aarch64-linux-gnu-4.9/share/doc/gccint/RTL-Classes.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: RTL Classes</title>

 <meta name="description" content="GNU Compiler Collection (GCC) Internals: RTL Classes">
 <meta name="keywords" content="GNU Compiler Collection (GCC) Internals: RTL Classes">
 <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="RTL.html#RTL" rel="up" title="RTL">
 <link href="Accessors.html#Accessors" rel="next" title="Accessors">
 <link href="RTL-Objects.html#RTL-Objects" rel="prev" title="RTL Objects">
 <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="RTL-Classes"></a>
 <div class="header">
 <p>
 Next: <a href="Accessors.html#Accessors" accesskey="n" rel="next">Accessors</a>, Previous: <a href="RTL-Objects.html#RTL-Objects" accesskey="p" rel="prev">RTL Objects</a>, Up: <a href="RTL.html#RTL" accesskey="u" rel="up">RTL</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-Classes-and-Formats"></a>
 <h3 class="section">13.2 RTL Classes and Formats</h3>
 <a name="index-RTL-classes"></a>
 <a name="index-classes-of-RTX-codes"></a>
 <a name="index-RTX-codes_002c-classes-of"></a>
 <a name="index-GET_005fRTX_005fCLASS"></a>

 <p>The various expression codes are divided into several <em>classes</em>,
 which are represented by single characters.  You can determine the class
 of an RTX code with the macro <code>GET_RTX_CLASS (<var>code</var>)</code>.
 Currently, <samp>rtl.def</samp> defines these classes:
 </p>
 <dl compact="compact">
 <dt><code>RTX_OBJ</code></dt>
 <dd><p>An RTX code that represents an actual object, such as a register
 (<code>REG</code>) or a memory location (<code>MEM</code>, <code>SYMBOL_REF</code>).
 <code>LO_SUM</code>) is also included; instead, <code>SUBREG</code> and
 <code>STRICT_LOW_PART</code> are not in this class, but in class <code>x</code>.
 </p>
 </dd>
 <dt><code>RTX_CONST_OBJ</code></dt>
 <dd><p>An RTX code that represents a constant object.  <code>HIGH</code> is also
 included in this class.
 </p>
 </dd>
 <dt><code>RTX_COMPARE</code></dt>
 <dd><p>An RTX code for a non-symmetric comparison, such as <code>GEU</code> or
 <code>LT</code>.
 </p>
 </dd>
 <dt><code>RTX_COMM_COMPARE</code></dt>
 <dd><p>An RTX code for a symmetric (commutative) comparison, such as <code>EQ</code>
 or <code>ORDERED</code>.
 </p>
 </dd>
 <dt><code>RTX_UNARY</code></dt>
 <dd><p>An RTX code for a unary arithmetic operation, such as <code>NEG</code>,
 <code>NOT</code>, or <code>ABS</code>.  This category also includes value extension
 (sign or zero) and conversions between integer and floating point.
 </p>
 </dd>
 <dt><code>RTX_COMM_ARITH</code></dt>
 <dd><p>An RTX code for a commutative binary operation, such as <code>PLUS</code> or
 <code>AND</code>.  <code>NE</code> and <code>EQ</code> are comparisons, so they have class
 <code>&lt;</code>.
 </p>
 </dd>
 <dt><code>RTX_BIN_ARITH</code></dt>
 <dd><p>An RTX code for a non-commutative binary operation, such as <code>MINUS</code>,
 <code>DIV</code>, or <code>ASHIFTRT</code>.
 </p>
 </dd>
 <dt><code>RTX_BITFIELD_OPS</code></dt>
 <dd><p>An RTX code for a bit-field operation.  Currently only
 <code>ZERO_EXTRACT</code> and <code>SIGN_EXTRACT</code>.  These have three inputs
 and are lvalues (so they can be used for insertion as well).
 See <a href="Bit_002dFields.html#Bit_002dFields">Bit-Fields</a>.
 </p>
 </dd>
 <dt><code>RTX_TERNARY</code></dt>
 <dd><p>An RTX code for other three input operations.  Currently only
 <code>IF_THEN_ELSE</code>,  <code>VEC_MERGE</code>, <code>SIGN_EXTRACT</code>,
 <code>ZERO_EXTRACT</code>, and <code>FMA</code>.
 </p>
 </dd>
 <dt><code>RTX_INSN</code></dt>
 <dd><p>An RTX code for an entire instruction:  <code>INSN</code>, <code>JUMP_INSN</code>, and
 <code>CALL_INSN</code>.  See <a href="Insns.html#Insns">Insns</a>.
 </p>
 </dd>
 <dt><code>RTX_MATCH</code></dt>
 <dd><p>An RTX code for something that matches in insns, such as
 <code>MATCH_DUP</code>.  These only occur in machine descriptions.
 </p>
 </dd>
 <dt><code>RTX_AUTOINC</code></dt>
 <dd><p>An RTX code for an auto-increment addressing mode, such as
 <code>POST_INC</code>.
 </p>
 </dd>
 <dt><code>RTX_EXTRA</code></dt>
 <dd><p>All other RTX codes.  This category includes the remaining codes used
 only in machine descriptions (<code>DEFINE_*</code>, etc.).  It also includes
 all the codes describing side effects (<code>SET</code>, <code>USE</code>,
 <code>CLOBBER</code>, etc.) and the non-insns that may appear on an insn
 chain, such as <code>NOTE</code>, <code>BARRIER</code>, and <code>CODE_LABEL</code>.
 <code>SUBREG</code> is also part of this class.
 </p></dd>
 </dl>

