aarch64-linux-gnu-4.9/share/doc/gccint/Define-Subst.html - toolchains/linux-x86/gcc - Git at Google

 <!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
 <html>
 <!-- Copyright (C) 1988-2015 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 5.2, http://www.gnu.org/software/texinfo/ -->
 <head>
 <title>GNU Compiler Collection (GCC) Internals: Define Subst</title>

 <meta name="description" content="GNU Compiler Collection (GCC) Internals: Define Subst">
 <meta name="keywords" content="GNU Compiler Collection (GCC) Internals: Define Subst">
 <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="Define-Subst-Example.html#Define-Subst-Example" rel="next" title="Define Subst Example">
 <link href="Conditional-Execution.html#Conditional-Execution" rel="prev" title="Conditional Execution">
 <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="Define-Subst"></a>
 <div class="header">
 <p>
 Next: <a href="Constant-Definitions.html#Constant-Definitions" accesskey="n" rel="next">Constant Definitions</a>, Previous: <a href="Conditional-Execution.html#Conditional-Execution" accesskey="p" rel="prev">Conditional Execution</a>, Up: <a href="Machine-Desc.html#Machine-Desc" accesskey="u" rel="up">Machine Desc</a> &nbsp; [<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="RTL-Templates-Transformations"></a>
 <h3 class="section">16.21 RTL Templates Transformations</h3>
 <a name="index-define_005fsubst"></a>

 <p>For some hardware architectures there are common cases when the RTL
 templates for the instructions can be derived from the other RTL
 templates using simple transformations.  E.g., <samp>i386.md</samp> contains
 an RTL template for the ordinary <code>sub</code> instruction&mdash;
 <code>*subsi_1</code>, and for the <code>sub</code> instruction with subsequent
 zero-extension&mdash;<code>*subsi_1_zext</code>.  Such cases can be easily
 implemented by a single meta-template capable of generating a modified
 case based on the initial one:
 </p>
 <a name="index-define_005fsubst-4"></a>
 <div class="smallexample">
 <pre class="smallexample">(define_subst &quot;<var>name</var>&quot;
   [<var>input-template</var>]
   &quot;<var>condition</var>&quot;
   [<var>output-template</var>])
 </pre></div>
 <p><var>input-template</var> is a pattern describing the source RTL template,
 which will be transformed.
 </p>
 <p><var>condition</var> is a C expression that is conjunct with the condition
 from the input-template to generate a condition to be used in the
 output-template.
 </p>
 <p><var>output-template</var> is a pattern that will be used in the resulting
 template.
 </p>
 <p><code>define_subst</code> mechanism is tightly coupled with the notion of the
 subst attribute (see <a href="Subst-Iterators.html#Subst-Iterators">Subst Iterators</a>).  The use of
 <code>define_subst</code> is triggered by a reference to a subst attribute in
 the transforming RTL template.  This reference initiates duplication of
 the source RTL template and substitution of the attributes with their
 values.  The source RTL template is left unchanged, while the copy is
 transformed by <code>define_subst</code>.  This transformation can fail in the
 case when the source RTL template is not matched against the
 input-template of the <code>define_subst</code>.  In such case the copy is
 deleted.
 </p>
 <p><code>define_subst</code> can be used only in <code>define_insn</code> and
 <code>define_expand</code>, it cannot be used in other expressions (e.g. in
 <code>define_insn_and_split</code>).
 </p>
 <table class="menu" border="0" cellspacing="0">
 <tr><td align="left" valign="top">&bull; <a href="Define-Subst-Example.html#Define-Subst-Example" accesskey="1">Define Subst Example</a>:</td><td>&nbsp;&nbsp;</td><td align="left" valign="top">Example of <code>define_subst</code> work.
 </td></tr>
 <tr><td align="left" valign="top">&bull; <a href="Define-Subst-Pattern-Matching.html#Define-Subst-Pattern-Matching" accesskey="2">Define Subst Pattern Matching</a>:</td><td>&nbsp;&nbsp;</td><td align="left" valign="top">Process of template comparison.
 </td></tr>
 <tr><td align="left" valign="top">&bull; <a href="Define-Subst-Output-Template.html#Define-Subst-Output-Template" accesskey="3">Define Subst Output Template</a>:</td><td>&nbsp;&nbsp;</td><td align="left" valign="top">Generation of output template.
 </td></tr>
 </table>

