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- <title>Stacker: An Example Of Using LLVM</title>
+ <title>Stacker: An Example Of Using LLVM</title>
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<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><a href="#punctuation">Punctuation</a>
- <li><a href="#literals">Literals</a>
- <li><a href="#words">Words</a>
- <li><a href="#builtins">Built-Ins</a>
- </ol>
- </li>
- <li><a href="#directory">The Directory Structure </a>
+ <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_text">
-<p><b>Written by <a href="mailto:rspencer@x10sys.com">Reid Spencer</a> </b></p>
-<p> </p>
+
+<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_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>, this
-document walks you through the implementation of a programming language
-named Stacker. Stacker was invented specifically as a demonstration of
+<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
+intricacies of LLVM itself but on how to use it to build your own
compiler system.</p>
</div>
<!-- ======================================================================= -->
<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, the author of Stacker 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 up when using LLVM. Furthermore, this was the <em >first</em>
+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
+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; its very simple. Although it is computationally
+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, its simple, and it <em>doesn't</em> have
+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 language syntaxes.</p>
+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
: 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
+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 onto the stack, print it out
+<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
<p>Exercise for the reader: how could you make this a one line program?</p>
</div>
<!-- ======================================================================= -->
-<div class="doc_section"><a name="stack"></a>Lessons Learned About LLVM</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: (a) to get the author over the
-learning curve and (b) to provide a simple example of how to write a compiler
-using LLVM. During the development of Stacker, many lessons about LLVM were
+<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 = BasicBlock::Create();
+bb->getInstList().push_back( BranchInst::Create( ... ) );
+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 = BasicBlock::Create();
+ BasicBlock* else_bb = BasicBlock::Create();
+ BasicBlock* exit_bb = BasicBlock::Create();
+
+ // Insert the branch instruction for the "if"
+ bb->getInstList().push_back( BranchInst::Create( then_bb, else_bb, condition ) );
+
+ // Set up the terminating instructions
+ then->getInstList().push_back( BranchInst::Create( exit_bb ) );
+ else->getInstList().push_back( BranchInst::Create( 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 = GetElementPtrInst::Create( 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>To be completed.</p></div>
-<div class="doc_subsection"><a name="linkage"></a>Everything's a Value!</div>
-<div class="doc_text"><p>To be completed.</p></div>
-<div class="doc_subsection"><a name="linkage"></a>The Wily GetElementPtrInst</div>
-<div class="doc_text"><p>To be completed.</p></div>
-<div class="doc_subsection"><a name="linkage"></a>Constants Are Easier Than That!</div>
-<div class="doc_text"><p>To be completed.</p></div>
-<div class="doc_subsection"><a name="linkage"></a>Terminate Those Blocks!</div>
-<div class="doc_text"><p>To be completed.</p></div>
-<div class="doc_subsection"><a name="linkage"></a>new,get,create .. Its All The Same</div>
-<div class="doc_text"><p>To be completed.</p></div>
-<div class="doc_subsection"><a name="linkage"></a>Utility Functions To The Rescue</div>
-<div class="doc_text"><p>To be completed.</p></div>
-<div class="doc_subsection"><a name="linkage"></a>push_back Is Your Friend</div>
-<div class="doc_text"><p>To be completed.</p></div>
-<div class="doc_subsection"><a name="linkage"></a>Block Heads Come First</div>
-<div class="doc_text"><p>To be completed.</p></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 to of the stack. All of this is hidden from the
-programmer but it needs to be noted because it is the foundation of the
+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
+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>
+on interpretation of the stack values. You've been warned. :) </p>
</div>
<!-- ======================================================================= -->
<div class="doc_subsection"> <a name="punctuation"></a>Punctuation</div>
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 semi-colon comes the name of the word being defined.
-The remaining words in the definition specify what the word does.</p>
+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. Integer, Strings,
+ <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 onto the stack. So, for example:<br/>
+ value on to the stack. So, for example:<br/>
<code> 42 " is the answer." TRUE </code><br/>
- will push three values onto the stack: the integer 42, the
- string " is the answer." and the boolean TRUE.</p>
+ 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>
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 words definition to be invoked. It
+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 below.</p>
+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>
+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
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
+ <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
+ <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
+ <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 DUP SWAP OVER ROT DUP2 DROP2 PICK TUCK</li>
- <li><em>Memory></em>These words allocate, free and manipulate memory
+ 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
+ <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
+ <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>
<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's memory block</li>
+ <li><em>p</em> - a pointer to a malloc'd memory block</li>
</ol>
</div>
-<div class="doc_text">
-<table class="doc_table" >
-<tr class="doc_table"><td colspan="4">Definition Of Operation Of Built In Words</td></tr>
-<tr class="doc_table"><td colspan="4">LOGICAL OPERATIONS</td></tr>
-<tr class="doc_table"><td>Word</td><td>Name</td><td>Operation</td><td>Description</td></tr>
-<tr class="doc_table"><td><</td>
+<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
<tr><td>FALSE</td>
<td>FALSE</td>
<td> -- b</td>
- <td>The boolean value FALSE (0) is pushed onto the stack.</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 onto the stack.</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 colspan="4">BITWISE OPERATIONS</td></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>
are bitwise exclusive OR'd together and pushed back on the stack.
