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<h1 class="title">dfa</h1>
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<li>
<a class="reference reference-toplevel" href="#6" id="56">Imports</a>
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<details open>
<summary><a class="reference reference-toplevel" href="#7" id="57">Types</a></summary>
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<li><a class="reference" href="#ControlFlowGraph" title="ControlFlowGraph = seq[Instr]">ControlFlowGraph</a></li>
<li><a class="reference" href="#Instr" title="Instr = object
case kind*: InstrKind
of goto, fork, loop:
dest*: int
of def, use:
n*: PNode">Instr</a></li>
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goto, loop, fork, def, use">InstrKind</a></li>
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<summary><a class="reference reference-toplevel" href="#12" id="62">Procs</a></summary>
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<ul class="simple nested-toc-section">constructCfg
<li><a class="reference" href="#constructCfg%2CPSym%2CPNode%2CPSym" title="constructCfg(s: PSym; body: PNode; root: PSym): ControlFlowGraph">constructCfg(s: PSym; body: PNode; root: PSym): ControlFlowGraph</a></li>
</ul>
<ul class="simple nested-toc-section">echoCfg
<li><a class="reference" href="#echoCfg%2CControlFlowGraph%2Cint%2Cint" title="echoCfg(c: ControlFlowGraph; start = 0; last = -1)">echoCfg(c: ControlFlowGraph; start = 0; last = -1)</a></li>
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<a href="https://github.com/nim-lang/Nim/tree/devel/compiler/dfa.nim#L1" class="link-seesrc" target="_blank">Source</a>&nbsp;&nbsp;
<a href="https://github.com/nim-lang/Nim/edit/devel/compiler/dfa.nim#L1" class="link-seesrc" target="_blank" >Edit</a>&nbsp;&nbsp;
<div id="tocRoot"></div>
<p class="module-desc"><p>Data flow analysis for Nim. We transform the AST into a linear list of instructions first to make this easier to handle: There are only 3 different branching instructions: 'goto X' is an unconditional goto, 'fork X' is a conditional goto (either the next instruction or 'X' can be taken), 'loop X' is the only jump that jumps back.</p>
<p>Exhaustive case statements are translated so that the last branch is transformed into an 'else' branch. <tt class="docutils literal"><span class="pre">return</span></tt> and <tt class="docutils literal"><span class="pre">break</span></tt> are all covered by 'goto'.</p>
<p>The data structures and algorithms used here are inspired by &quot;A Graph–Free Approach to Data–Flow Analysis&quot; by Markus Mohnen. <a class="reference external" href="https://link.springer.com/content/pdf/10.1007/3-540-45937-5_6.pdf">https://link.springer.com/content/pdf/10.1007/3-540-45937-5_6.pdf</a></p>
</p>
<div class="section" id="6">
<h1><a class="toc-backref" href="#6">Imports</a></h1>
<dl class="item">
<a class="reference external" href="ast.html">ast</a>, <a class="reference external" href="lineinfos.html">lineinfos</a>, <a class="reference external" href="renderer.html">renderer</a>, <a class="reference external" href="aliasanalysis.html">aliasanalysis</a>
</dl>
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<div class="section" id="7">
<h1><a class="toc-backref" href="#7">Types</a></h1>
<dl class="item">
<div id="ControlFlowGraph">
<dt><pre><a href="dfa.html#ControlFlowGraph"><span class="Identifier">ControlFlowGraph</span></a> <span class="Other">=</span> <span class="Identifier">seq</span><span class="Other">[</span><a href="dfa.html#Instr"><span class="Identifier">Instr</span></a><span class="Other">]</span></pre></dt>
<dd>
<a href="https://github.com/nim-lang/Nim/tree/devel/compiler/dfa.nim#L41" class="link-seesrc" target="_blank">Source</a>&nbsp;&nbsp;
<a href="https://github.com/nim-lang/Nim/edit/devel/compiler/dfa.nim#L41" class="link-seesrc" target="_blank" >Edit</a>&nbsp;&nbsp;
</dd>
</div>
<div id="Instr">
<dt><pre><a href="dfa.html#Instr"><span class="Identifier">Instr</span></a> <span class="Other">=</span> <span class="Keyword">object</span>
<span class="Keyword">case</span> <span class="Identifier">kind</span><span class="Operator">*</span><span class="Other">:</span> <a href="dfa.html#InstrKind"><span class="Identifier">InstrKind</span></a>
<span class="Keyword">of</span> <span class="Identifier">goto</span><span class="Other">,</span> <span class="Identifier">fork</span><span class="Other">,</span> <span class="Identifier">loop</span><span class="Other">:</span>
<span class="Identifier">dest</span><span class="Operator">*</span><span class="Other">:</span> <span class="Identifier">int</span>
<span class="Keyword">of</span> <span class="Identifier">def</span><span class="Other">,</span> <span class="Identifier">use</span><span class="Other">:</span>
<span class="Identifier">n</span><span class="Operator">*</span><span class="Other">:</span> <a href="astdef.html#PNode"><span class="Identifier">PNode</span></a></pre></dt>
<dd>
<a href="https://github.com/nim-lang/Nim/tree/devel/compiler/dfa.nim#L35" class="link-seesrc" target="_blank">Source</a>&nbsp;&nbsp;
<a href="https://github.com/nim-lang/Nim/edit/devel/compiler/dfa.nim#L35" class="link-seesrc" target="_blank" >Edit</a>&nbsp;&nbsp;
