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121 lines
6.3 KiB
HTML
121 lines
6.3 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>Constraints (GNU Compiler Collection (GCC) Internals)</title>
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<meta name="description" content="Constraints (GNU Compiler Collection (GCC) Internals)">
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<meta name="keywords" content="Constraints (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="Machine-Desc.html#Machine-Desc" rel="up" title="Machine Desc">
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<link href="Simple-Constraints.html#Simple-Constraints" rel="next" title="Simple Constraints">
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<link href="Defining-Predicates.html#Defining-Predicates" rel="prev" title="Defining Predicates">
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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="Constraints"></a>
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<div class="header">
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<p>
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Next: <a href="Standard-Names.html#Standard-Names" accesskey="n" rel="next">Standard Names</a>, Previous: <a href="Predicates.html#Predicates" accesskey="p" rel="prev">Predicates</a>, Up: <a href="Machine-Desc.html#Machine-Desc" accesskey="u" rel="up">Machine Desc</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="Operand-Constraints"></a>
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<h3 class="section">17.8 Operand Constraints</h3>
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<a name="index-operand-constraints"></a>
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<a name="index-constraints"></a>
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<p>Each <code>match_operand</code> in an instruction pattern can specify
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constraints for the operands allowed. The constraints allow you to
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fine-tune matching within the set of operands allowed by the
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predicate.
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</p>
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<p>Constraints can say whether
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an operand may be in a register, and which kinds of register; whether the
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operand can be a memory reference, and which kinds of address; whether the
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operand may be an immediate constant, and which possible values it may
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have. Constraints can also require two operands to match.
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Side-effects aren’t allowed in operands of inline <code>asm</code>, unless
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‘<samp><</samp>’ or ‘<samp>></samp>’ constraints are used, because there is no guarantee
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that the side effects will happen exactly once in an instruction that can update
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the addressing register.
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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="Simple-Constraints.html#Simple-Constraints" accesskey="1">Simple Constraints</a>:</td><td> </td><td align="left" valign="top">Basic use of constraints.
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</td></tr>
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<tr><td align="left" valign="top">• <a href="Multi_002dAlternative.html#Multi_002dAlternative" accesskey="2">Multi-Alternative</a>:</td><td> </td><td align="left" valign="top">When an insn has two alternative constraint-patterns.
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</td></tr>
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<tr><td align="left" valign="top">• <a href="Class-Preferences.html#Class-Preferences" accesskey="3">Class Preferences</a>:</td><td> </td><td align="left" valign="top">Constraints guide which hard register to put things in.
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</td></tr>
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<tr><td align="left" valign="top">• <a href="Modifiers.html#Modifiers" accesskey="4">Modifiers</a>:</td><td> </td><td align="left" valign="top">More precise control over effects of constraints.
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</td></tr>
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<tr><td align="left" valign="top">• <a href="Machine-Constraints.html#Machine-Constraints" accesskey="5">Machine Constraints</a>:</td><td> </td><td align="left" valign="top">Existing constraints for some particular machines.
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</td></tr>
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<tr><td align="left" valign="top">• <a href="Disable-Insn-Alternatives.html#Disable-Insn-Alternatives" accesskey="6">Disable Insn Alternatives</a>:</td><td> </td><td align="left" valign="top">Disable insn alternatives using attributes.
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</td></tr>
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<tr><td align="left" valign="top">• <a href="Define-Constraints.html#Define-Constraints" accesskey="7">Define Constraints</a>:</td><td> </td><td align="left" valign="top">How to define machine-specific constraints.
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</td></tr>
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<tr><td align="left" valign="top">• <a href="C-Constraint-Interface.html#C-Constraint-Interface" accesskey="8">C Constraint Interface</a>:</td><td> </td><td align="left" valign="top">How to test constraints from C code.
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</td></tr>
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</table>
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</body>
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</html>
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