For example, The sequence 1 3 XOR yields 2.</td>
</tr>
-<tr><td colspan="4">ARITHMETIC OPERATIONS</td></tr>
-<tr><td>Word</td><td>Name</td><td>Operation</td><td>Description</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 onto the stack. If w1 is -1 then w2 is 1. If w1 is
+ 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 onto the stack. If w1 is -1 then w2 is 1. If w1 is
+ 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
- onto the stack</td>
+ 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
- onto the stack</td>
+ 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
- onto the stack</td>
+ 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
- onto the stack</td>
+ 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 onto the stack</td>
+ 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 onto the stack.</td>
+ 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 onto the stack.</td>
+ 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 onto the stack.</td>
+ 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
- onto the stack.</td>
+ 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
- onto the stack.</td>
+ 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 colspan="4">STACK MANIPULATION OPERATIONS</td></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>
<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 onto
+ <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>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 onto the stack in
+ 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>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 onto the stack in the reverse order but
- in pairs.</p>
+ 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
- onto the stack in the order w1 w2 w1. This seems to cause the
+ 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 onto the
+ <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 onto the stack in the order
+ off the stack. They are pushed back on to the stack in the order
w1 w3 w2.</td>
</tr>
<tr><td>ROT2</td>
</tr>
<tr><td>RROT</td>
<td>RROT</td>
- <td>w1 w2 w3 -- w2 w3 w1</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>
<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. If you can implement this one you understand Stacker
- and probably a fair amount about LLVM since this is one of the
- more complicated Stacker operations. See the StackerCompiler.cpp
- file in the projects/Stacker/lib/compiler directory. The operation
- of ROLL is like a generalized ROT. That is ROLL with n=1 is the
- same as ROT. The n value (top of stack) is used as an index to
- select a value up the stack that is <em>moved</em> to the top of
- the stack. See the implementations of PICk and SELECT to get
- some hints.<p>
-</tr>
-<tr><td colspan="4">MEMORY OPERATIONS</td></tr>
-<tr><td>Word</td><td>Name</td><td>Operation</td><td>Description</td></tr>
+ 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 onto the stack.</td>
+ block is pushed on to the stack.</td>
</tr>
<tr><td>FREE</td>
<td>FREE</td>
pushed back on the stack so this doesn't count as a "use ptr"
in the FREE idiom.</td>
</tr>
-<tr><td colspan="4">CONTROL FLOW OPERATIONS</td></tr>
-<tr><td>Word</td><td>Name</td><td>Operation</td><td>Description</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>
executed. In either case, after the (words....) have executed, execution continues
immediately following the ENDIF. </td>
</tr>
-<tr><td>WHILE (words...) END</td>
- <td>WHILE (words...) END</td>
+<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. If it is non-zero then the
- "words..." between WHILE and END are executed. Execution then begins again at the WHILE where another
- boolean is popped off the stack. To prevent this operation from eating up the entire
- stack, you should push onto the stack (just before the END) a boolean value that indicates
- whether to terminate. Note that since booleans and integers can be coerced you can
- use the following "for loop" idiom:<br/>
- <code>(push count) WHILE (words...) -- END</code><br/>
+ <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 DUP >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 duplicated and then
- 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 the WHILE test fails and control is
- transfered to the word after the END.</td>
-</tr>
-<tr><td colspan="4">INPUT & OUTPUT OPERATIONS</td></tr>
-<tr><td>Word</td><td>Name</td><td>Operation</td><td>Description</td></tr>
+ <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>
<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>
+ <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>
+ <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 onto the stack.</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 onto the stack</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 onto the stack.</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>
to see instantly the net effect of the definition.</td>
</tr>
</table>
+
</div>
<!-- ======================================================================= -->
-<div class="doc_section"> <a name="directory">Directory Structure</a></div>
-<div class="doc_text">
-<p>The source code, test programs, and sample programs can all be found
-under the LLVM "projects" directory. You will need to obtain the LLVM sources
-to find it (either via anonymous CVS or a tarball. See the
-<a href="GettingStarted.html">Getting Started</a> document).</p>
-<p>Under the "projects" directory there is a directory named "stacker". That
-directory contains everything, 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_section"> <a name="directory">Prime: A Complete Example</a></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 of features of both
-the Stacker language and what is possible with LLVM. The program simply
-prints out the prime numbers until it reaches
+<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">
-<p><code>
-<![CDATA[
+<pre><code>
################################################################################
#
# Brute force prime number generator
################################################################################
# Utility definitions
################################################################################
-: print >d CR ;
+: print >d CR ;
: it_is_a_prime TRUE ;
: it_is_not_a_prime FALSE ;
: continue_loop TRUE ;
: exit_loop FALSE;
################################################################################
-# This definition tryies an actual division of a candidate prime number. It
+# 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<:
+# STACK<:
# div - the divisor to try
# p - the prime number we are working on
-# STACK>:
+# STACK>:
