mirror of
https://github.com/ganelson/inform.git
synced 2024-07-16 22:14:23 +03:00
181 lines
21 KiB
HTML
181 lines
21 KiB
HTML
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
|
|
<html>
|
|
<head>
|
|
<title>Eliminate Redundant Labels Stage</title>
|
|
<link href="../docs-assets/Breadcrumbs.css" rel="stylesheet" rev="stylesheet" type="text/css">
|
|
<meta name="viewport" content="width=device-width initial-scale=1">
|
|
<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
|
|
<meta http-equiv="Content-Language" content="en-gb">
|
|
|
|
<link href="../docs-assets/Contents.css" rel="stylesheet" rev="stylesheet" type="text/css">
|
|
<link href="../docs-assets/Progress.css" rel="stylesheet" rev="stylesheet" type="text/css">
|
|
<link href="../docs-assets/Navigation.css" rel="stylesheet" rev="stylesheet" type="text/css">
|
|
<link href="../docs-assets/Fonts.css" rel="stylesheet" rev="stylesheet" type="text/css">
|
|
<link href="../docs-assets/Base.css" rel="stylesheet" rev="stylesheet" type="text/css">
|
|
<script>
|
|
function togglePopup(material_id) {
|
|
var popup = document.getElementById(material_id);
|
|
popup.classList.toggle("show");
|
|
}
|
|
</script>
|
|
|
|
<link href="../docs-assets/Popups.css" rel="stylesheet" rev="stylesheet" type="text/css">
|
|
<link href="../docs-assets/Colours.css" rel="stylesheet" rev="stylesheet" type="text/css">
|
|
|
|
</head>
|
|
<body class="commentary-font">
|
|
<nav role="navigation">
|
|
<h1><a href="../index.html">
|
|
<img src="../docs-assets/Inform.png" height=72">
|
|
</a></h1>
|
|
<ul><li><a href="../index.html">home</a></li>
|
|
</ul><h2>Compiler</h2><ul>
|
|
<li><a href="../structure.html">structure</a></li>
|
|
<li><a href="../inbuildn.html">inbuild</a></li>
|
|
<li><a href="../inform7n.html">inform7</a></li>
|
|
<li><a href="../intern.html">inter</a></li>
|
|
<li><a href="../services.html">services</a></li>
|
|
<li><a href="../secrets.html">secrets</a></li>
|
|
</ul><h2>Other Tools</h2><ul>
|
|
<li><a href="../inblorbn.html">inblorb</a></li>
|
|
<li><a href="../indocn.html">indoc</a></li>
|
|
<li><a href="../inform6.html">inform6</a></li>
|
|
<li><a href="../inpolicyn.html">inpolicy</a></li>
|
|
<li><a href="../inrtpsn.html">inrtps</a></li>
|
|
</ul><h2>Resources</h2><ul>
|
|
<li><a href="../extensions.html">extensions</a></li>
|
|
<li><a href="../kits.html">kits</a></li>
|
|
</ul><h2>Repository</h2><ul>
|
|
<li><a href="https://github.com/ganelson/inform"><img src="../docs-assets/github.png" height=18> github</a></li>
|
|
</ul><h2>Related Projects</h2><ul>
|
|
<li><a href="../../../inweb/index.html">inweb</a></li>
|
|
<li><a href="../../../intest/index.html">intest</a></li>
|
|
|
|
</ul>
|
|
</nav>
|
|
<main role="main">
|
|
<!--Weave of 'Eliminate Redundant Labels Stage' generated by Inweb-->
|
|
<div class="breadcrumbs">
|
|
<ul class="crumbs"><li><a href="../index.html">Home</a></li><li><a href="../intern.html">Inter Modules</a></li><li><a href="index.html">pipeline</a></li><li><a href="index.html#6">Chapter 6: Optimisation</a></li><li><b>Eliminate Redundant Labels Stage</b></li></ul></div>
|
|
<p class="purpose">To remove labels which are defined but never jumped to.</p>
|
|
|
|
<p class="commentary firstcommentary"><a id="SP1" class="paragraph-anchor"></a><b>§1. </b><a href="../inform7/index.html" class="internal">inform7</a> tends to produce a lot of labels when compiling complicated text
|
|
substitutions, but many — around 2000 in a typical run — are never branched to,
|
|
either by a jump invocation or by assembly language.