</dd>
</div>
<div id="InstrKind">
<dt><pre><a href="dfa.html#InstrKind"><span class="Identifier">InstrKind</span></a> <span class="Other">=</span> <span class="Keyword">enum</span>
<span class="Identifier">goto</span><span class="Other">,</span> <span class="Identifier">loop</span><span class="Other">,</span> <span class="Identifier">fork</span><span class="Other">,</span> <span class="Identifier">def</span><span class="Other">,</span> <span class="Identifier">use</span></pre></dt>
<dd>
<a href="https://github.com/nim-lang/Nim/tree/devel/compiler/dfa.nim#L33" class="link-seesrc" target="_blank">Source</a>&nbsp;&nbsp;
<a href="https://github.com/nim-lang/Nim/edit/devel/compiler/dfa.nim#L33" class="link-seesrc" target="_blank" >Edit</a>&nbsp;&nbsp;
</dd>
</div>
</dl>
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<div class="section" id="12">
<h1><a class="toc-backref" href="#12">Procs</a></h1>
<dl class="item">
<div id="constructCfg-procs-all">
<div id="constructCfg,PSym,PNode,PSym">
<dt><pre><span class="Keyword">proc</span> <a href="#constructCfg%2CPSym%2CPNode%2CPSym"><span class="Identifier">constructCfg</span></a><span class="Other">(</span><span class="Identifier">s</span><span class="Other">:</span> <a href="astdef.html#PSym"><span class="Identifier">PSym</span></a><span class="Other">;</span> <span class="Identifier">body</span><span class="Other">:</span> <a href="astdef.html#PNode"><span class="Identifier">PNode</span></a><span class="Other">;</span> <span class="Identifier">root</span><span class="Other">:</span> <a href="astdef.html#PSym"><span class="Identifier">PSym</span></a><span class="Other">)</span><span class="Other">:</span> <a href="dfa.html#ControlFlowGraph"><span class="Identifier">ControlFlowGraph</span></a> {.
<span><span class="Other pragmadots">...</span></span><span class="pragmawrap"><span class="Identifier">raises</span><span class="Other">:</span> <span class="Other">[</span><span class="Identifier">Exception</span><span class="Other">,</span> <span class="Identifier">OSError</span><span class="Other">,</span> <span class="Identifier">KeyError</span><span class="Other">,</span> <span class="Identifier">ValueError</span><span class="Other">,</span> <span class="Identifier">IOError</span><span class="Other">]</span><span class="Other">,</span> <span class="Identifier">tags</span><span class="Other">:</span> <span class="Other">[</span>
<span class="Identifier">RootEffect</span><span class="Other">,</span> <span class="Identifier">WriteIOEffect</span><span class="Other">,</span> <span class="Identifier">ReadEnvEffect</span><span class="Other">,</span> <span class="Identifier">ReadIOEffect</span><span class="Other">,</span> <span class="Identifier">ReadDirEffect</span><span class="Other">]</span><span class="Other">,</span>
<span class="Identifier">forbids</span><span class="Other">:</span> <span class="Other">[</span><span class="Other">]</span></span>.}</pre></dt>
<dd>
constructs a control flow graph for <tt class="docutils literal"><span class="pre">body</span></tt>.
<a href="https://github.com/nim-lang/Nim/tree/devel/compiler/dfa.nim#L479" class="link-seesrc" target="_blank">Source</a>&nbsp;&nbsp;
<a href="https://github.com/nim-lang/Nim/edit/devel/compiler/dfa.nim#L479" class="link-seesrc" target="_blank" >Edit</a>&nbsp;&nbsp;
</dd>
</div>
</div>
<div id="echoCfg-procs-all">
<div id="echoCfg,ControlFlowGraph,int,int">
<dt><pre><span class="Keyword">proc</span> <a href="#echoCfg%2CControlFlowGraph%2Cint%2Cint"><span class="Identifier">echoCfg</span></a><span class="Other">(</span><span class="Identifier">c</span><span class="Other">:</span> <a href="dfa.html#ControlFlowGraph"><span class="Identifier">ControlFlowGraph</span></a><span class="Other">;</span> <span class="Identifier">start</span> <span class="Other">=</span> <span class="DecNumber">0</span><span class="Other">;</span> <span class="Identifier">last</span> <span class="Other">=</span> <span class="DecNumber">-1</span><span class="Other">)</span> {.<span><span class="Other pragmadots">...</span></span><span class="pragmawrap"><span class="Identifier">deprecated</span><span class="Other">,</span>
<span class="Identifier">raises</span><span class="Other">:</span> <span class="Other">[</span><span class="Identifier">Exception</span><span class="Other">,</span> <span class="Identifier">KeyError</span><span class="Other">]</span><span class="Other">,</span> <span class="Identifier">tags</span><span class="Other">:</span> <span class="Other">[</span><span class="Identifier">RootEffect</span><span class="Other">]</span><span class="Other">,</span> <span class="Identifier">forbids</span><span class="Other">:</span> <span class="Other">[</span><span class="Other">]</span></span>.}</pre></dt>
<dd>
<div class="deprecation-message">
<b>Deprecated</b>
</div>
echos the ControlFlowGraph for debugging purposes.
<a href="https://github.com/nim-lang/Nim/tree/devel/compiler/dfa.nim#L88" class="link-seesrc" target="_blank">Source</a>&nbsp;&nbsp;
<a href="https://github.com/nim-lang/Nim/edit/devel/compiler/dfa.nim#L88" class="link-seesrc" target="_blank" >Edit</a>&nbsp;&nbsp;
</dd>
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