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120 lines
5.3 KiB
HTML
120 lines
5.3 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>Assembler (GNU Compiler Collection (GCC) Internals)</title>
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<meta name="description" content="Assembler (GNU Compiler Collection (GCC) Internals)">
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<meta name="keywords" content="Assembler (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="RTL.html#RTL" rel="up" title="RTL">
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<link href="Debug-Information.html#Debug-Information" rel="next" title="Debug Information">
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<link href="Incdec.html#Incdec" rel="prev" title="Incdec">
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<style type="text/css">
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<!--
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a.summary-letter {text-decoration: none}
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blockquote.indentedblock {margin-right: 0em}
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blockquote.smallindentedblock {margin-right: 0em; font-size: smaller}
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blockquote.smallquotation {font-size: smaller}
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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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div.smallexample {margin-left: 3.2em}
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div.smalllisp {margin-left: 3.2em}
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kbd {font-style: oblique}
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pre.display {font-family: inherit}
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pre.format {font-family: inherit}
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pre.menu-comment {font-family: serif}
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pre.menu-preformatted {font-family: serif}
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pre.smalldisplay {font-family: inherit; font-size: smaller}
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pre.smallexample {font-size: smaller}
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pre.smallformat {font-family: inherit; font-size: smaller}
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pre.smalllisp {font-size: smaller}
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span.nolinebreak {white-space: nowrap}
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span.roman {font-family: initial; font-weight: normal}
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span.sansserif {font-family: sans-serif; font-weight: normal}
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ul.no-bullet {list-style: none}
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-->
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</style>
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</head>
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<body lang="en">
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<a name="Assembler"></a>
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<div class="header">
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<p>
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Next: <a href="Debug-Information.html#Debug-Information" accesskey="n" rel="next">Debug Information</a>, Previous: <a href="Incdec.html#Incdec" accesskey="p" rel="prev">Incdec</a>, Up: <a href="RTL.html#RTL" accesskey="u" rel="up">RTL</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="Assembler-Instructions-as-Expressions"></a>
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<h3 class="section">14.17 Assembler Instructions as Expressions</h3>
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<a name="index-assembler-instructions-in-RTL"></a>
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<a name="index-asm_005foperands_002c-usage"></a>
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<p>The RTX code <code>asm_operands</code> represents a value produced by a
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user-specified assembler instruction. It is used to represent
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an <code>asm</code> statement with arguments. An <code>asm</code> statement with
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a single output operand, like this:
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</p>
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<div class="smallexample">
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<pre class="smallexample">asm ("foo %1,%2,%0" : "=a" (outputvar) : "g" (x + y), "di" (*z));
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</pre></div>
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<p>is represented using a single <code>asm_operands</code> RTX which represents
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the value that is stored in <code>outputvar</code>:
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</p>
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<div class="smallexample">
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<pre class="smallexample">(set <var>rtx-for-outputvar</var>
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(asm_operands "foo %1,%2,%0" "a" 0
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[<var>rtx-for-addition-result</var> <var>rtx-for-*z</var>]
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[(asm_input:<var>m1</var> "g")
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(asm_input:<var>m2</var> "di")]))
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</pre></div>
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<p>Here the operands of the <code>asm_operands</code> RTX are the assembler
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template string, the output-operand’s constraint, the index-number of the
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output operand among the output operands specified, a vector of input
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operand RTX’s, and a vector of input-operand modes and constraints. The
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mode <var>m1</var> is the mode of the sum <code>x+y</code>; <var>m2</var> is that of
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<code>*z</code>.
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</p>
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<p>When an <code>asm</code> statement has multiple output values, its insn has
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several such <code>set</code> RTX’s inside of a <code>parallel</code>. Each <code>set</code>
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contains an <code>asm_operands</code>; all of these share the same assembler
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template and vectors, but each contains the constraint for the respective
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output operand. They are also distinguished by the output-operand index
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number, which is 0, 1, … for successive output operands.
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</p>
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</body>
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</html>
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