|
|
</p>
|
|
|
|
<p class="commentary">These spurious labels cause no real problem except untidiness, but removing
|
|
them provides a simple example of how peephole optimisation can be performed
|
|
on an Inter tree.
|
|
</p>
|
|
|
|
<pre class="displayed-code all-displayed-code code-font">
|
|
<span class="reserved-syntax">void</span><span class="plain-syntax"> </span><span class="function-syntax">EliminateRedundantLabelsStage::create_pipeline_stage</span><button class="popup" onclick="togglePopup('usagePopup1')"><span class="comment-syntax">?</span><span class="popuptext" id="usagePopup1">Usage of <span class="code-font"><span class="function-syntax">EliminateRedundantLabelsStage::create_pipeline_stage</span></span>:<br/>Parsing Pipelines - <a href="2-pp.html#SP10">§10</a></span></button><span class="plain-syntax">(</span><span class="reserved-syntax">void</span><span class="plain-syntax">) {</span>
|
|
<span class="plain-syntax"> </span><a href="2-pp.html#SP3" class="function-link"><span class="function-syntax">ParsingPipelines::new_stage</span></a><span class="plain-syntax">(</span><span class="identifier-syntax">I</span><span class="string-syntax">"eliminate-redundant-labels"</span><span class="plain-syntax">,</span>
|
|
<span class="plain-syntax"> </span><a href="6-erls.html#SP1" class="function-link"><span class="function-syntax">EliminateRedundantLabelsStage::run</span></a><span class="plain-syntax">, </span><span class="constant-syntax">NO_STAGE_ARG</span><span class="plain-syntax">, </span><span class="identifier-syntax">FALSE</span><span class="plain-syntax">);</span>
|
|
<span class="plain-syntax">}</span>
|
|
|
|
<span class="reserved-syntax">int</span><span class="plain-syntax"> </span><span class="identifier-syntax">redundant_labels_removed</span><span class="plain-syntax"> = </span><span class="constant-syntax">0</span><span class="plain-syntax">;</span>
|
|
<span class="reserved-syntax">int</span><span class="plain-syntax"> </span><span class="function-syntax">EliminateRedundantLabelsStage::run</span><span class="plain-syntax">(</span><span class="reserved-syntax">pipeline_step</span><span class="plain-syntax"> *</span><span class="identifier-syntax">step</span><span class="plain-syntax">) {</span>
|
|
<span class="plain-syntax"> </span><span class="identifier-syntax">redundant_labels_removed</span><span class="plain-syntax"> = </span><span class="constant-syntax">0</span><span class="plain-syntax">;</span>
|
|
<span class="plain-syntax"> </span><span class="identifier-syntax">InterTree::traverse</span><span class="plain-syntax">(</span><span class="identifier-syntax">step</span><span class="plain-syntax">-></span><span class="element-syntax">ephemera</span><span class="plain-syntax">.</span><span class="element-syntax">tree</span><span class="plain-syntax">,</span>
|
|
<span class="plain-syntax"> </span><a href="6-erls.html#SP1" class="function-link"><span class="function-syntax">EliminateRedundantLabelsStage::visitor</span></a><span class="plain-syntax">, </span><span class="identifier-syntax">NULL</span><span class="plain-syntax">, </span><span class="identifier-syntax">NULL</span><span class="plain-syntax">, </span><span class="identifier-syntax">PACKAGE_IST</span><span class="plain-syntax">);</span>
|
|
<span class="plain-syntax"> </span><span class="reserved-syntax">if</span><span class="plain-syntax"> (</span><span class="identifier-syntax">redundant_labels_removed</span><span class="plain-syntax"> > </span><span class="constant-syntax">0</span><span class="plain-syntax">)</span>
|
|
<span class="plain-syntax"> </span><span class="identifier-syntax">LOG</span><span class="plain-syntax">(</span><span class="string-syntax">"%d redundant label(s) removed\n"</span><span class="plain-syntax">, </span><span class="identifier-syntax">redundant_labels_removed</span><span class="plain-syntax">);</span>
|
|
<span class="plain-syntax"> </span><span class="reserved-syntax">return</span><span class="plain-syntax"> </span><span class="identifier-syntax">TRUE</span><span class="plain-syntax">;</span>
