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<a class = mltona href="Home">MLton 20061025</a>
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SSA2
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SSA2 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>. <h2 id="head-55f8ebc805e65b5b71ddafdae390e3be2bcd69af">Description</h2>
<p>
SSA2 is a <a class="nonexistent" href="FirstOrder">FirstOrder</a>, <a class="nonexistent" 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>
<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.
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<p>
Unlike <a href="SSA">SSA</a>, SSA2 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>
<h2 id="head-8781d615fd77be9578225c40ac67b9471394cced">Implementation</h2>
<a href = "http://mlton.org/cgi-bin/viewsvn.cgi/mlton/tags/on-20061025-release/mlton/ssa/ssa2.sig?view=markup"><img src="moin-www.png" alt="[WWW]" height="11" width="11">ssa2.sig</a>
<a href = "http://mlton.org/cgi-bin/viewsvn.cgi/mlton/tags/on-20061025-release/mlton/ssa/ssa2.fun?view=markup"><img src="moin-www.png" alt="[WWW]" height="11" width="11">ssa2.fun</a>
<br>
<a href = "http://mlton.org/cgi-bin/viewsvn.cgi/mlton/tags/on-20061025-release/mlton/ssa/ssa-tree2.sig?view=markup"><img src="moin-www.png" alt="[WWW]" height="11" width="11">ssa-tree2.sig</a>
<a href = "http://mlton.org/cgi-bin/viewsvn.cgi/mlton/tags/on-20061025-release/mlton/ssa/ssa-tree2.fun?view=markup"><img src="moin-www.png" alt="[WWW]" height="11" width="11">ssa-tree2.fun</a>
<h2 id="head-a6de4b535fedeaa8890bd890b60fe09f87b5f96a">Type Checking</h2>
<p>
Type checking of a SSA2 program verfies the following:
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<p>
no duplicate definitions (tycons, cons, vars, labels, funcs)
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<p>
no out of scope references (tycons, cons, vars, labels, funcs)
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</li>
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<p>
variable definitions dominate variable uses
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</li>
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<p>
case transfers are exhaustive and irredundant
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</li>
<li>
<p>
<tt>Enter</tt>/<tt>Leave</tt> profile statements match
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<li>
<p>
"traditional" well-typedness
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<p>
<a href = "http://mlton.org/cgi-bin/viewsvn.cgi/mlton/tags/on-20061025-release/mlton/ssa/type-check2.sig?view=markup"><img src="moin-www.png" alt="[WWW]" height="11" width="11">type-check2.sig</a>
<a href = "http://mlton.org/cgi-bin/viewsvn.cgi/mlton/tags/on-20061025-release/mlton/ssa/type-check2.fun?view=markup"><img src="moin-www.png" alt="[WWW]" height="11" width="11">type-check2.fun</a>
</p>
<h2 id="head-35ec00231a68203708e39f0e2cc10b50c6bf62de">Details and Notes</h2>
<p>
SSA is an abbreviation for Static Single Assignment.
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<p>
<hr>
Last edited on 2005-12-02 03:19:44 by <span title="ppp-71-139-183-221.dsl.snfc21.pacbell.net"><a href="StephenWeeks">StephenWeeks</a></span>.
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