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Import Upstream version 20180207
[hcoop/debian/mlton.git] / doc / guide / localhost / SSA2
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5<meta name="generator" content="AsciiDoc 8.6.9">\r
6<title>SSA2</title>\r
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22<a href="./Home">MLton 20180207</a>\r
23</div>\r
24</div>\r
25<div id="header">\r
26<h1>SSA2</h1>\r
27</div>\r
28<div id="content">\r
29<div id="preamble">\r
30<div class="sectionbody">\r
31<div class="paragraph"><p><a href="SSA2">SSA2</a> is an <a href="IntermediateLanguage">IntermediateLanguage</a>, translated from <a href="SSA">SSA</a> by\r
32<a href="ToSSA2">ToSSA2</a>, optimized by <a href="SSA2Simplify">SSA2Simplify</a>, and translated by\r
33<a href="ToRSSA">ToRSSA</a> to <a href="RSSA">RSSA</a>.</p></div>\r
34</div>\r
35</div>\r
36<div class="sect1">\r
37<h2 id="_description">Description</h2>\r
38<div class="sectionbody">\r
39<div class="paragraph"><p><a href="SSA2">SSA2</a> is a <a href="FirstOrder">FirstOrder</a>, <a href="SimplyTyped">SimplyTyped</a>\r
40<a href="IntermediateLanguage">IntermediateLanguage</a>, a slight variant of the <a href="SSA">SSA</a>\r
41<a href="IntermediateLanguage">IntermediateLanguage</a>,</p></div>\r
42<div class="paragraph"><p>Like <a href="SSA">SSA</a>, an <a href="SSA2">SSA2</a> program consists of a collection of datatype\r
43declarations, a sequence of global statements, and a collection of\r
44functions, along with a distinguished "main" function. Each function\r
45consists of a collection of basic blocks, where each basic block is a\r
46sequence of statements ending with some control transfer.</p></div>\r
47<div class="paragraph"><p>Unlike <a href="SSA">SSA</a>, <a href="SSA2">SSA2</a> includes mutable fields in objects and makes\r
48the vector type constructor n-ary instead of unary. This allows\r
49optimizations like <a href="RefFlatten">RefFlatten</a> and <a href="DeepFlatten">DeepFlatten</a> to be expressed.</p></div>\r
50</div>\r
51</div>\r
52<div class="sect1">\r
53<h2 id="_implementation">Implementation</h2>\r
54<div class="sectionbody">\r
55<div class="ulist"><ul>\r
56<li>\r
57<p>\r
58<a href="https://github.com/MLton/mlton/blob/master/mlton/ssa/ssa2.sig"><span class="monospaced">ssa2.sig</span></a>\r
59</p>\r
60</li>\r
61<li>\r
62<p>\r
63<a href="https://github.com/MLton/mlton/blob/master/mlton/ssa/ssa2.fun"><span class="monospaced">ssa2.fun</span></a>\r
64</p>\r
65</li>\r
66<li>\r
67<p>\r
68<a href="https://github.com/MLton/mlton/blob/master/mlton/ssa/ssa-tree2.sig"><span class="monospaced">ssa-tree2.sig</span></a>\r
69</p>\r
70</li>\r
71<li>\r
72<p>\r
73<a href="https://github.com/MLton/mlton/blob/master/mlton/ssa/ssa-tree2.fun"><span class="monospaced">ssa-tree2.fun</span></a>\r
74</p>\r
75</li>\r
76</ul></div>\r
77</div>\r
78</div>\r
79<div class="sect1">\r
80<h2 id="_type_checking">Type Checking</h2>\r
81<div class="sectionbody">\r
82<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>,\r
83<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>\r
84program verifies the following:</p></div>\r
85<div class="ulist"><ul>\r
86<li>\r
87<p>\r
88no duplicate definitions (tycons, cons, vars, labels, funcs)\r
89</p>\r
90</li>\r
91<li>\r
92<p>\r
93no out of scope references (tycons, cons, vars, labels, funcs)\r
94</p>\r
95</li>\r
96<li>\r
97<p>\r
98variable definitions dominate variable uses\r
99</p>\r
100</li>\r
101<li>\r
102<p>\r
103case transfers are exhaustive and irredundant\r
104</p>\r
105</li>\r
106<li>\r
107<p>\r
108<span class="monospaced">Enter</span>/<span class="monospaced">Leave</span> profile statements match\r
109</p>\r
110</li>\r
111<li>\r
112<p>\r
113"traditional" well-typedness\r
114</p>\r
115</li>\r
116</ul></div>\r
117</div>\r
118</div>\r
119<div class="sect1">\r
120<h2 id="_details_and_notes">Details and Notes</h2>\r
121<div class="sectionbody">\r
122<div class="paragraph"><p>SSA is an abbreviation for Static Single Assignment.</p></div>\r
123</div>\r
124</div>\r
125</div>\r
126<div id="footnotes"><hr></div>\r
127<div id="footer">\r
128<div id="footer-text">\r
129</div>\r
130<div id="footer-badges">\r
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