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146 lines
7.2 KiB
HTML
146 lines
7.2 KiB
HTML
4 years ago
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<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
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<html>
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<!-- Copyright (C) 1988-2018 Free Software Foundation, Inc.
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Permission is granted to copy, distribute and/or modify this document
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under the terms of the GNU Free Documentation License, Version 1.3 or
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any later version published by the Free Software Foundation; with the
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Invariant Sections being "Funding Free Software", the Front-Cover
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Texts being (a) (see below), and with the Back-Cover Texts being (b)
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(see below). A copy of the license is included in the section entitled
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"GNU Free Documentation License".
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(a) The FSF's Front-Cover Text is:
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A GNU Manual
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(b) The FSF's Back-Cover Text is:
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You have freedom to copy and modify this GNU Manual, like GNU
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funds for GNU development. -->
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<!-- Created by GNU Texinfo 6.4, http://www.gnu.org/software/texinfo/ -->
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<head>
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<title>Comparing ordered poly_ints (GNU Compiler Collection (GCC) Internals)</title>
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<meta name="description" content="Comparing ordered poly_ints (GNU Compiler Collection (GCC) Internals)">
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<meta name="keywords" content="Comparing ordered poly_ints (GNU Compiler Collection (GCC) Internals)">
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<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
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<link href="index.html#Top" rel="start" title="Top">
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<link href="Option-Index.html#Option-Index" rel="index" title="Option Index">
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<link href="index.html#SEC_Contents" rel="contents" title="Table of Contents">
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<link href="Comparisons-involving-poly_005fint.html#Comparisons-involving-poly_005fint" rel="up" title="Comparisons involving poly_int">
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<link href="Checking-for-a-poly_005fint-marker-value.html#Checking-for-a-poly_005fint-marker-value" rel="next" title="Checking for a poly_int marker value">
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<link href="Comparing-potentially_002dunordered-poly_005fints.html#Comparing-potentially_002dunordered-poly_005fints" rel="prev" title="Comparing potentially-unordered poly_ints">
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</style>
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</head>
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<body lang="en">
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<a name="Comparing-ordered-poly_005fints"></a>
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<div class="header">
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<p>
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Next: <a href="Checking-for-a-poly_005fint-marker-value.html#Checking-for-a-poly_005fint-marker-value" accesskey="n" rel="next">Checking for a <code>poly_int</code> marker value</a>, Previous: <a href="Comparing-potentially_002dunordered-poly_005fints.html#Comparing-potentially_002dunordered-poly_005fints" accesskey="p" rel="prev">Comparing potentially-unordered <code>poly_int</code>s</a>, Up: <a href="Comparisons-involving-poly_005fint.html#Comparisons-involving-poly_005fint" accesskey="u" rel="up">Comparisons involving <code>poly_int</code></a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Option-Index.html#Option-Index" title="Index" rel="index">Index</a>]</p>
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</div>
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<hr>
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<a name="Comparing-ordered-poly_005fints-1"></a>
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<h4 class="subsection">10.3.4 Comparing ordered <code>poly_int</code>s</h4>
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<p>In cases where there is a definite link between two <code>poly_int</code>s,
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such as the outer and inner sizes of subregs, we usually require the sizes
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to be ordered by the <code>known_le</code> partial order. <code>poly_int</code> provides
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the following utility functions for ordered values:
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</p>
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<dl compact="compact">
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<dt>‘<samp>ordered_p (<var>a</var>, <var>b</var>)</samp>’</dt>
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<dd><p>Return true if <var>a</var> and <var>b</var> are ordered by the <code>known_le</code>
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partial order.
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</p>
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</dd>
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<dt>‘<samp>ordered_min (<var>a</var>, <var>b</var>)</samp>’</dt>
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<dd><p>Assert that <var>a</var> and <var>b</var> are ordered by <code>known_le</code> and return the
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minimum of the two. When using this function, please add a comment explaining
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why the values are known to be ordered.
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</p>
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</dd>
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<dt>‘<samp>ordered_max (<var>a</var>, <var>b</var>)</samp>’</dt>
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<dd><p>Assert that <var>a</var> and <var>b</var> are ordered by <code>known_le</code> and return the
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maximum of the two. When using this function, please add a comment explaining
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why the values are known to be ordered.
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</p></dd>
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</dl>
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<p>For example, if a subreg has an outer mode of size <var>outer</var> and an
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inner mode of size <var>inner</var>:
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</p>
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<ul>
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<li> the subreg is complete if known_eq (<var>inner</var>, <var>outer</var>)
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</li><li> otherwise, the subreg is paradoxical if known_le (<var>inner</var>, <var>outer</var>)
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</li><li> otherwise, the subreg is partial if known_le (<var>outer</var>, <var>inner</var>)
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</li><li> otherwise, the subreg is ill-formed
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</li></ul>
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<p>Thus the subreg is only valid if
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‘<samp>ordered_p (<var>outer</var>, <var>inner</var>)</samp>’ is true. If this condition
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is already known to be true then:
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</p>
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<ul>
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<li> the subreg is complete if known_eq (<var>inner</var>, <var>outer</var>)
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</li><li> the subreg is paradoxical if maybe_lt (<var>inner</var>, <var>outer</var>)
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</li><li> the subreg is partial if maybe_lt (<var>outer</var>, <var>inner</var>)
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</li></ul>
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<p>with the three conditions being mutually exclusive.
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</p>
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<p>Code that checks whether a subreg is valid would therefore generally
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check whether <code>ordered_p</code> holds (in addition to whatever other
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checks are required for subreg validity). Code that is dealing
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with existing subregs can assert that <code>ordered_p</code> holds
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and use either of the classifications above.
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</p>
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<hr>
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<div class="header">
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<p>
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Next: <a href="Checking-for-a-poly_005fint-marker-value.html#Checking-for-a-poly_005fint-marker-value" accesskey="n" rel="next">Checking for a <code>poly_int</code> marker value</a>, Previous: <a href="Comparing-potentially_002dunordered-poly_005fints.html#Comparing-potentially_002dunordered-poly_005fints" accesskey="p" rel="prev">Comparing potentially-unordered <code>poly_int</code>s</a>, Up: <a href="Comparisons-involving-poly_005fint.html#Comparisons-involving-poly_005fint" accesskey="u" rel="up">Comparisons involving <code>poly_int</code></a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Option-Index.html#Option-Index" title="Index" rel="index">Index</a>]</p>
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</div>
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</body>
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</html>
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