# cont - should we continue the loop ?
# div - the next divisor to try
# p - the prime number we are working on
# cont - should we continue the loop (ignored)?
# div - the divisor to try
# p - the prime number we are working on
-# STACK>:
+# STACK>:
# cont - should we continue the loop ?
# div - the next divisor to try
# p - the prime number we are working on
# 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<:
+# STACK<:
# p - the prime number to check
-# STACK>:
-# yn - boolean indiating if its a prime or not
+# STACK>:
+# yn - boolean indicating if its a prime or not
# p - the prime number checked
################################################################################
: try_harder
################################################################################
# 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
+# 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<:
+# STACK<:
# p - the prime number to check
-# STACK>:
+# 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 )
+ 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 )
################################################################################
# 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
+# STACK<: ignored
+# STACK>: exits
################################################################################
: done
- "Finished" >s CR ( say we are finished )
+ "Finished" >s CR ( say we are finished )
0 EXIT ( exit nicely )
;
# 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<:
+# STACK<:
# p - one less than the prime number to consider
-# STACK>
+# 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 )
+ 1000000 < IF ( check to see if we are done yet )
done ( we are done, call "done" )
ENDIF
++ ( increment to next prime number )
# 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
+# STACK<: empty
+# STACK>: empty
################################################################################
: find_primes
- "Prime Numbers: " >s CR ( say hello )
+ "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 )
#
################################################################################
: say_yes
- >d ( Print the prime number )
+ >d ( Print the prime number )
" is prime." ( push string to output )
- >s ( output it )
+ >s ( output it )
CR ( print carriage return )
DROP ( pop string )
;
: say_no
- >d ( Print the prime number )
+ >d ( Print the prime number )
" is NOT prime." ( push string to put out )
- >s ( put out the string )
+ >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<:
+# STACK<:
# n - number of arguments
# arg1 - the prime numbers to examine
-# STACK>:
+# STACK>:
# n-1 - one less than number of arguments
# arg2 - we processed one argument
################################################################################
################################################################################
# The MAIN program just prints a banner and processes its arguments.
-# STACK<:
+# STACK<:
# n - number of arguments
# ... - the arguments
################################################################################
################################################################################
# The MAIN program just prints a banner and processes its arguments.
-# STACK<: 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 )
+ 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>
-</p>
+</pre>
</div>
<!-- ======================================================================= -->
-<div class="doc_section"> <a name="lexicon">Internals</a></div>
-<div class="doc_text"><p>To be completed.</p></div>
-<div class="doc_subsection"><a name="stack"></a>The Lexer</div>
-<div class="doc_subsection"><a name="stack"></a>The Parser</div>
-<div class="doc_subsection"><a name="stack"></a>The Compiler</div>
-<div class="doc_subsection"><a name="stack"></a>The Stack</div>
-<div class="doc_subsection"><a name="stack"></a>Definitions Are Functions</div>
-<div class="doc_subsection"><a name="stack"></a>Words Are BasicBlocks</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:</p>
+
+<div class="doc_code">
+<pre>
+% svn co http://llvm.org/svn/llvm-project/llvm-top/trunk llvm-top
+% cd llvm-top
+% make build MODULE=stacker
+</pre>
+</div>
+
+<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>
-<div class="doc_footer">
-<address><a href="mailto:rspencer@x10sys.com">Reid Spencer</a></address>
-<a href="http://llvm.cs.uiuc.edu">The LLVM Compiler Infrastructure</a>
-<br>Last modified: $Date$ </div>
+<address>
+ <a href="http://jigsaw.w3.org/css-validator/check/referer"><img
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+
+ <a href="mailto:rspencer@x10sys.com">Reid Spencer</a><br>
+ <a href="http://llvm.org">LLVM Compiler Infrastructure</a><br>
+ Last modified: $Date$
+</address>
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