HCoop / hcoop / debian / mlton.git / blame
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1 | <!DOCTYPE html>\r |
| 2 | <html lang="en">\r | |
| 3 | <head>\r | |
| 4 | <meta http-equiv="Content-Type" content="text/html; charset=UTF-8">\r | |
| 5 | <meta name="generator" content="AsciiDoc 8.6.9">\r | |
| 6 | <title>Shrink</title>\r | |
| 7 | <link rel="stylesheet" href="./asciidoc.css" type="text/css">\r | |
| 8 | <link rel="stylesheet" href="./pygments.css" type="text/css">\r | |
| 9 | \r | |
| 10 | \r | |
| 11 | <script type="text/javascript" src="./asciidoc.js"></script>\r | |
| 12 | <script type="text/javascript">\r | |
| 13 | /*<![CDATA[*/\r | |
| 14 | asciidoc.install();\r | |
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| 16 | </script>\r | |
| 17 | <link rel="stylesheet" href="./mlton.css" type="text/css">\r | |
| 18 | </head>\r | |
| 19 | <body class="article">\r | |
| 20 | <div id="banner">\r | |
| 21 | <div id="banner-home">\r | |
| 22 | <a href="./Home">MLton 20180207</a>\r | |
| 23 | </div>\r | |
| 24 | </div>\r | |
| 25 | <div id="header">\r | |
| 26 | <h1>Shrink</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="Shrink">Shrink</a> is a rewrite pass for the <a href="SSA">SSA</a> and <a href="SSA2">SSA2</a>\r | |
| 32 | <a href="IntermediateLanguage">IntermediateLanguage</a>s, invoked from every optimization pass (see\r | |
| 33 | <a href="SSASimplify">SSASimplify</a> and <a href="SSA2Simplify">SSA2Simplify</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>This pass implements a whole family of compile-time reductions, like:</p></div>\r | |
| 40 | <div class="ulist"><ul>\r | |
| 41 | <li>\r | |
| 42 | <p>\r | |
| 43 | <span class="monospaced">#1(a, b)</span> ⇒ <span class="monospaced">a</span>\r | |
| 44 | </p>\r | |
| 45 | </li>\r | |
| 46 | <li>\r | |
| 47 | <p>\r | |
| 48 | <span class="monospaced">case C x of C y => e</span> ⇒ <span class="monospaced">let y = x in e</span>\r | |
| 49 | </p>\r | |
| 50 | </li>\r | |
| 51 | <li>\r | |
| 52 | <p>\r | |
| 53 | constant folding, copy propagation\r | |
| 54 | </p>\r | |
| 55 | </li>\r | |
| 56 | <li>\r | |
| 57 | <p>\r | |
| 58 | eta blocks\r | |
| 59 | </p>\r | |
| 60 | </li>\r | |
| 61 | <li>\r | |
| 62 | <p>\r | |
| 63 | tuple reconstruction elimination\r | |
| 64 | </p>\r | |
| 65 | </li>\r | |
| 66 | </ul></div>\r | |
| 67 | </div>\r | |
| 68 | </div>\r | |
| 69 | <div class="sect1">\r | |
| 70 | <h2 id="_implementation">Implementation</h2>\r | |
| 71 | <div class="sectionbody">\r | |
| 72 | <div class="ulist"><ul>\r | |
| 73 | <li>\r | |
| 74 | <p>\r | |
| 75 | <a href="https://github.com/MLton/mlton/blob/master/mlton/ssa/shrink.sig"><span class="monospaced">shrink.sig</span></a>\r | |
| 76 | </p>\r | |
| 77 | </li>\r | |
| 78 | <li>\r | |
| 79 | <p>\r | |
| 80 | <a href="https://github.com/MLton/mlton/blob/master/mlton/ssa/shrink.fun"><span class="monospaced">shrink.fun</span></a>\r | |
| 81 | </p>\r | |
| 82 | </li>\r | |
| 83 | <li>\r | |
| 84 | <p>\r | |
| 85 | <a href="https://github.com/MLton/mlton/blob/master/mlton/ssa/shrink2.sig"><span class="monospaced">shrink2.sig</span></a>\r | |
| 86 | </p>\r | |
| 87 | </li>\r | |
| 88 | <li>\r | |
| 89 | <p>\r | |
| 90 | <a href="https://github.com/MLton/mlton/blob/master/mlton/ssa/shrink2.fun"><span class="monospaced">shrink2.fun</span></a>\r | |
| 91 | </p>\r | |
| 92 | </li>\r | |
| 93 | </ul></div>\r | |
| 94 | </div>\r | |
| 95 | </div>\r | |
| 96 | <div class="sect1">\r | |
| 97 | <h2 id="_details_and_notes">Details and Notes</h2>\r | |
| 98 | <div class="sectionbody">\r | |
| 99 | <div class="paragraph"><p>The <a href="Shrink">Shrink</a> pass is run after every <a href="SSA">SSA</a> and <a href="SSA2">SSA2</a>\r | |
| 100 | optimization pass.</p></div>\r | |
| 101 | <div class="paragraph"><p>The <a href="Shrink">Shrink</a> implementation also includes functions to eliminate\r | |
| 102 | unreachable blocks from a <a href="SSA">SSA</a> or <a href="SSA2">SSA2</a> program or function.\r | |
| 103 | The <a href="Shrink">Shrink</a> pass does not guarantee to eliminate all unreachable\r | |
| 104 | blocks. Doing so would unduly complicate the implementation, and it\r | |
| 105 | is almost always the case that all unreachable blocks are eliminated.\r | |
| 106 | However, a small number of optimization passes require that the input\r | |
| 107 | have no unreachable blocks (essentially, when the analysis works on\r | |
| 108 | the control flow graph and the rewrite iterates on the vector of\r | |
| 109 | blocks). These passes explicitly call <span class="monospaced">eliminateDeadBlocks</span>.</p></div>\r | |
| 110 | <div class="paragraph"><p>The <a href="Shrink">Shrink</a> pass has a special case to turn a non-tail call where\r | |
| 111 | the continuation and handler only do <span class="monospaced">Profile</span> statements into a tail\r | |
| 112 | call where the <span class="monospaced">Profile</span> statements precede the tail call.</p></div>\r | |
| 113 | </div>\r | |
| 114 | </div>\r | |
| 115 | </div>\r | |
| 116 | <div id="footnotes"><hr></div>\r | |
| 117 | <div id="footer">\r | |
| 118 | <div id="footer-text">\r | |
| 119 | </div>\r | |
| 120 | <div id="footer-badges">\r | |
| 121 | </div>\r | |
| 122 | </div>\r | |
| 123 | </body>\r | |
| 124 | </html>\r |