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323 lines
15 KiB
HTML
323 lines
15 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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software. Copies published by the Free Software Foundation raise
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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>Expressions (GNU Compiler Collection (GCC) Internals)</title>
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<meta name="description" content="Expressions (GNU Compiler Collection (GCC) Internals)">
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<meta name="keywords" content="Expressions (GNU Compiler Collection (GCC) Internals)">
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<meta name="resource-type" content="document">
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<meta name="distribution" content="global">
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<meta name="Generator" content="makeinfo">
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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="Insn-Attributes.html#Insn-Attributes" rel="up" title="Insn Attributes">
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<link href="Tagging-Insns.html#Tagging-Insns" rel="next" title="Tagging Insns">
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<link href="Defining-Attributes.html#Defining-Attributes" rel="prev" title="Defining Attributes">
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<style type="text/css">
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a.summary-letter {text-decoration: none}
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div.display {margin-left: 3.2em}
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div.example {margin-left: 3.2em}
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div.lisp {margin-left: 3.2em}
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div.smalldisplay {margin-left: 3.2em}
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kbd {font-style: oblique}
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</style>
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</head>
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<body lang="en">
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<a name="Expressions"></a>
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<div class="header">
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<p>
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Next: <a href="Tagging-Insns.html#Tagging-Insns" accesskey="n" rel="next">Tagging Insns</a>, Previous: <a href="Defining-Attributes.html#Defining-Attributes" accesskey="p" rel="prev">Defining Attributes</a>, Up: <a href="Insn-Attributes.html#Insn-Attributes" accesskey="u" rel="up">Insn Attributes</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="Attribute-Expressions"></a>
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<h4 class="subsection">17.19.2 Attribute Expressions</h4>
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<a name="index-attribute-expressions"></a>
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<p>RTL expressions used to define attributes use the codes described above
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plus a few specific to attribute definitions, to be discussed below.
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Attribute value expressions must have one of the following forms:
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</p>
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<dl compact="compact">
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<dd><a name="index-const_005fint-and-attributes"></a>
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</dd>
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<dt><code>(const_int <var>i</var>)</code></dt>
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<dd><p>The integer <var>i</var> specifies the value of a numeric attribute. <var>i</var>
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must be non-negative.
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</p>
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<p>The value of a numeric attribute can be specified either with a
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<code>const_int</code>, or as an integer represented as a string in
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<code>const_string</code>, <code>eq_attr</code> (see below), <code>attr</code>,
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<code>symbol_ref</code>, simple arithmetic expressions, and <code>set_attr</code>
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overrides on specific instructions (see <a href="Tagging-Insns.html#Tagging-Insns">Tagging Insns</a>).
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</p>
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<a name="index-const_005fstring-and-attributes"></a>
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</dd>
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<dt><code>(const_string <var>value</var>)</code></dt>
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<dd><p>The string <var>value</var> specifies a constant attribute value.
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If <var>value</var> is specified as ‘<samp>"*"</samp>’, it means that the default value of
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the attribute is to be used for the insn containing this expression.
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‘<samp>"*"</samp>’ obviously cannot be used in the <var>default</var> expression
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of a <code>define_attr</code>.
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</p>
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<p>If the attribute whose value is being specified is numeric, <var>value</var>
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must be a string containing a non-negative integer (normally
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<code>const_int</code> would be used in this case). Otherwise, it must
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contain one of the valid values for the attribute.
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</p>
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<a name="index-if_005fthen_005felse-and-attributes"></a>
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</dd>
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<dt><code>(if_then_else <var>test</var> <var>true-value</var> <var>false-value</var>)</code></dt>
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<dd><p><var>test</var> specifies an attribute test, whose format is defined below.
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The value of this expression is <var>true-value</var> if <var>test</var> is true,
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otherwise it is <var>false-value</var>.
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</p>
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<a name="index-cond-and-attributes"></a>
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</dd>
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<dt><code>(cond [<var>test1</var> <var>value1</var> …] <var>default</var>)</code></dt>
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<dd><p>The first operand of this expression is a vector containing an even
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number of expressions and consisting of pairs of <var>test</var> and <var>value</var>
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expressions. The value of the <code>cond</code> expression is that of the
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<var>value</var> corresponding to the first true <var>test</var> expression. If
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none of the <var>test</var> expressions are true, the value of the <code>cond</code>
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expression is that of the <var>default</var> expression.
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</p></dd>
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</dl>
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<p><var>test</var> expressions can have one of the following forms:
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</p>
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<dl compact="compact">
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<dd><a name="index-const_005fint-and-attribute-tests"></a>
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</dd>
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<dt><code>(const_int <var>i</var>)</code></dt>
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<dd><p>This test is true if <var>i</var> is nonzero and false otherwise.
