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| 22 | <a href="./Home">MLton 20180207</a>\r |
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| 26 | <h1>PolyEqual</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="PolyEqual">PolyEqual</a> is an optimization pass for the <a href="SSA">SSA</a>\r |
| 32 | <a href="IntermediateLanguage">IntermediateLanguage</a>, invoked from <a href="SSASimplify">SSASimplify</a>.</p></div>\r |
| 33 | </div>\r |
| 34 | </div>\r |
| 35 | <div class="sect1">\r |
| 36 | <h2 id="_description">Description</h2>\r |
| 37 | <div class="sectionbody">\r |
| 38 | <div class="paragraph"><p>This pass implements polymorphic equality.</p></div>\r |
| 39 | </div>\r |
| 40 | </div>\r |
| 41 | <div class="sect1">\r |
| 42 | <h2 id="_implementation">Implementation</h2>\r |
| 43 | <div class="sectionbody">\r |
| 44 | <div class="ulist"><ul>\r |
| 45 | <li>\r |
| 46 | <p>\r |
| 47 | <a href="https://github.com/MLton/mlton/blob/master/mlton/ssa/poly-equal.fun"><span class="monospaced">poly-equal.fun</span></a>\r |
| 48 | </p>\r |
| 49 | </li>\r |
| 50 | </ul></div>\r |
| 51 | </div>\r |
| 52 | </div>\r |
| 53 | <div class="sect1">\r |
| 54 | <h2 id="_details_and_notes">Details and Notes</h2>\r |
| 55 | <div class="sectionbody">\r |
| 56 | <div class="paragraph"><p>For each datatype, tycon, and vector type, it builds and equality\r |
| 57 | function and translates calls to <span class="monospaced">MLton_equal</span> into calls to that\r |
| 58 | function.</p></div>\r |
| 59 | <div class="paragraph"><p>Also generates calls to <span class="monospaced">Word_equal</span>.</p></div>\r |
| 60 | <div class="paragraph"><p>For tuples, it does the equality test inline; i.e., it does not create\r |
| 61 | a separate equality function for each tuple type.</p></div>\r |
| 62 | <div class="paragraph"><p>All equality functions are created only if necessary, i.e., if\r |
| 63 | equality is actually used at a type.</p></div>\r |
| 64 | <div class="paragraph"><p>Optimizations:</p></div>\r |
| 65 | <div class="ulist"><ul>\r |
| 66 | <li>\r |
| 67 | <p>\r |
| 68 | for datatypes that are enumerations, do not build a case dispatch,\r |
| 69 | just use <span class="monospaced">MLton_eq</span>, as the backend will represent these as ints\r |
| 70 | </p>\r |
| 71 | </li>\r |
| 72 | <li>\r |
| 73 | <p>\r |
| 74 | deep equality always does an <span class="monospaced">MLton_eq</span> test first\r |
| 75 | </p>\r |
| 76 | </li>\r |
| 77 | <li>\r |
| 78 | <p>\r |
| 79 | If one argument to <span class="monospaced">=</span> is a constant and the type will get\r |
| 80 | translated to an <span class="monospaced">IntOrPointer</span>, then just use <span class="monospaced">eq</span> instead of the\r |
| 81 | full equality. This is important for implementing code like the\r |
| 82 | following efficiently:\r |
| 83 | </p>\r |
| 84 | <div class="listingblock">\r |
| 85 | <div class="content monospaced">\r |
| 86 | <pre>if x = 0 ... (* where x is of type IntInf.int *)</pre>\r |
| 87 | </div></div>\r |
| 88 | </li>\r |
| 89 | <li>\r |
| 90 | <p>\r |
| 91 | Also convert pointer equality on scalar types to type specific\r |
| 92 | primitives.\r |
| 93 | </p>\r |
| 94 | </li>\r |
| 95 | </ul></div>\r |
| 96 | </div>\r |
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