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194 lines
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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
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<html>
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<head>
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<title>2/rv</title>
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<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
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<meta http-equiv="Content-Language" content="en-gb">
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<link href="inweb.css" rel="stylesheet" rev="stylesheet" type="text/css">
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</head>
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<body>
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<!--Weave of '2/erm' generated by 7-->
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<ul class="crumbs"><li><a href="../webs.html">★</a></li><li><a href="index.html">codegen</a></li><li><a href="index.html#2">Chapter 2: Miscellaneous Pipeline Stages</a></li><li><b>Eliminate Redundant Matter</b></li></ul><p class="purpose">To remove (for example) functions which we can prove will never be called or referred to as values.</p>
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<ul class="toc"><li><a href="#SP1">§1. Pipeline stage</a></li><li><a href="#SP2">§2. Preservation</a></li><li><a href="#SP4">§4. Destruction</a></li></ul><hr class="tocbar">
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<p class="inwebparagraph"><a id="SP1"></a><b>§1. Pipeline stage. </b>Experience shows that around 20 per cent of the code generated by Inform 7
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consists of functions which are never in fact needed. Probably diligent
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book-keeping at the generation stage could reduce some of that, but other
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redundancies arise because of functions assimilated from the template, and
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we don't have much control over that. This stage removes everything that
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isn't used.
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</p>
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<pre class="display">
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<span class="reserved">void</span><span class="plain"> </span><span class="functiontext">CodeGen::Eliminate::create_pipeline_stage</span><span class="plain">(</span><span class="reserved">void</span><span class="plain">) {</span>
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<span class="functiontext">CodeGen::Stage::new</span><span class="plain">(</span><span class="identifier">I</span><span class="string">"eliminate-redundant-code"</span><span class="plain">,</span>
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<span class="functiontext">CodeGen::Eliminate::run_pipeline_stage</span><span class="plain">, </span><span class="constant">NO_STAGE_ARG</span><span class="plain">, </span><span class="identifier">FALSE</span><span class="plain">);</span>
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<span class="plain">}</span>
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<span class="reserved">int</span><span class="plain"> </span><span class="functiontext">CodeGen::Eliminate::run_pipeline_stage</span><span class="plain">(</span><span class="reserved">pipeline_step</span><span class="plain"> *</span><span class="identifier">step</span><span class="plain">) {</span>
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<span class="identifier">inter_tree</span><span class="plain"> *</span><span class="identifier">I</span><span class="plain"> = </span><span class="identifier">step</span><span class="plain">-</span><span class="element">>repository</span><span class="plain">;</span>
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<span class="identifier">Inter::Tree::traverse</span><span class="plain">(</span><span class="identifier">I</span><span class="plain">, </span><span class="functiontext">CodeGen::Eliminate::package_preserver</span><span class="plain">, </span><span class="identifier">NULL</span><span class="plain">, </span><span class="identifier">NULL</span><span class="plain">, </span><span class="identifier">PACKAGE_IST</span><span class="plain">);</span>
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<span class="identifier">Inter::Tree::traverse</span><span class="plain">(</span><span class="identifier">I</span><span class="plain">, </span><span class="functiontext">CodeGen::Eliminate::package_destroyer</span><span class="plain">, </span><span class="identifier">NULL</span><span class="plain">, </span><span class="identifier">NULL</span><span class="plain">, </span><span class="identifier">PACKAGE_IST</span><span class="plain">);</span>
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<span class="reserved">return</span><span class="plain"> </span><span class="identifier">TRUE</span><span class="plain">;</span>
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<span class="plain">}</span>
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</pre>
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<p class="inwebparagraph"></p>
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<p class="endnote">The function CodeGen::Eliminate::create_pipeline_stage is used in 1/stg (<a href="1-stg.html#SP2">§2</a>).</p>
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<p class="endnote">The function CodeGen::Eliminate::run_pipeline_stage appears nowhere else.</p>
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<p class="inwebparagraph"><a id="SP2"></a><b>§2. Preservation. </b>We operate on a presumption of guilt: any package which we cannot prove is
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needed will be deleted. <code class="display"><span class="extract">Main_fn</span></code> is clearly needed, since it is where
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execution will begin. A handful of other functions, not called yet but
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needed in the final compilation stage (and which replace stubs which would
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otherwise be provided by the veneer), must also be included. Command
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packages contain grammar for command verbs typed at run-time: these affect
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an essential data structure (i.e., the parser grammar) implicitly, and so
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we can't detect the dependency here. So we require all command packages to
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be included.