|
|
<span class="plain-syntax">}</span>
|
|
|
|
<span class="reserved-syntax">void</span><span class="plain-syntax"> </span><span class="function-syntax">EliminateRedundantLabelsStage::visitor</span><span class="plain-syntax">(</span><span class="identifier-syntax">inter_tree</span><span class="plain-syntax"> *</span><span class="identifier-syntax">I</span><span class="plain-syntax">, </span><span class="identifier-syntax">inter_tree_node</span><span class="plain-syntax"> *</span><span class="identifier-syntax">P</span><span class="plain-syntax">, </span><span class="reserved-syntax">void</span><span class="plain-syntax"> *</span><span class="identifier-syntax">state</span><span class="plain-syntax">) {</span>
|
|
<span class="plain-syntax"> </span><span class="identifier-syntax">inter_package</span><span class="plain-syntax"> *</span><span class="identifier-syntax">pack</span><span class="plain-syntax"> = </span><span class="identifier-syntax">PackageInstruction::at_this_head</span><span class="plain-syntax">(</span><span class="identifier-syntax">P</span><span class="plain-syntax">);</span>
|
|
<span class="plain-syntax"> </span><span class="reserved-syntax">if</span><span class="plain-syntax"> (</span><span class="identifier-syntax">InterPackage::is_a_function_body</span><span class="plain-syntax">(</span><span class="identifier-syntax">pack</span><span class="plain-syntax">))</span>
|
|
<span class="plain-syntax"> </span><span class="named-paragraph-container code-font"><a href="6-erls.html#SP1_1" class="named-paragraph-link"><span class="named-paragraph">Perform peephole optimisation on this function body</span><span class="named-paragraph-number">1.1</span></a></span><span class="plain-syntax">;</span>
|
|
<span class="plain-syntax">}</span>
|
|
</pre>
|
|
<p class="commentary firstcommentary"><a id="SP1_1" class="paragraph-anchor"></a><b>§1.1. </b><span class="named-paragraph-container code-font"><span class="named-paragraph-defn">Perform peephole optimisation on this function body</span><span class="named-paragraph-number">1.1</span></span><span class="comment-syntax"> =</span>
|
|
</p>
|
|
|
|
<pre class="displayed-code all-displayed-code code-font">
|
|
<span class="plain-syntax"> </span><span class="identifier-syntax">inter_symbols_table</span><span class="plain-syntax"> *</span><span class="identifier-syntax">local_symbols</span><span class="plain-syntax"> = </span><span class="identifier-syntax">InterPackage::scope</span><span class="plain-syntax">(</span><span class="identifier-syntax">pack</span><span class="plain-syntax">);</span>
|
|
<span class="plain-syntax"> </span><span class="named-paragraph-container code-font"><a href="6-erls.html#SP1_1_1" class="named-paragraph-link"><span class="named-paragraph">Mark all the labels for this function as being unused</span><span class="named-paragraph-number">1.1.1</span></a></span><span class="plain-syntax">;</span>
|
|
<span class="plain-syntax"> </span><span class="named-paragraph-container code-font"><a href="6-erls.html#SP1_1_2" class="named-paragraph-link"><span class="named-paragraph">Look through the function for mentions of labels, marking those as used</span><span class="named-paragraph-number">1.1.2</span></a></span><span class="plain-syntax">;</span>
|
|
<span class="plain-syntax"> </span><span class="named-paragraph-container code-font"><a href="6-erls.html#SP1_1_3" class="named-paragraph-link"><span class="named-paragraph">Remove the label declarations for any that are still marked unused</span><span class="named-paragraph-number">1.1.3</span></a></span><span class="plain-syntax">;</span>
|
|
</pre>
|
|
<ul class="endnotetexts"><li>This code is used in <a href="6-erls.html#SP1">§1</a>.</li></ul>
|
|
<p class="commentary firstcommentary"><a id="SP1_1_1" class="paragraph-anchor"></a><b>§1.1.1. </b>The symbol flag <span class="extract"><span class="extract-syntax">USED_MARK_ISYMF</span></span> is free for us to use, but its value for
|
|
any given symbol is undefined when we begin. We'll clear it for all labels.
