1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
|
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
<!-- Copyright (C) 1988-2023 Free Software Foundation, Inc.
Permission is granted to copy, distribute and/or modify this document
under the terms of the GNU Free Documentation License, Version 1.3 or
any later version published by the Free Software Foundation; with the
Invariant Sections being "Funding Free Software", the Front-Cover
Texts being (a) (see below), and with the Back-Cover Texts being (b)
(see below). A copy of the license is included in the section entitled
"GNU Free Documentation License".
(a) The FSF's Front-Cover Text is:
A GNU Manual
(b) The FSF's Back-Cover Text is:
You have freedom to copy and modify this GNU Manual, like GNU
software. Copies published by the Free Software Foundation raise
funds for GNU development. -->
<!-- Created by GNU Texinfo 5.1, http://www.gnu.org/software/texinfo/ -->
<head>
<title>GNU Compiler Collection (GCC) Internals: Comparing potentially-unordered poly_ints</title>
<meta name="description" content="GNU Compiler Collection (GCC) Internals: Comparing potentially-unordered poly_ints">
<meta name="keywords" content="GNU Compiler Collection (GCC) Internals: Comparing potentially-unordered poly_ints">
<meta name="resource-type" content="document">
<meta name="distribution" content="global">
<meta name="Generator" content="makeinfo">
<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
<link href="index.html#Top" rel="start" title="Top">
<link href="Option-Index.html#Option-Index" rel="index" title="Option Index">
<link href="index.html#SEC_Contents" rel="contents" title="Table of Contents">
<link href="Comparisons-involving-poly_005fint.html#Comparisons-involving-poly_005fint" rel="up" title="Comparisons involving poly_int">
<link href="Comparing-ordered-poly_005fints.html#Comparing-ordered-poly_005fints" rel="next" title="Comparing ordered poly_ints">
<link href="Properties-of-the-poly_005fint-comparisons.html#Properties-of-the-poly_005fint-comparisons" rel="previous" title="Properties of the poly_int comparisons">
<style type="text/css">
<!--
a.summary-letter {text-decoration: none}
blockquote.smallquotation {font-size: smaller}
div.display {margin-left: 3.2em}
div.example {margin-left: 3.2em}
div.indentedblock {margin-left: 3.2em}
div.lisp {margin-left: 3.2em}
div.smalldisplay {margin-left: 3.2em}
div.smallexample {margin-left: 3.2em}
div.smallindentedblock {margin-left: 3.2em; font-size: smaller}
div.smalllisp {margin-left: 3.2em}
kbd {font-style:oblique}
pre.display {font-family: inherit}
pre.format {font-family: inherit}
pre.menu-comment {font-family: serif}
pre.menu-preformatted {font-family: serif}
pre.smalldisplay {font-family: inherit; font-size: smaller}
pre.smallexample {font-size: smaller}
pre.smallformat {font-family: inherit; font-size: smaller}
pre.smalllisp {font-size: smaller}
span.nocodebreak {white-space:nowrap}
span.nolinebreak {white-space:nowrap}
span.roman {font-family:serif; font-weight:normal}
span.sansserif {font-family:sans-serif; font-weight:normal}
ul.no-bullet {list-style: none}
-->
</style>
</head>
<body lang="en" bgcolor="#FFFFFF" text="#000000" link="#0000FF" vlink="#800080" alink="#FF0000">
<a name="Comparing-potentially_002dunordered-poly_005fints"></a>
<div class="header">
<p>
Next: <a href="Comparing-ordered-poly_005fints.html#Comparing-ordered-poly_005fints" accesskey="n" rel="next">Comparing ordered <code>poly_int</code>s</a>, Previous: <a href="Properties-of-the-poly_005fint-comparisons.html#Properties-of-the-poly_005fint-comparisons" accesskey="p" rel="previous">Properties of the <code>poly_int</code> comparisons</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>
</div>
<hr>
<a name="Comparing-potentially_002dunordered-poly_005fints-1"></a>
<h4 class="subsection">10.3.3 Comparing potentially-unordered <code>poly_int</code>s</h4>
<p>In cases where there is no definite link between two <code>poly_int</code>s,
we can usually make a conservatively-correct assumption. For example,
the conservative assumption for alias analysis is that two references
<em>might</em> alias.
</p>
<p>One way of checking whether [<var>begin1</var>, <var>end1</var>) might overlap
[<var>begin2</var>, <var>end2</var>) using the <code>poly_int</code> comparisons is:
</p>
<div class="smallexample">
<pre class="smallexample">maybe_gt (<var>end1</var>, <var>begin2</var>) && maybe_gt (<var>end2</var>, <var>begin1</var>)
</pre></div>
<p>and another (equivalent) way is:
</p>
<div class="smallexample">
<pre class="smallexample">!(known_le (<var>end1</var>, <var>begin2</var>) || known_le (<var>end2</var>, <var>begin1</var>))
</pre></div>
<p>However, in this particular example, it is better to use the range helper
functions instead. See <a href="Range-checks-on-poly_005fints.html#Range-checks-on-poly_005fints">Range checks on <code>poly_int</code>s</a>.
</p>
</body>
</html>
|