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</p>
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<pre class="display">
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<span class="reserved">void</span><span class="plain"> </span><span class="functiontext">CodeGen::Eliminate::package_preserver</span><span class="plain">(</span><span class="identifier">inter_tree</span><span class="plain"> *</span><span class="identifier">I</span><span class="plain">, </span><span class="identifier">inter_tree_node</span><span class="plain"> *</span><span class="identifier">P</span><span class="plain">, </span><span class="reserved">void</span><span class="plain"> *</span><span class="identifier">state</span><span class="plain">) {</span>
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<span class="identifier">inter_package</span><span class="plain"> *</span><span class="identifier">pack</span><span class="plain"> = </span><span class="identifier">Inter::Package::defined_by_frame</span><span class="plain">(</span><span class="identifier">P</span><span class="plain">);</span>
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<span class="identifier">inter_symbol</span><span class="plain"> *</span><span class="identifier">ptype</span><span class="plain"> = </span><span class="identifier">Inter::Packages::type</span><span class="plain">(</span><span class="identifier">pack</span><span class="plain">);</span>
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<span class="reserved">if</span><span class="plain"> (</span><span class="identifier">ptype</span><span class="plain"> == </span><span class="identifier">command_ptype_symbol</span><span class="plain">)</span>
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<span class="functiontext">CodeGen::Eliminate::require</span><span class="plain">(</span><span class="identifier">pack</span><span class="plain">, </span><span class="identifier">NULL</span><span class="plain">, </span><span class="identifier">I</span><span class="string">"it's a _command package"</span><span class="plain">);</span>
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<span class="reserved">else</span><span class="plain"> </span><span class="reserved">if</span><span class="plain"> (</span><span class="identifier">ptype</span><span class="plain"> == </span><span class="identifier">property_ptype_symbol</span><span class="plain">)</span>
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<span class="functiontext">CodeGen::Eliminate::require</span><span class="plain">(</span><span class="identifier">pack</span><span class="plain">, </span><span class="identifier">NULL</span><span class="plain">, </span><span class="identifier">I</span><span class="string">"it's a _property package"</span><span class="plain">);</span>
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<span class="reserved">else</span><span class="plain"> </span><span class="reserved">if</span><span class="plain"> (</span><span class="identifier">ptype</span><span class="plain"> == </span><span class="identifier">function_ptype_symbol</span><span class="plain">) {</span>
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<span class="identifier">text_stream</span><span class="plain"> *</span><span class="identifier">N</span><span class="plain"> = </span><span class="identifier">Inter::Packages::name</span><span class="plain">(</span><span class="identifier">pack</span><span class="plain">);</span>
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<span class="reserved">if</span><span class="plain"> (</span><span class="identifier">Str::eq</span><span class="plain">(</span><span class="identifier">N</span><span class="plain">, </span><span class="identifier">I</span><span class="string">"Main_fn"</span><span class="plain">))</span>
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<span class="functiontext">CodeGen::Eliminate::require</span><span class="plain">(</span><span class="identifier">pack</span><span class="plain">, </span><span class="identifier">NULL</span><span class="plain">, </span><span class="identifier">I</span><span class="string">"it's Main"</span><span class="plain">);</span>