|
|
</p>
|
|
|
|
<p class="commentary"><span class="named-paragraph-container code-font"><span class="named-paragraph-defn">Mark all the labels for this function as being unused</span><span class="named-paragraph-number">1.1.1</span></span><span class="comment-syntax"> =</span>
|
|
</p>
|
|
|
|
<pre class="displayed-code all-displayed-code code-font">
|
|
<span class="plain-syntax"> </span><span class="identifier-syntax">LOOP_OVER_SYMBOLS_TABLE</span><span class="plain-syntax">(</span><span class="identifier-syntax">S</span><span class="plain-syntax">, </span><span class="identifier-syntax">local_symbols</span><span class="plain-syntax">)</span>
|
|
<span class="plain-syntax"> </span><span class="reserved-syntax">if</span><span class="plain-syntax"> (</span><span class="identifier-syntax">InterSymbol::is_label</span><span class="plain-syntax">(</span><span class="identifier-syntax">S</span><span class="plain-syntax">))</span>
|
|
<span class="plain-syntax"> </span><span class="identifier-syntax">InterSymbol::clear_flag</span><span class="plain-syntax">(</span><span class="identifier-syntax">S</span><span class="plain-syntax">, </span><span class="identifier-syntax">USED_MARK_ISYMF</span><span class="plain-syntax">);</span>
|
|
</pre>
|
|
<ul class="endnotetexts"><li>This code is used in <a href="6-erls.html#SP1_1">§1.1</a>.</li></ul>
|
|
<p class="commentary firstcommentary"><a id="SP1_1_2" class="paragraph-anchor"></a><b>§1.1.2. </b><span class="named-paragraph-container code-font"><span class="named-paragraph-defn">Look through the function for mentions of labels, marking those as used</span><span class="named-paragraph-number">1.1.2</span></span><span class="comment-syntax"> =</span>
|
|
</p>
|
|
|
|
<pre class="displayed-code all-displayed-code code-font">
|
|
<span class="plain-syntax"> </span><span class="identifier-syntax">inter_tree_node</span><span class="plain-syntax"> *</span><span class="identifier-syntax">D</span><span class="plain-syntax"> = </span><span class="identifier-syntax">InterPackage::head</span><span class="plain-syntax">(</span><span class="identifier-syntax">pack</span><span class="plain-syntax">);</span>
|
|
<span class="plain-syntax"> </span><a href="6-erls.html#SP2" class="function-link"><span class="function-syntax">EliminateRedundantLabelsStage::traverse_code_tree</span></a><span class="plain-syntax">(</span><span class="identifier-syntax">D</span><span class="plain-syntax">);</span>
|
|
</pre>
|
|
<ul class="endnotetexts"><li>This code is used in <a href="6-erls.html#SP1_1">§1.1</a>.</li></ul>
|
|
<p class="commentary firstcommentary"><a id="SP1_1_3" class="paragraph-anchor"></a><b>§1.1.3. </b>Anything not marked used must be unused, so we can get rid of it. We do this
|
|
by striking its definition; the definition of a label symbol is the line
|
|
which shows where it belongs in the function (written <span class="extract"><span class="extract-syntax">.Example</span></span> in Inter
|
|
syntax). Striking this does two things: it removes the definition line; and
|
|
it renders the symbol undefined. It still lives on in the function's symbols
|
|
table, though, and (since we have made sure there are no references to it from
|
|
anywhere) we may as well remove it.