 <a name="index-RTL-format"></a>
 <p>For each expression code, <samp>rtl.def</samp> specifies the number of
 contained objects and their kinds using a sequence of characters
 called the <em>format</em> of the expression code.  For example,
 the format of <code>subreg</code> is &lsquo;<samp>ei</samp>&rsquo;.
 </p>
 <a name="index-RTL-format-characters"></a>
 <p>These are the most commonly used format characters:
 </p>
 <dl compact="compact">
 <dt><code>e</code></dt>
 <dd><p>An expression (actually a pointer to an expression).
 </p>
 </dd>
 <dt><code>i</code></dt>
 <dd><p>An integer.
 </p>
 </dd>
 <dt><code>w</code></dt>
 <dd><p>A wide integer.
 </p>
 </dd>
 <dt><code>s</code></dt>
 <dd><p>A string.
 </p>
 </dd>
 <dt><code>E</code></dt>
 <dd><p>A vector of expressions.
 </p></dd>
 </dl>

 <p>A few other format characters are used occasionally:
 </p>
 <dl compact="compact">
 <dt><code>u</code></dt>
 <dd><p>&lsquo;<samp>u</samp>&rsquo; is equivalent to &lsquo;<samp>e</samp>&rsquo; except that it is printed differently
 in debugging dumps.  It is used for pointers to insns.
 </p>
 </dd>
 <dt><code>n</code></dt>
 <dd><p>&lsquo;<samp>n</samp>&rsquo; is equivalent to &lsquo;<samp>i</samp>&rsquo; except that it is printed differently
 in debugging dumps.  It is used for the line number or code number of a
 <code>note</code> insn.
 </p>
 </dd>
 <dt><code>S</code></dt>
 <dd><p>&lsquo;<samp>S</samp>&rsquo; indicates a string which is optional.  In the RTL objects in
 core, &lsquo;<samp>S</samp>&rsquo; is equivalent to &lsquo;<samp>s</samp>&rsquo;, but when the object is read,
 from an &lsquo;<samp>md</samp>&rsquo; file, the string value of this operand may be omitted.
 An omitted string is taken to be the null string.
 </p>
 </dd>
 <dt><code>V</code></dt>
 <dd><p>&lsquo;<samp>V</samp>&rsquo; indicates a vector which is optional.  In the RTL objects in
 core, &lsquo;<samp>V</samp>&rsquo; is equivalent to &lsquo;<samp>E</samp>&rsquo;, but when the object is read
 from an &lsquo;<samp>md</samp>&rsquo; file, the vector value of this operand may be omitted.
 An omitted vector is effectively the same as a vector of no elements.
 </p>
 </dd>
 <dt><code>B</code></dt>
 <dd><p>&lsquo;<samp>B</samp>&rsquo; indicates a pointer to basic block structure.
 </p>
 </dd>
 <dt><code>0</code></dt>
 <dd><p>&lsquo;<samp>0</samp>&rsquo; means a slot whose contents do not fit any normal category.
 &lsquo;<samp>0</samp>&rsquo; slots are not printed at all in dumps, and are often used in
 special ways by small parts of the compiler.
 </p></dd>
 </dl>