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<span class="reserved">else</span><span class="plain"> </span><span class="reserved">if</span><span class="plain"> (</span><span class="identifier">Str::eq</span><span class="plain">(</span><span class="identifier">N</span><span class="plain">, </span><span class="identifier">I</span><span class="string">"DefArt_fn"</span><span class="plain">))</span>
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<span class="functiontext">CodeGen::Eliminate::require</span><span class="plain">(</span><span class="identifier">pack</span><span class="plain">, </span><span class="identifier">NULL</span><span class="plain">, </span><span class="identifier">I</span><span class="string">"it's a veneer replacement"</span><span class="plain">);</span>
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<span class="reserved">else</span><span class="plain"> </span><span class="reserved">if</span><span class="plain"> (</span><span class="identifier">Str::eq</span><span class="plain">(</span><span class="identifier">N</span><span class="plain">, </span><span class="identifier">I</span><span class="string">"CDefArt_fn"</span><span class="plain">))</span>
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<span class="functiontext">CodeGen::Eliminate::require</span><span class="plain">(</span><span class="identifier">pack</span><span class="plain">, </span><span class="identifier">NULL</span><span class="plain">, </span><span class="identifier">I</span><span class="string">"it's a veneer replacement"</span><span class="plain">);</span>
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<span class="reserved">else</span><span class="plain"> </span><span class="reserved">if</span><span class="plain"> (</span><span class="identifier">Str::eq</span><span class="plain">(</span><span class="identifier">N</span><span class="plain">, </span><span class="identifier">I</span><span class="string">"IndefArt_fn"</span><span class="plain">))</span>
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<span class="functiontext">CodeGen::Eliminate::require</span><span class="plain">(</span><span class="identifier">pack</span><span class="plain">, </span><span class="identifier">NULL</span><span class="plain">, </span><span class="identifier">I</span><span class="string">"it's a veneer replacement"</span><span class="plain">);</span>
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<span class="reserved">else</span><span class="plain"> </span><span class="reserved">if</span><span class="plain"> (</span><span class="identifier">Str::eq</span><span class="plain">(</span><span class="identifier">N</span><span class="plain">, </span><span class="identifier">I</span><span class="string">"CIndefArt_fn"</span><span class="plain">))</span>
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<span class="functiontext">CodeGen::Eliminate::require</span><span class="plain">(</span><span class="identifier">pack</span><span class="plain">, </span><span class="identifier">NULL</span><span class="plain">, </span><span class="identifier">I</span><span class="string">"it's a veneer replacement"</span><span class="plain">);</span>
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<span class="plain">}</span>
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<span class="plain">}</span>
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</pre>
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<p class="inwebparagraph"></p>
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<p class="endnote">The function CodeGen::Eliminate::package_preserver is used in <a href="#SP1">§1</a>.</p>
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<p class="inwebparagraph"><a id="SP3"></a><b>§3. </b>Once you need a package, what else do you need?
