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<a href="./Home">MLton 20130715</a>
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<h1>SSA2</h1>
</div>
<div id="content">
<div id="preamble">
<div class="sectionbody">
<div class="paragraph"><p><a href="SSA2">SSA2</a> is an <a href="IntermediateLanguage">IntermediateLanguage</a>, translated from <a href="SSA">SSA</a> by
<a href="ToSSA2">ToSSA2</a>, optimized by <a href="SSA2Simplify">SSA2Simplify</a>, and translated by
<a href="ToRSSA">ToRSSA</a> to <a href="RSSA">RSSA</a>.</p></div>
</div>
</div>
<div class="sect1">
<h2 id="_description">Description</h2>
<div class="sectionbody">
<div class="paragraph"><p><a href="SSA2">SSA2</a> is a <a href="FirstOrder">FirstOrder</a>, <a href="SimplyTyped">SimplyTyped</a>
<a href="IntermediateLanguage">IntermediateLanguage</a>, a slight variant of the <a href="SSA">SSA</a>
<a href="IntermediateLanguage">IntermediateLanguage</a>,</p></div>
<div class="paragraph"><p>Like <a href="SSA">SSA</a>, a <a href="SSA">SSA</a> program consists of a collection of datatype
declarations, a sequence of global statements, and a collection of
functions, along with a distinguished "main" function. Each function
consists of a collection of basic blocks, where each basic block is a
sequence of statements ending with some control transfer.</p></div>
<div class="paragraph"><p>Unlike <a href="SSA">SSA</a>, <a href="SSA2">SSA2</a> includes mutable fields in objects and makes
the vector type constructor n-ary instead of unary. This allows
optimizations like <a href="RefFlatten">RefFlatten</a> and <a href="DeepFlatten">DeepFlatten</a> to be expressed.</p></div>
</div>
</div>
<div class="sect1">
<h2 id="_implementation">Implementation</h2>
<div class="sectionbody">
<div class="ulist"><ul>
<li>
<p>
<a href="https://github.com/MLton/mlton/blob/master/mlton/ssa/ssa2.sig"><span class="monospaced">ssa2.sig</span></a>
</p>
</li>
<li>
<p>
<a href="https://github.com/MLton/mlton/blob/master/mlton/ssa/ssa2.fun"><span class="monospaced">ssa2.fun</span></a>
</p>
</li>
<li>
<p>
<a href="https://github.com/MLton/mlton/blob/master/mlton/ssa/ssa-tree2.sig"><span class="monospaced">ssa-tree2.sig</span></a>
</p>
</li>
<li>
<p>
<a href="https://github.com/MLton/mlton/blob/master/mlton/ssa/ssa-tree2.fun"><span class="monospaced">ssa-tree2.fun</span></a>
</p>
</li>
</ul></div>
</div>
</div>
<div class="sect1">
<h2 id="_type_checking">Type Checking</h2>
<div class="sectionbody">
<div class="paragraph"><p>Type checking (<a href="https://github.com/MLton/mlton/blob/master/mlton/ssa/type-check2.sig"><span class="monospaced">type-check2.sig</span></a>,
<a href="https://github.com/MLton/mlton/blob/master/mlton/ssa/type-check2.fun"><span class="monospaced">type-check2.fun</span></a>) of a <a href="SSA2">SSA2</a>
program verifies the following:</p></div>
<div class="ulist"><ul>
<li>
<p>
no duplicate definitions (tycons, cons, vars, labels, funcs)
</p>
</li>
<li>
<p>
no out of scope references (tycons, cons, vars, labels, funcs)
</p>
</li>
<li>
<p>
variable definitions dominate variable uses
</p>
</li>
<li>
<p>
case transfers are exhaustive and irredundant
</p>
</li>
<li>
<p>
<span class="monospaced">Enter</span>/<span class="monospaced">Leave</span> profile statements match
</p>
</li>
<li>
<p>
"traditional" well-typedness
</p>
</li>
</ul></div>
</div>
</div>
<div class="sect1">
<h2 id="_details_and_notes">Details and Notes</h2>
<div class="sectionbody">
<div class="paragraph"><p>SSA is an abbreviation for Static Single Assignment.</p></div>
</div>
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