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</p>
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<a name="index-not-and-attributes"></a>
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<a name="index-ior-and-attributes"></a>
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<a name="index-and-and-attributes"></a>
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</dd>
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<dt><code>(not <var>test</var>)</code></dt>
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<dt><code>(ior <var>test1</var> <var>test2</var>)</code></dt>
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<dt><code>(and <var>test1</var> <var>test2</var>)</code></dt>
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<dd><p>These tests are true if the indicated logical function is true.
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</p>
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<a name="index-match_005foperand-and-attributes"></a>
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</dd>
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<dt><code>(match_operand:<var>m</var> <var>n</var> <var>pred</var> <var>constraints</var>)</code></dt>
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<dd><p>This test is true if operand <var>n</var> of the insn whose attribute value
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is being determined has mode <var>m</var> (this part of the test is ignored
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if <var>m</var> is <code>VOIDmode</code>) and the function specified by the string
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<var>pred</var> returns a nonzero value when passed operand <var>n</var> and mode
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<var>m</var> (this part of the test is ignored if <var>pred</var> is the null
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string).
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</p>
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<p>The <var>constraints</var> operand is ignored and should be the null string.
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</p>
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<a name="index-match_005ftest-and-attributes"></a>
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</dd>
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<dt><code>(match_test <var>c-expr</var>)</code></dt>
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<dd><p>The test is true if C expression <var>c-expr</var> is true. In non-constant
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attributes, <var>c-expr</var> has access to the following variables:
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</p>
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<dl compact="compact">
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<dt><var>insn</var></dt>
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<dd><p>The rtl instruction under test.
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</p></dd>
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<dt><var>which_alternative</var></dt>
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<dd><p>The <code>define_insn</code> alternative that <var>insn</var> matches.
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See <a href="Output-Statement.html#Output-Statement">Output Statement</a>.
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</p></dd>
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<dt><var>operands</var></dt>
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<dd><p>An array of <var>insn</var>’s rtl operands.
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</p></dd>
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</dl>
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<p><var>c-expr</var> behaves like the condition in a C <code>if</code> statement,
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so there is no need to explicitly convert the expression into a boolean
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0 or 1 value. For example, the following two tests are equivalent:
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</p>
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<div class="smallexample">
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<pre class="smallexample">(match_test "x & 2")
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(match_test "(x & 2) != 0")
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</pre></div>
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<a name="index-le-and-attributes"></a>
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<a name="index-leu-and-attributes"></a>
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<a name="index-lt-and-attributes"></a>
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<a name="index-gt-and-attributes"></a>
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<a name="index-gtu-and-attributes"></a>
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<a name="index-ge-and-attributes"></a>
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<a name="index-geu-and-attributes"></a>
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<a name="index-ne-and-attributes"></a>
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<a name="index-eq-and-attributes"></a>
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<a name="index-plus-and-attributes"></a>
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<a name="index-minus-and-attributes"></a>
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<a name="index-mult-and-attributes"></a>
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<a name="index-div-and-attributes"></a>
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<a name="index-mod-and-attributes"></a>
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<a name="index-abs-and-attributes"></a>
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<a name="index-neg-and-attributes"></a>
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<a name="index-ashift-and-attributes"></a>
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<a name="index-lshiftrt-and-attributes"></a>
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<a name="index-ashiftrt-and-attributes"></a>
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</dd>
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<dt><code>(le <var>arith1</var> <var>arith2</var>)</code></dt>
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<dt><code>(leu <var>arith1</var> <var>arith2</var>)</code></dt>
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<dt><code>(lt <var>arith1</var> <var>arith2</var>)</code></dt>
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<dt><code>(ltu <var>arith1</var> <var>arith2</var>)</code></dt>
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<dt><code>(gt <var>arith1</var> <var>arith2</var>)</code></dt>
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<dt><code>(gtu <var>arith1</var> <var>arith2</var>)</code></dt>
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<dt><code>(ge <var>arith1</var> <var>arith2</var>)</code></dt>
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<dt><code>(geu <var>arith1</var> <var>arith2</var>)</code></dt>
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<dt><code>(ne <var>arith1</var> <var>arith2</var>)</code></dt>
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<dt><code>(eq <var>arith1</var> <var>arith2</var>)</code></dt>
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<dd><p>These tests are true if the indicated comparison of the two arithmetic
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expressions is true. Arithmetic expressions are formed with
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<code>plus</code>, <code>minus</code>, <code>mult</code>, <code>div</code>, <code>mod</code>,
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<code>abs</code>, <code>neg</code>, <code>and</code>, <code>ior</code>, <code>xor</code>, <code>not</code>,
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<code>ashift</code>, <code>lshiftrt</code>, and <code>ashiftrt</code> expressions.