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</p>
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<pre class="display">
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<span class="reserved">void</span><span class="plain"> </span><span class="functiontext">CodeGen::Eliminate::require</span><span class="plain">(</span><span class="identifier">inter_package</span><span class="plain"> *</span><span class="identifier">pack</span><span class="plain">, </span><span class="identifier">inter_package</span><span class="plain"> *</span><span class="identifier">witness</span><span class="plain">, </span><span class="identifier">text_stream</span><span class="plain"> *</span><span class="identifier">reason</span><span class="plain">) {</span>
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<span class="reserved">if</span><span class="plain"> ((</span><span class="identifier">pack</span><span class="plain">-></span><span class="identifier">package_flags</span><span class="plain">) & </span><span class="identifier">USED_PACKAGE_FLAG</span><span class="plain">) </span><span class="reserved">return</span><span class="plain">;</span>
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<span class="identifier">pack</span><span class="plain">-></span><span class="identifier">package_flags</span><span class="plain"> |= </span><span class="identifier">USED_PACKAGE_FLAG</span><span class="plain">;</span>
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<span class="reserved">if</span><span class="plain"> (</span><span class="identifier">witness</span><span class="plain">) {</span>
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<span class="identifier">LOGIF</span><span class="plain">(</span><span class="identifier">ELIMINATION</span><span class="plain">, </span><span class="string">"Need $6 because of $6 (because %S)\</span><span class="plain">n</span><span class="string">"</span><span class="plain">, </span><span class="identifier">pack</span><span class="plain">, </span><span class="identifier">witness</span><span class="plain">, </span><span class="identifier">reason</span><span class="plain">);</span>
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<span class="plain">} </span><span class="reserved">else</span><span class="plain"> {</span>
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<span class="identifier">LOGIF</span><span class="plain">(</span><span class="identifier">ELIMINATION</span><span class="plain">, </span><span class="string">"Need $6 (because %S)\</span><span class="plain">n</span><span class="string">"</span><span class="plain">, </span><span class="identifier">pack</span><span class="plain">, </span><span class="identifier">reason</span><span class="plain">);</span>
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<span class="plain">}</span>
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<<span class="cwebmacro">If you need a package, you need its parent</span> <span class="cwebmacronumber">3.1</span>><span class="plain">;</span>
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<<span class="cwebmacro">If you need a package, you need its external dependencies</span> <span class="cwebmacronumber">3.2</span>><span class="plain">;</span>
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<<span class="cwebmacro">If you need a function or action, you need its internal resources</span> <span class="cwebmacronumber">3.3</span>><span class="plain">;</span>
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<span class="plain">}</span>
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</pre>
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<p class="inwebparagraph"></p>
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<p class="endnote">The function CodeGen::Eliminate::require is used in <a href="#SP2">§2</a>, <a href="#SP3_1">§3.1</a>, <a href="#SP3_2">§3.2</a>, <a href="#SP3_3">§3.3</a>.</p>
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<p class="inwebparagraph"><a id="SP3_1"></a><b>§3.1. </b><code class="display">
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<<span class="cwebmacrodefn">If you need a package, you need its parent</span> <span class="cwebmacronumber">3.1</span>> =
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</code></p>
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<pre class="displaydefn">
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<span class="identifier">inter_package</span><span class="plain"> *</span><span class="identifier">parent</span><span class="plain"> = </span><span class="identifier">Inter::Packages::parent</span><span class="plain">(</span><span class="identifier">pack</span><span class="plain">);</span>
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<span class="reserved">if</span><span class="plain"> (</span><span class="identifier">parent</span><span class="plain">) </span><span class="functiontext">CodeGen::Eliminate::require</span><span class="plain">(</span><span class="identifier">parent</span><span class="plain">, </span><span class="identifier">pack</span><span class="plain">, </span><span class="identifier">I</span><span class="string">"it's the parent"</span><span class="plain">);</span>
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</pre>
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<p class="inwebparagraph"></p>
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<p class="endnote">This code is used in <a href="#SP3">§3</a>.</p>
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<p class="inwebparagraph"><a id="SP3_2"></a><b>§3.2. </b><code class="display">
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<<span class="cwebmacrodefn">If you need a package, you need its external dependencies</span> <span class="cwebmacronumber">3.2</span>> =
