler that +you need to implement is the <code>ROLL</code> case in the +<code>StackerCompiler::handle_word(int)</code> method.</p> See the +implementations of PICK and SELECT in the same method to get some hints about +how to complete this exercise.<p> +<p>Good luck!</p> +</div> +<!-- ======================================================================= --> +<div class="doc_subsection"><a name="todo">Things Remaining To Be Done</a></div> +<div class="doc_text"> +<p>The initial implementation of Stacker has several deficiencies. If you're +interested, here are some things that could be implemented better:</p> +<ol> + <li>Write an LLVM pass to compute the correct stack depth needed by the + program. Currently the stack is set to a fixed number which means programs + with large numbers of definitions might fail.</li> + <li>Write an LLVM pass to optimize the use of the global stack. The code + emitted currently is somewhat wasteful. It gets cleaned up a lot by existing + passes but more could be done.</li> + <li>Make the compiler driver use the LLVM linking facilities (with IPO) + before depending on GCC to do the final link.</li> + <li>Clean up parsing. It doesn't handle errors very well.</li> + <li>Rearrange the StackerCompiler.cpp code to make better use of inserting + instructions before a block's terminating instruction. I didn't figure this + technique out until I was nearly done with LLVM. As it is, its a bad example + of how to insert instructions!</li> + <li>Provide for I/O to arbitrary files instead of just stdin/stdout.</li> + <li>Write additional built-in words; with inspiration from FORTH</li> + <li>Write additional sample Stacker programs.</li> + <li>Add your own compiler writing experiences and tips in the + <a href="#lessons">Lessons I Learned About LLVM</a> section.</li> +</ol> +</div> + +<!-- *********************************************************************** --> + +<hr> +<address> + <a href="http://jigsaw.w3.org/css-validator/check/referer"><img + src="http://jigsaw.w3.org/css-validator/images/vcss" alt="Valid CSS!"></a> + <a href="http://validator.w3.org/check/referer"><img + src="http://www.w3.org/Icons/valid-html401" alt="Valid HTML 4.01!"></a> + + <a href="mailto:rspencer@x10sys.com">Reid Spencer</a><br> + <a href="http://llvm.org">LLVM Compiler Infrastructure</a><br> + Last modified: $Date$ +</address> + +</body> +</html> |