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</p>
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<a name="index-get_005fattr"></a>
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<p><code>const_int</code> and <code>symbol_ref</code> are always valid terms (see <a href="Insn-Lengths.html#Insn-Lengths">Insn Lengths</a>,for additional forms). <code>symbol_ref</code> is a string
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denoting a C expression that yields an <code>int</code> when evaluated by the
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‘<samp>get_attr_…</samp>’ routine. It should normally be a global
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variable.
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</p>
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<a name="index-eq_005fattr"></a>
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</dd>
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<dt><code>(eq_attr <var>name</var> <var>value</var>)</code></dt>
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<dd><p><var>name</var> is a string specifying the name of an attribute.
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</p>
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<p><var>value</var> is a string that is either a valid value for attribute
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<var>name</var>, a comma-separated list of values, or ‘<samp>!</samp>’ followed by a
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value or list. If <var>value</var> does not begin with a ‘<samp>!</samp>’, this
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test is true if the value of the <var>name</var> attribute of the current
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insn is in the list specified by <var>value</var>. If <var>value</var> begins
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with a ‘<samp>!</samp>’, this test is true if the attribute’s value is
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<em>not</em> in the specified list.
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</p>
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<p>For example,
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</p>
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<div class="smallexample">
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<pre class="smallexample">(eq_attr "type" "load,store")
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</pre></div>
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<p>is equivalent to
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</p>
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<div class="smallexample">
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<pre class="smallexample">(ior (eq_attr "type" "load") (eq_attr "type" "store"))
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</pre></div>
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<p>If <var>name</var> specifies an attribute of ‘<samp>alternative</samp>’, it refers to the
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value of the compiler variable <code>which_alternative</code>
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(see <a href="Output-Statement.html#Output-Statement">Output Statement</a>) and the values must be small integers. For
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example,
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</p>
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<div class="smallexample">
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<pre class="smallexample">(eq_attr "alternative" "2,3")
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</pre></div>
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<p>is equivalent to
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</p>
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<div class="smallexample">
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<pre class="smallexample">(ior (eq (symbol_ref "which_alternative") (const_int 2))
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(eq (symbol_ref "which_alternative") (const_int 3)))
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</pre></div>
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<p>Note that, for most attributes, an <code>eq_attr</code> test is simplified in cases
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where the value of the attribute being tested is known for all insns matching
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a particular pattern. This is by far the most common case.
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</p>
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<a name="index-attr_005fflag"></a>
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</dd>
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<dt><code>(attr_flag <var>name</var>)</code></dt>
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<dd><p>The value of an <code>attr_flag</code> expression is true if the flag
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specified by <var>name</var> is true for the <code>insn</code> currently being
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scheduled.
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</p>
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<p><var>name</var> is a string specifying one of a fixed set of flags to test.
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Test the flags <code>forward</code> and <code>backward</code> to determine the
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direction of a conditional branch.
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</p>
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<p>This example describes a conditional branch delay slot which
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can be nullified for forward branches that are taken (annul-true) or
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for backward branches which are not taken (annul-false).
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</p>
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<div class="smallexample">
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<pre class="smallexample">(define_delay (eq_attr "type" "cbranch")
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[(eq_attr "in_branch_delay" "true")
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(and (eq_attr "in_branch_delay" "true")
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(attr_flag "forward"))
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(and (eq_attr "in_branch_delay" "true")
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(attr_flag "backward"))])
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</pre></div>
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<p>The <code>forward</code> and <code>backward</code> flags are false if the current
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<code>insn</code> being scheduled is not a conditional branch.
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|
</p>
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||
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<p><code>attr_flag</code> is only used during delay slot scheduling and has no
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meaning to other passes of the compiler.
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||
|
|
</p>
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||
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|
<a name="index-attr"></a>
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</dd>
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||
|
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<dt><code>(attr <var>name</var>)</code></dt>
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|
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<dd><p>The value of another attribute is returned. This is most useful
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for numeric attributes, as <code>eq_attr</code> and <code>attr_flag</code>
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|
produce more efficient code for non-numeric attributes.
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</p></dd>
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</dl>
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<hr>
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<div class="header">
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|
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<p>
|
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|
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Next: <a href="Tagging-Insns.html#Tagging-Insns" accesskey="n" rel="next">Tagging Insns</a>, Previous: <a href="Defining-Attributes.html#Defining-Attributes" accesskey="p" rel="prev">Defining Attributes</a>, Up: <a href="Insn-Attributes.html#Insn-Attributes" accesskey="u" rel="up">Insn Attributes</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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