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</code></p>
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<pre class="displaydefn">
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<span class="identifier">inter_symbols_table</span><span class="plain"> *</span><span class="identifier">tab</span><span class="plain"> = </span><span class="identifier">Inter::Packages::scope</span><span class="plain">(</span><span class="identifier">pack</span><span class="plain">);</span>
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<span class="reserved">for</span><span class="plain"> (</span><span class="reserved">int</span><span class="plain"> </span><span class="identifier">i</span><span class="plain">=0; </span><span class="identifier">i</span><span class="plain"><</span><span class="identifier">tab</span><span class="plain">-></span><span class="identifier">size</span><span class="plain">; </span><span class="identifier">i</span><span class="plain">++) {</span>
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<span class="identifier">inter_symbol</span><span class="plain"> *</span><span class="identifier">symb</span><span class="plain"> = </span><span class="identifier">tab</span><span class="plain">-></span><span class="identifier">symbol_array</span><span class="plain">[</span><span class="identifier">i</span><span class="plain">];</span>
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<span class="reserved">if</span><span class="plain"> ((</span><span class="identifier">symb</span><span class="plain">) && (</span><span class="identifier">symb</span><span class="plain">-></span><span class="identifier">equated_to</span><span class="plain">)) {</span>
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<span class="identifier">inter_symbol</span><span class="plain"> *</span><span class="identifier">to</span><span class="plain"> = </span><span class="identifier">symb</span><span class="plain">;</span>
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<span class="reserved">while</span><span class="plain"> ((</span><span class="identifier">to</span><span class="plain">) && (</span><span class="identifier">to</span><span class="plain">-></span><span class="identifier">equated_to</span><span class="plain">)) </span><span class="identifier">to</span><span class="plain"> = </span><span class="identifier">to</span><span class="plain">-></span><span class="identifier">equated_to</span><span class="plain">;</span>
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<span class="identifier">inter_package</span><span class="plain"> *</span><span class="identifier">needed</span><span class="plain"> = </span><span class="identifier">to</span><span class="plain">-></span><span class="identifier">owning_table</span><span class="plain">-></span><span class="identifier">owning_package</span><span class="plain">;</span>
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<span class="functiontext">CodeGen::Eliminate::require</span><span class="plain">(</span><span class="identifier">needed</span><span class="plain">, </span><span class="identifier">pack</span><span class="plain">, </span><span class="identifier">I</span><span class="string">"it's an external symbol"</span><span class="plain">);</span>
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<span class="plain">}</span>
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<span class="plain">}</span>
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</pre>
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<p class="inwebparagraph"></p>
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<p class="endnote">This code is used in <a href="#SP3">§3</a>.</p>
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<p class="inwebparagraph"><a id="SP3_3"></a><b>§3.3. </b><code class="display">
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<<span class="cwebmacrodefn">If you need a function or action, you need its internal resources</span> <span class="cwebmacronumber">3.3</span>> =
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</code></p>
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<pre class="displaydefn">
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<span class="identifier">text_stream</span><span class="plain"> *</span><span class="identifier">rationale</span><span class="plain"> = </span><span class="identifier">NULL</span><span class="plain">;</span>
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<span class="identifier">inter_symbol</span><span class="plain"> *</span><span class="identifier">ptype</span><span class="plain"> = </span><span class="identifier">Inter::Packages::type</span><span class="plain">(</span><span class="identifier">pack</span><span class="plain">);</span>
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<span class="reserved">if</span><span class="plain"> (</span><span class="identifier">ptype</span><span class="plain"> == </span><span class="identifier">function_ptype_symbol</span><span class="plain">) </span><span class="identifier">rationale</span><span class="plain"> = </span><span class="identifier">I</span><span class="string">"it's a _function block"</span><span class="plain">;</span>
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<span class="reserved">if</span><span class="plain"> (</span><span class="identifier">ptype</span><span class="plain"> == </span><span class="identifier">action_ptype_symbol</span><span class="plain">) </span><span class="identifier">rationale</span><span class="plain"> = </span><span class="identifier">I</span><span class="string">"it's an _action subpackage"</span><span class="plain">;</span>
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<span class="reserved">if</span><span class="plain"> (</span><span class="identifier">rationale</span><span class="plain">) {</span>
