<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
<meta name="author" content="Chris Lattner">
<meta name="author" content="Erick Tryzelaar">
- <link rel="stylesheet" href="../llvm.css" type="text/css">
+ <link rel="stylesheet" href="../_static/llvm.css" type="text/css">
</head>
<body>
-<div class="doc_title">Kaleidoscope: Extending the Language: Control Flow</div>
+<h1>Kaleidoscope: Extending the Language: Control Flow</h1>
<ul>
<li><a href="index.html">Up to Tutorial Index</a></li>
</div>
<!-- *********************************************************************** -->
-<div class="doc_section"><a name="intro">Chapter 5 Introduction</a></div>
+<h2><a name="intro">Chapter 5 Introduction</a></h2>
<!-- *********************************************************************** -->
-<div class="doc_text">
+<div>
<p>Welcome to Chapter 5 of the "<a href="index.html">Implementing a language
with LLVM</a>" tutorial. Parts 1-4 described the implementation of the simple
</div>
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-<div class="doc_section"><a name="ifthen">If/Then/Else</a></div>
+<h2><a name="ifthen">If/Then/Else</a></h2>
<!-- *********************************************************************** -->
-<div class="doc_text">
+<div>
<p>
Extending Kaleidoscope to support if/then/else is quite straightforward. It
<p>Now that we know what we "want", lets break this down into its constituent
pieces.</p>
-</div>
-
<!-- ======================================================================= -->
-<div class="doc_subsubsection"><a name="iflexer">Lexer Extensions for
-If/Then/Else</a></div>
+<h4><a name="iflexer">Lexer Extensions for If/Then/Else</a></h4>
<!-- ======================================================================= -->
-<div class="doc_text">
+<div>
<p>The lexer extensions are straightforward. First we add new variants
for the relevant tokens:</p>
</div>
<!-- ======================================================================= -->
-<div class="doc_subsubsection"><a name="ifast">AST Extensions for
- If/Then/Else</a></div>
+<h4><a name="ifast">AST Extensions for If/Then/Else</a></h4>
<!-- ======================================================================= -->
-<div class="doc_text">
+<div>
<p>To represent the new expression we add a new AST variant for it:</p>
</div>
<!-- ======================================================================= -->
-<div class="doc_subsubsection"><a name="ifparser">Parser Extensions for
-If/Then/Else</a></div>
+<h4><a name="ifparser">Parser Extensions for If/Then/Else</a></h4>
<!-- ======================================================================= -->
-<div class="doc_text">
+<div>
<p>Now that we have the relevant tokens coming from the lexer and we have the
AST node to build, our parsing logic is relatively straightforward. First we
</div>
<!-- ======================================================================= -->
-<div class="doc_subsubsection"><a name="ifir">LLVM IR for If/Then/Else</a></div>
+<h4><a name="ifir">LLVM IR for If/Then/Else</a></h4>
<!-- ======================================================================= -->
-<div class="doc_text">
+<div>
<p>Now that we have it parsing and building the AST, the final piece is adding
LLVM code generation support. This is the most interesting part of the
</div>
<!-- ======================================================================= -->
-<div class="doc_subsubsection"><a name="ifcodegen">Code Generation for
-If/Then/Else</a></div>
+<h4><a name="ifcodegen">Code Generation for If/Then/Else</a></h4>
<!-- ======================================================================= -->
-<div class="doc_text">
+<div>
<p>In order to generate code for this, we implement the <tt>Codegen</tt> method
for <tt>IfExprAST</tt>:</p>
</div>
+</div>
+
<!-- *********************************************************************** -->
-<div class="doc_section"><a name="for">'for' Loop Expression</a></div>
+<h2><a name="for">'for' Loop Expression</a></h2>
<!-- *********************************************************************** -->
-<div class="doc_text">
+<div>
<p>Now that we know how to add basic control flow constructs to the language,
we have the tools to add more powerful things. Lets add something more
<p>As before, lets talk about the changes that we need to Kaleidoscope to
support this.</p>
-</div>
-
<!-- ======================================================================= -->
-<div class="doc_subsubsection"><a name="forlexer">Lexer Extensions for
-the 'for' Loop</a></div>
+<h4><a name="forlexer">Lexer Extensions for the 'for' Loop</a></h4>
<!-- ======================================================================= -->
-<div class="doc_text">
+<div>
<p>The lexer extensions are the same sort of thing as for if/then/else:</p>
</div>
<!-- ======================================================================= -->
-<div class="doc_subsubsection"><a name="forast">AST Extensions for
-the 'for' Loop</a></div>
+<h4><a name="forast">AST Extensions for the 'for' Loop</a></h4>
<!-- ======================================================================= -->
-<div class="doc_text">
+<div>
<p>The AST variant is just as simple. It basically boils down to capturing
the variable name and the constituent expressions in the node.</p>
</div>
<!-- ======================================================================= -->
-<div class="doc_subsubsection"><a name="forparser">Parser Extensions for
-the 'for' Loop</a></div>
+<h4><a name="forparser">Parser Extensions for the 'for' Loop</a></h4>
<!-- ======================================================================= -->
-<div class="doc_text">
+<div>
<p>The parser code is also fairly standard. The only interesting thing here is
handling of the optional step value. The parser code handles it by checking to
</div>
<!-- ======================================================================= -->
-<div class="doc_subsubsection"><a name="forir">LLVM IR for
-the 'for' Loop</a></div>
+<h4><a name="forir">LLVM IR for the 'for' Loop</a></h4>
<!-- ======================================================================= -->
-<div class="doc_text">
+<div>
<p>Now we get to the good part: the LLVM IR we want to generate for this thing.
With the simple example above, we get this LLVM IR (note that this dump is
</div>
<!-- ======================================================================= -->
-<div class="doc_subsubsection"><a name="forcodegen">Code Generation for
-the 'for' Loop</a></div>
+<h4><a name="forcodegen">Code Generation for the 'for' Loop</a></h4>
<!-- ======================================================================= -->
-<div class="doc_text">
+<div>
<p>The first part of Codegen is very simple: we just output the start expression
for the loop value:</p>
</div>
+</div>
+
<!-- *********************************************************************** -->
-<div class="doc_section"><a name="code">Full Code Listing</a></div>
+<h2><a name="code">Full Code Listing</a></h2>
<!-- *********************************************************************** -->
-<div class="doc_text">
+<div>
<p>
Here is the complete code listing for our running example, enhanced with the
(* Set up the optimizer pipeline. Start with registering info about how the
* target lays out data structures. *)
- TargetData.add (ExecutionEngine.target_data the_execution_engine) the_fpm;
+ DataLayout.add (ExecutionEngine.target_data the_execution_engine) the_fpm;
(* Do simple "peephole" optimizations and bit-twiddling optzn. *)
add_instruction_combination the_fpm;
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