|
|
</p>
|
|
|
|
<p class="commentary"><span class="named-paragraph-container code-font"><span class="named-paragraph-defn">Remove the label declarations for any that are still marked unused</span><span class="named-paragraph-number">1.1.3</span></span><span class="comment-syntax"> =</span>
|
|
</p>
|
|
|
|
<pre class="displayed-code all-displayed-code code-font">
|
|
<span class="plain-syntax"> </span><span class="identifier-syntax">LOOP_OVER_SYMBOLS_TABLE</span><span class="plain-syntax">(</span><span class="identifier-syntax">S</span><span class="plain-syntax">, </span><span class="identifier-syntax">local_symbols</span><span class="plain-syntax">)</span>
|
|
<span class="plain-syntax"> </span><span class="reserved-syntax">if</span><span class="plain-syntax"> (</span><span class="identifier-syntax">InterSymbol::is_label</span><span class="plain-syntax">(</span><span class="identifier-syntax">S</span><span class="plain-syntax">))</span>
|
|
<span class="plain-syntax"> </span><span class="reserved-syntax">if</span><span class="plain-syntax"> (</span><span class="identifier-syntax">InterSymbol::get_flag</span><span class="plain-syntax">(</span><span class="identifier-syntax">S</span><span class="plain-syntax">, </span><span class="identifier-syntax">USED_MARK_ISYMF</span><span class="plain-syntax">) == </span><span class="identifier-syntax">FALSE</span><span class="plain-syntax">) {</span>
|
|
<span class="plain-syntax"> </span><span class="identifier-syntax">InterSymbol::strike_definition</span><span class="plain-syntax">(</span><span class="identifier-syntax">S</span><span class="plain-syntax">);</span>
|
|
<span class="plain-syntax"> </span><span class="identifier-syntax">InterSymbolsTable::remove_symbol</span><span class="plain-syntax">(</span><span class="identifier-syntax">S</span><span class="plain-syntax">);</span>
|
|
<span class="plain-syntax"> </span><span class="identifier-syntax">redundant_labels_removed</span><span class="plain-syntax">++;</span>
|
|
<span class="plain-syntax"> }</span>
|
|
</pre>
|
|
<ul class="endnotetexts"><li>This code is used in <a href="6-erls.html#SP1_1">§1.1</a>.</li></ul>
|
|
<p class="commentary firstcommentary"><a id="SP2" class="paragraph-anchor"></a><b>§2. </b>The following visits every line of code in the function, in the same order
|
|
it would be written out in a listing.