 <hr>
 <div class="header">
 <p>
 Next: <a href="Constant-Definitions.html#Constant-Definitions" accesskey="n" rel="next">Constant Definitions</a>, Previous: <a href="Conditional-Execution.html#Conditional-Execution" accesskey="p" rel="prev">Conditional Execution</a>, Up: <a href="Machine-Desc.html#Machine-Desc" accesskey="u" rel="up">Machine Desc</a> &nbsp; [<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>
	<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
	<html>
	<!-- Copyright (C) 1988-2015 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 5.2, http://www.gnu.org/software/texinfo/ -->
	<head>
	<title>GNU Compiler Collection (GCC) Internals: Define Subst</title>

	<meta name="description" content="GNU Compiler Collection (GCC) Internals: Define Subst">
	<meta name="keywords" content="GNU Compiler Collection (GCC) Internals: Define Subst">
	<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="Define-Subst-Example.html#Define-Subst-Example" rel="next" title="Define Subst Example">
	<link href="Conditional-Execution.html#Conditional-Execution" rel="prev" title="Conditional Execution">
	<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="Define-Subst"></a>
	<div class="header">
	<p>
	Next: <a href="Constant-Definitions.html#Constant-Definitions" accesskey="n" rel="next">Constant Definitions</a>, Previous: <a href="Conditional-Execution.html#Conditional-Execution" accesskey="p" rel="prev">Conditional Execution</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="RTL-Templates-Transformations"></a>
	<h3 class="section">16.21 RTL Templates Transformations</h3>
	<a name="index-define_005fsubst"></a>

	<p>For some hardware architectures there are common cases when the RTL
	templates for the instructions can be derived from the other RTL
	templates using simple transformations. E.g., <samp>i386.md</samp> contains
	an RTL template for the ordinary <code>sub</code> instruction—
	<code>*subsi_1</code>, and for the <code>sub</code> instruction with subsequent
	zero-extension—<code>*subsi_1_zext</code>. Such cases can be easily
	implemented by a single meta-template capable of generating a modified
	case based on the initial one:
	</p>
	<a name="index-define_005fsubst-4"></a>
	<div class="smallexample">
	<pre class="smallexample">(define_subst "<var>name</var>"
	[<var>input-template</var>]
	"<var>condition</var>"
	[<var>output-template</var>])
	</pre></div>
	<p><var>input-template</var> is a pattern describing the source RTL template,
	which will be transformed.
	</p>
	<p><var>condition</var> is a C expression that is conjunct with the condition
	from the input-template to generate a condition to be used in the
	output-template.
	</p>
	<p><var>output-template</var> is a pattern that will be used in the resulting
	template.
	</p>
	<p><code>define_subst</code> mechanism is tightly coupled with the notion of the
	subst attribute (see <a href="Subst-Iterators.html#Subst-Iterators">Subst Iterators</a>). The use of
	<code>define_subst</code> is triggered by a reference to a subst attribute in
	the transforming RTL template. This reference initiates duplication of
	the source RTL template and substitution of the attributes with their
	values. The source RTL template is left unchanged, while the copy is
	transformed by <code>define_subst</code>. This transformation can fail in the
	case when the source RTL template is not matched against the
	input-template of the <code>define_subst</code>. In such case the copy is
	deleted.
	</p>
	<p><code>define_subst</code> can be used only in <code>define_insn</code> and
	<code>define_expand</code>, it cannot be used in other expressions (e.g. in
	<code>define_insn_and_split</code>).
	</p>
	<table class="menu" border="0" cellspacing="0">
	<tr><td align="left" valign="top">• <a href="Define-Subst-Example.html#Define-Subst-Example" accesskey="1">Define Subst Example</a>:</td><td>  </td><td align="left" valign="top">Example of <code>define_subst</code> work.
	</td></tr>
	<tr><td align="left" valign="top">• <a href="Define-Subst-Pattern-Matching.html#Define-Subst-Pattern-Matching" accesskey="2">Define Subst Pattern Matching</a>:</td><td>  </td><td align="left" valign="top">Process of template comparison.
	</td></tr>
	<tr><td align="left" valign="top">• <a href="Define-Subst-Output-Template.html#Define-Subst-Output-Template" accesskey="3">Define Subst Output Template</a>:</td><td>  </td><td align="left" valign="top">Generation of output template.
	</td></tr>
	</table>

	<hr>
	<div class="header">
	<p>
	Next: <a href="Constant-Definitions.html#Constant-Definitions" accesskey="n" rel="next">Constant Definitions</a>, Previous: <a href="Conditional-Execution.html#Conditional-Execution" accesskey="p" rel="prev">Conditional Execution</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>