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128 lines
7.5 KiB
HTML
128 lines
7.5 KiB
HTML
4 years ago
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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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<!-- Created by GNU Texinfo 6.4, http://www.gnu.org/software/texinfo/ -->
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<head>
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<title>Comparisons involving poly_int (GNU Compiler Collection (GCC) Internals)</title>
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<meta name="description" content="Comparisons involving poly_int (GNU Compiler Collection (GCC) Internals)">
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<meta name="keywords" content="Comparisons involving poly_int (GNU Compiler Collection (GCC) Internals)">
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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="poly_005fint.html#poly_005fint" rel="up" title="poly_int">
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<link href="Comparison-functions-for-poly_005fint.html#Comparison-functions-for-poly_005fint" rel="next" title="Comparison functions for poly_int">
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<link href="Consequences-of-using-poly_005fint.html#Consequences-of-using-poly_005fint" rel="prev" title="Consequences of using poly_int">
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</head>
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<body lang="en">
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<a name="Comparisons-involving-poly_005fint"></a>
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<div class="header">
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<p>
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Next: <a href="Arithmetic-on-poly_005fints.html#Arithmetic-on-poly_005fints" accesskey="n" rel="next">Arithmetic on <code>poly_int</code>s</a>, Previous: <a href="Consequences-of-using-poly_005fint.html#Consequences-of-using-poly_005fint" accesskey="p" rel="prev">Consequences of using <code>poly_int</code></a>, Up: <a href="poly_005fint.html#poly_005fint" accesskey="u" rel="up">poly_int</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="Comparisons-involving-poly_005fint-1"></a>
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<h3 class="section">10.3 Comparisons involving <code>poly_int</code></h3>
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<p>In general we need to compare sizes and offsets in two situations:
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those in which the values need to be ordered, and those in which
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the values can be unordered. More loosely, the distinction is often
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between values that have a definite link (usually because they refer to the
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same underlying register or memory location) and values that have
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no definite link. An example of the former is the relationship between
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the inner and outer sizes of a subreg, where we must know at compile time
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whether the subreg is paradoxical, partial, or complete. An example of
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the latter is alias analysis: we might want to check whether two
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arbitrary memory references overlap.
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</p>
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<p>Referring back to the examples in the previous section, it makes sense
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to ask whether a memory reference of size ‘<samp>3 + 4<var>x</var></samp>’ overlaps
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one of size ‘<samp>1 + 5<var>x</var></samp>’, but it does not make sense to have a
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subreg in which the outer mode has ‘<samp>3 + 4<var>x</var></samp>’ bytes and the
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inner mode has ‘<samp>1 + 5<var>x</var></samp>’ bytes (or vice versa). Such subregs
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are always invalid and should trigger an internal compiler error
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if formed.
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</p>
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<p>The underlying operators are the same in both cases, but the distinction
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affects how they are used.
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</p>
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<table class="menu" border="0" cellspacing="0">
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<tr><td align="left" valign="top">• <a href="Comparison-functions-for-poly_005fint.html#Comparison-functions-for-poly_005fint" accesskey="1">Comparison functions for <code>poly_int</code></a>:</td><td> </td><td align="left" valign="top">
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</td></tr>
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<tr><td align="left" valign="top">• <a href="Properties-of-the-poly_005fint-comparisons.html#Properties-of-the-poly_005fint-comparisons" accesskey="2">Properties of the <code>poly_int</code> comparisons</a>:</td><td> </td><td align="left" valign="top">
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</td></tr>
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<tr><td align="left" valign="top">• <a href="Comparing-potentially_002dunordered-poly_005fints.html#Comparing-potentially_002dunordered-poly_005fints" accesskey="3">Comparing potentially-unordered <code>poly_int</code>s</a>:</td><td> </td><td align="left" valign="top">
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</td></tr>
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<tr><td align="left" valign="top">• <a href="Comparing-ordered-poly_005fints.html#Comparing-ordered-poly_005fints" accesskey="4">Comparing ordered <code>poly_int</code>s</a>:</td><td> </td><td align="left" valign="top">
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</td></tr>
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<tr><td align="left" valign="top">• <a href="Checking-for-a-poly_005fint-marker-value.html#Checking-for-a-poly_005fint-marker-value" accesskey="5">Checking for a <code>poly_int</code> marker value</a>:</td><td> </td><td align="left" valign="top">
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</td></tr>
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<tr><td align="left" valign="top">• <a href="Range-checks-on-poly_005fints.html#Range-checks-on-poly_005fints" accesskey="6">Range checks on <code>poly_int</code>s</a>:</td><td> </td><td align="left" valign="top">
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</td></tr>
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<tr><td align="left" valign="top">• <a href="Sorting-poly_005fints.html#Sorting-poly_005fints" accesskey="7">Sorting <code>poly_int</code>s</a>:</td><td> </td><td align="left" valign="top">
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</td></tr>
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</table>
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<hr>
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<div class="header">
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<p>
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Next: <a href="Arithmetic-on-poly_005fints.html#Arithmetic-on-poly_005fints" accesskey="n" rel="next">Arithmetic on <code>poly_int</code>s</a>, Previous: <a href="Consequences-of-using-poly_005fint.html#Consequences-of-using-poly_005fint" accesskey="p" rel="prev">Consequences of using <code>poly_int</code></a>, Up: <a href="poly_005fint.html#poly_005fint" accesskey="u" rel="up">poly_int</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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