|
|
</p>
|
|
|
|
<pre class="displayed-code all-displayed-code code-font">
|
|
<span class="reserved-syntax">void</span><span class="plain-syntax"> </span><span class="function-syntax">EliminateRedundantLabelsStage::traverse_code_tree</span><button class="popup" onclick="togglePopup('usagePopup2')"><span class="comment-syntax">?</span><span class="popuptext" id="usagePopup2">Usage of <span class="code-font"><span class="function-syntax">EliminateRedundantLabelsStage::traverse_code_tree</span></span>:<br/><a href="6-erls.html#SP1_1_2">§1.1.2</a></span></button><span class="plain-syntax">(</span><span class="identifier-syntax">inter_tree_node</span><span class="plain-syntax"> *</span><span class="identifier-syntax">P</span><span class="plain-syntax">) {</span>
|
|
<span class="plain-syntax"> </span><span class="identifier-syntax">LOOP_THROUGH_INTER_CHILDREN</span><span class="plain-syntax">(</span><span class="identifier-syntax">F</span><span class="plain-syntax">, </span><span class="identifier-syntax">P</span><span class="plain-syntax">) {</span>
|
|
<span class="plain-syntax"> </span><span class="named-paragraph-container code-font"><a href="6-erls.html#SP2_1" class="named-paragraph-link"><span class="named-paragraph">Examine a line of code in the function</span><span class="named-paragraph-number">2.1</span></a></span><span class="plain-syntax">;</span>
|
|
<span class="plain-syntax"> </span><a href="6-erls.html#SP2" class="function-link"><span class="function-syntax">EliminateRedundantLabelsStage::traverse_code_tree</span></a><span class="plain-syntax">(</span><span class="identifier-syntax">F</span><span class="plain-syntax">);</span>
|
|
<span class="plain-syntax"> }</span>
|
|
<span class="plain-syntax">}</span>
|
|
</pre>
|
|
<p class="commentary firstcommentary"><a id="SP2_1" class="paragraph-anchor"></a><b>§2.1. </b>If a label is used, there will be a line reading <span class="extract"><span class="extract-syntax">lab Example</span></span> or similar.
|
|
We look for such lines.
|
|
</p>
|
|
|
|
<p class="commentary"><span class="named-paragraph-container code-font"><span class="named-paragraph-defn">Examine a line of code in the function</span><span class="named-paragraph-number">2.1</span></span><span class="comment-syntax"> =</span>
|
|
</p>
|
|
|
|
<pre class="displayed-code all-displayed-code code-font">
|
|
<span class="plain-syntax"> </span><span class="reserved-syntax">if</span><span class="plain-syntax"> (</span><span class="identifier-syntax">Inode::is</span><span class="plain-syntax">(</span><span class="identifier-syntax">F</span><span class="plain-syntax">, </span><span class="identifier-syntax">LAB_IST</span><span class="plain-syntax">)) {</span>
|
|
<span class="plain-syntax"> </span><span class="identifier-syntax">inter_symbol</span><span class="plain-syntax"> *</span><span class="identifier-syntax">lab</span><span class="plain-syntax"> = </span><span class="identifier-syntax">LabInstruction::label_symbol</span><span class="plain-syntax">(</span><span class="identifier-syntax">F</span><span class="plain-syntax">);</span>
|
|
<span class="plain-syntax"> </span><span class="identifier-syntax">InterSymbol::set_flag</span><span class="plain-syntax">(</span><span class="identifier-syntax">lab</span><span class="plain-syntax">, </span><span class="identifier-syntax">USED_MARK_ISYMF</span><span class="plain-syntax">);</span>
|
|
<span class="plain-syntax"> }</span>
|
|
</pre>
|
|
<ul class="endnotetexts"><li>This code is used in <a href="6-erls.html#SP2">§2</a>.</li></ul>
|
|
<nav role="progress"><div class="progresscontainer">
|
|
<ul class="progressbar"><li class="progressprev"><a href="6-erms.html">❮</a></li><li class="progresschapter"><a href="P-wtmd.html">P</a></li><li class="progresschapter"><a href="1-pm.html">1</a></li><li class="progresschapter"><a href="2-pp.html">2</a></li><li class="progresschapter"><a href="3-ps.html">3</a></li><li class="progresschapter"><a href="4-lbks.html">4</a></li><li class="progresschapter"><a href="5-msms.html">5</a></li><li class="progresscurrentchapter">6</li><li class="progresssection"><a href="6-erms.html">erms</a></li><li class="progresscurrent">erls</li><li class="progresssection"><a href="6-eros.html">eros</a></li><li class="progressnext"><a href="6-eros.html">❯</a></li></ul></div>
|
|
</nav><!--End of weave-->
|
|
|
|
</main>
|
|
</body>
|
|
</html>
|
|
|