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<span class="identifier">inter_tree_node</span><span class="plain"> *</span><span class="identifier">D</span><span class="plain"> = </span><span class="identifier">Inter::Packages::definition</span><span class="plain">(</span><span class="identifier">pack</span><span class="plain">);</span>
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<span class="identifier">LOOP_THROUGH_INTER_CHILDREN</span><span class="plain">(</span><span class="identifier">C</span><span class="plain">, </span><span class="identifier">D</span><span class="plain">) {</span>
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<span class="reserved">if</span><span class="plain"> (</span><span class="identifier">C</span><span class="plain">-></span><span class="identifier">W</span><span class="plain">.</span><span class="identifier">data</span><span class="plain">[</span><span class="identifier">ID_IFLD</span><span class="plain">] == </span><span class="identifier">PACKAGE_IST</span><span class="plain">) {</span>
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<span class="identifier">inter_package</span><span class="plain"> *</span><span class="identifier">P</span><span class="plain"> = </span><span class="identifier">Inter::Package::defined_by_frame</span><span class="plain">(</span><span class="identifier">C</span><span class="plain">);</span>
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<span class="functiontext">CodeGen::Eliminate::require</span><span class="plain">(</span><span class="identifier">P</span><span class="plain">, </span><span class="identifier">pack</span><span class="plain">, </span><span class="identifier">rationale</span><span class="plain">);</span>
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<span class="plain">}</span>
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<span class="plain">}</span>
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<span class="plain">}</span>
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</pre>
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<p class="inwebparagraph"></p>
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<p class="endnote">This code is used in <a href="#SP3">§3</a>.</p>
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<p class="inwebparagraph"><a id="SP4"></a><b>§4. Destruction. </b>Whatever has not been preserved, is now destroyed.
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</p>
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<pre class="display">
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<span class="reserved">void</span><span class="plain"> </span><span class="functiontext">CodeGen::Eliminate::package_destroyer</span><span class="plain">(</span><span class="identifier">inter_tree</span><span class="plain"> *</span><span class="identifier">I</span><span class="plain">, </span><span class="identifier">inter_tree_node</span><span class="plain"> *</span><span class="identifier">P</span><span class="plain">, </span><span class="reserved">void</span><span class="plain"> *</span><span class="identifier">state</span><span class="plain">) {</span>
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<span class="identifier">inter_package</span><span class="plain"> *</span><span class="identifier">pack</span><span class="plain"> = </span><span class="identifier">Inter::Package::defined_by_frame</span><span class="plain">(</span><span class="identifier">P</span><span class="plain">);</span>
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<span class="reserved">if</span><span class="plain"> ((</span><span class="identifier">pack</span><span class="plain">) && ((</span><span class="identifier">pack</span><span class="plain">-></span><span class="identifier">package_flags</span><span class="plain"> & </span><span class="identifier">USED_PACKAGE_FLAG</span><span class="plain">) == 0)) {</span>
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<span class="identifier">LOGIF</span><span class="plain">(</span><span class="identifier">ELIMINATION</span><span class="plain">, </span><span class="string">"Striking unused package $6 (type %S)\</span><span class="plain">n</span><span class="string">"</span><span class="plain">,</span>
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<span class="identifier">pack</span><span class="plain">, </span><span class="identifier">Inter::Packages::type</span><span class="plain">(</span><span class="identifier">pack</span><span class="plain">)-></span><span class="identifier">symbol_name</span><span class="plain">);</span>
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<span class="identifier">Inter::Tree::remove_node</span><span class="plain">(</span><span class="identifier">P</span><span class="plain">);</span>
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<span class="plain">}</span>
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<span class="plain">}</span>
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</pre>
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<p class="inwebparagraph"></p>
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<p class="endnote">The function CodeGen::Eliminate::package_destroyer is used in <a href="#SP1">§1</a>.</p>
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<hr class="tocbar">
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<ul class="toc"><li><a href="2-rv.html">Back to 'Reconcile Verbs'</a></li><li><a href="2-erl.html">Continue with 'Eliminate Redundant Labels'</a></li></ul><hr class="tocbar">
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<!--End of weave-->
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