 <p>There are macros to get the number of operands and the format
 of an expression code:
 </p>
 <dl compact="compact">
 <dd><a name="index-GET_005fRTX_005fLENGTH"></a>
 </dd>
 <dt><code>GET_RTX_LENGTH (<var>code</var>)</code></dt>
 <dd><p>Number of operands of an RTX of code <var>code</var>.
 </p>
 <a name="index-GET_005fRTX_005fFORMAT"></a>
 </dd>
 <dt><code>GET_RTX_FORMAT (<var>code</var>)</code></dt>
 <dd><p>The format of an RTX of code <var>code</var>, as a C string.
 </p></dd>
 </dl>

 <p>Some classes of RTX codes always have the same format.  For example, it
 is safe to assume that all comparison operations have format <code>ee</code>.
 </p>
 <dl compact="compact">
 <dt><code>1</code></dt>
 <dd><p>All codes of this class have format <code>e</code>.
 </p>
 </dd>
 <dt><code>&lt;</code></dt>
 <dt><code>c</code></dt>
 <dt><code>2</code></dt>
 <dd><p>All codes of these classes have format <code>ee</code>.
 </p>
 </dd>
 <dt><code>b</code></dt>
 <dt><code>3</code></dt>
 <dd><p>All codes of these classes have format <code>eee</code>.
 </p>
 </dd>
 <dt><code>i</code></dt>
 <dd><p>All codes of this class have formats that begin with <code>iuueiee</code>.
 See <a href="Insns.html#Insns">Insns</a>.  Note that not all RTL objects linked onto an insn chain
 are of class <code>i</code>.
 </p>
 </dd>
 <dt><code>o</code></dt>
 <dt><code>m</code></dt>
 <dt><code>x</code></dt>
 <dd><p>You can make no assumptions about the format of these codes.
 </p></dd>
 </dl>

 <hr>
 <div class="header">
 <p>
 Next: <a href="Accessors.html#Accessors" accesskey="n" rel="next">Accessors</a>, Previous: <a href="RTL-Objects.html#RTL-Objects" accesskey="p" rel="prev">RTL Objects</a>, Up: <a href="RTL.html#RTL" accesskey="u" rel="up">RTL</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: RTL Classes</title>

	<meta name="description" content="GNU Compiler Collection (GCC) Internals: RTL Classes">
	<meta name="keywords" content="GNU Compiler Collection (GCC) Internals: RTL Classes">
	<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="RTL.html#RTL" rel="up" title="RTL">
	<link href="Accessors.html#Accessors" rel="next" title="Accessors">
	<link href="RTL-Objects.html#RTL-Objects" rel="prev" title="RTL Objects">
	<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="RTL-Classes"></a>
	<div class="header">
	<p>
	Next: <a href="Accessors.html#Accessors" accesskey="n" rel="next">Accessors</a>, Previous: <a href="RTL-Objects.html#RTL-Objects" accesskey="p" rel="prev">RTL Objects</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>
	</div>
	<hr>
	<a name="RTL-Classes-and-Formats"></a>
	<h3 class="section">13.2 RTL Classes and Formats</h3>
	<a name="index-RTL-classes"></a>
	<a name="index-classes-of-RTX-codes"></a>
	<a name="index-RTX-codes_002c-classes-of"></a>
	<a name="index-GET_005fRTX_005fCLASS"></a>

