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diff --git a/share/doc/gccint/Predicates.html b/share/doc/gccint/Predicates.html new file mode 100644 index 0000000..ed49177 --- /dev/null +++ b/share/doc/gccint/Predicates.html @@ -0,0 +1,153 @@ +<!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: Predicates</title> + +<meta name="description" content="GNU Compiler Collection (GCC) Internals: Predicates"> +<meta name="keywords" content="GNU Compiler Collection (GCC) Internals: Predicates"> +<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="Machine-Desc.html#Machine-Desc" rel="up" title="Machine Desc"> +<link href="Machine_002dIndependent-Predicates.html#Machine_002dIndependent-Predicates" rel="next" title="Machine-Independent Predicates"> +<link href="Output-Statement.html#Output-Statement" rel="previous" title="Output Statement"> +<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="Predicates"></a> +<div class="header"> +<p> +Next: <a href="Constraints.html#Constraints" accesskey="n" rel="next">Constraints</a>, Previous: <a href="Output-Statement.html#Output-Statement" accesskey="p" rel="previous">Output Statement</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> +</div> +<hr> +<a name="Predicates-1"></a> +<h3 class="section">17.7 Predicates</h3> +<a name="index-predicates"></a> +<a name="index-operand-predicates"></a> +<a name="index-operator-predicates"></a> + +<p>A predicate determines whether a <code>match_operand</code> or +<code>match_operator</code> expression matches, and therefore whether the +surrounding instruction pattern will be used for that combination of +operands. GCC has a number of machine-independent predicates, and you +can define machine-specific predicates as needed. By convention, +predicates used with <code>match_operand</code> have names that end in +‘<samp>_operand</samp>’, and those used with <code>match_operator</code> have names +that end in ‘<samp>_operator</samp>’. +</p> +<p>All predicates are boolean functions (in the mathematical sense) of +two arguments: the RTL expression that is being considered at that +position in the instruction pattern, and the machine mode that the +<code>match_operand</code> or <code>match_operator</code> specifies. In this +section, the first argument is called <var>op</var> and the second argument +<var>mode</var>. Predicates can be called from C as ordinary two-argument +functions; this can be useful in output templates or other +machine-specific code. +</p> +<p>Operand predicates can allow operands that are not actually acceptable +to the hardware, as long as the constraints give reload the ability to +fix them up (see <a href="Constraints.html#Constraints">Constraints</a>). However, GCC will usually generate +better code if the predicates specify the requirements of the machine +instructions as closely as possible. Reload cannot fix up operands +that must be constants (“immediate operands”); you must use a +predicate that allows only constants, or else enforce the requirement +in the extra condition. +</p> +<a name="index-predicates-and-machine-modes"></a> +<a name="index-normal-predicates"></a> +<a name="index-special-predicates"></a> +<p>Most predicates handle their <var>mode</var> argument in a uniform manner. +If <var>mode</var> is <code>VOIDmode</code> (unspecified), then <var>op</var> can have +any mode. If <var>mode</var> is anything else, then <var>op</var> must have the +same mode, unless <var>op</var> is a <code>CONST_INT</code> or integer +<code>CONST_DOUBLE</code>. These RTL expressions always have +<code>VOIDmode</code>, so it would be counterproductive to check that their +mode matches. Instead, predicates that accept <code>CONST_INT</code> and/or +integer <code>CONST_DOUBLE</code> check that the value stored in the +constant will fit in the requested mode. +</p> +<p>Predicates with this behavior are called <em>normal</em>. +<code>genrecog</code> can optimize the instruction recognizer based on +knowledge of how normal predicates treat modes. It can also diagnose +certain kinds of common errors in the use of normal predicates; for +instance, it is almost always an error to use a normal predicate +without specifying a mode. +</p> +<p>Predicates that do something different with their <var>mode</var> argument +are called <em>special</em>. The generic predicates +<code>address_operand</code> and <code>pmode_register_operand</code> are special +predicates. <code>genrecog</code> does not do any optimizations or +diagnosis when special predicates are used. +</p> +<table class="menu" border="0" cellspacing="0"> +<tr><td align="left" valign="top">• <a href="Machine_002dIndependent-Predicates.html#Machine_002dIndependent-Predicates" accesskey="1">Machine-Independent Predicates</a>:</td><td> </td><td align="left" valign="top">Predicates available to all back ends. +</td></tr> +<tr><td align="left" valign="top">• <a href="Defining-Predicates.html#Defining-Predicates" accesskey="2">Defining Predicates</a>:</td><td> </td><td align="left" valign="top">How to write machine-specific predicate + functions. +</td></tr> +</table> + +<hr> +<div class="header"> +<p> +Next: <a href="Constraints.html#Constraints" accesskey="n" rel="next">Constraints</a>, Previous: <a href="Output-Statement.html#Output-Statement" accesskey="p" rel="previous">Output Statement</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> +</div> + + + +</body> +</html> |