	<p>The various expression codes are divided into several <em>classes</em>,
	which are represented by single characters. You can determine the class
	of an RTX code with the macro <code>GET_RTX_CLASS (<var>code</var>)</code>.
	Currently, <samp>rtl.def</samp> defines these classes:
	</p>
	<dl compact="compact">
	<dt><code>RTX_OBJ</code></dt>
	<dd><p>An RTX code that represents an actual object, such as a register
	(<code>REG</code>) or a memory location (<code>MEM</code>, <code>SYMBOL_REF</code>).
	<code>LO_SUM</code>) is also included; instead, <code>SUBREG</code> and
	<code>STRICT_LOW_PART</code> are not in this class, but in class <code>x</code>.
	</p>
	</dd>
	<dt><code>RTX_CONST_OBJ</code></dt>
	<dd><p>An RTX code that represents a constant object. <code>HIGH</code> is also
	included in this class.
	</p>
	</dd>
	<dt><code>RTX_COMPARE</code></dt>
	<dd><p>An RTX code for a non-symmetric comparison, such as <code>GEU</code> or
	<code>LT</code>.
	</p>
	</dd>
	<dt><code>RTX_COMM_COMPARE</code></dt>
	<dd><p>An RTX code for a symmetric (commutative) comparison, such as <code>EQ</code>
	or <code>ORDERED</code>.
	</p>
	</dd>
	<dt><code>RTX_UNARY</code></dt>
	<dd><p>An RTX code for a unary arithmetic operation, such as <code>NEG</code>,
	<code>NOT</code>, or <code>ABS</code>. This category also includes value extension
	(sign or zero) and conversions between integer and floating point.
	</p>
	</dd>
	<dt><code>RTX_COMM_ARITH</code></dt>
	<dd><p>An RTX code for a commutative binary operation, such as <code>PLUS</code> or
	<code>AND</code>. <code>NE</code> and <code>EQ</code> are comparisons, so they have class
	<code><</code>.
	</p>
	</dd>
	<dt><code>RTX_BIN_ARITH</code></dt>
	<dd><p>An RTX code for a non-commutative binary operation, such as <code>MINUS</code>,
	<code>DIV</code>, or <code>ASHIFTRT</code>.
	</p>
	</dd>
	<dt><code>RTX_BITFIELD_OPS</code></dt>
	<dd><p>An RTX code for a bit-field operation. Currently only
	<code>ZERO_EXTRACT</code> and <code>SIGN_EXTRACT</code>. These have three inputs
	and are lvalues (so they can be used for insertion as well).
	See <a href="Bit_002dFields.html#Bit_002dFields">Bit-Fields</a>.
	</p>
	</dd>
	<dt><code>RTX_TERNARY</code></dt>
	<dd><p>An RTX code for other three input operations. Currently only
	<code>IF_THEN_ELSE</code>, <code>VEC_MERGE</code>, <code>SIGN_EXTRACT</code>,
	<code>ZERO_EXTRACT</code>, and <code>FMA</code>.
	</p>
	</dd>
	<dt><code>RTX_INSN</code></dt>
	<dd><p>An RTX code for an entire instruction: <code>INSN</code>, <code>JUMP_INSN</code>, and
	<code>CALL_INSN</code>. See <a href="Insns.html#Insns">Insns</a>.
	</p>
	</dd>
	<dt><code>RTX_MATCH</code></dt>
	<dd><p>An RTX code for something that matches in insns, such as
	<code>MATCH_DUP</code>. These only occur in machine descriptions.
	</p>
	</dd>
	<dt><code>RTX_AUTOINC</code></dt>
	<dd><p>An RTX code for an auto-increment addressing mode, such as
	<code>POST_INC</code>.
	</p>
	</dd>
	<dt><code>RTX_EXTRA</code></dt>
	<dd><p>All other RTX codes. This category includes the remaining codes used
	only in machine descriptions (<code>DEFINE_*</code>, etc.). It also includes
	all the codes describing side effects (<code>SET</code>, <code>USE</code>,
	<code>CLOBBER</code>, etc.) and the non-insns that may appear on an insn
	chain, such as <code>NOTE</code>, <code>BARRIER</code>, and <code>CODE_LABEL</code>.
	<code>SUBREG</code> is also part of this class.
	</p></dd>
	</dl>

	<a name="index-RTL-format"></a>
	<p>For each expression code, <samp>rtl.def</samp> specifies the number of
	contained objects and their kinds using a sequence of characters
	called the <em>format</em> of the expression code. For example,
	the format of <code>subreg</code> is ‘<samp>ei</samp>’.
	</p>
	<a name="index-RTL-format-characters"></a>
	<p>These are the most commonly used format characters:
	</p>
	<dl compact="compact">
	<dt><code>e</code></dt>
	<dd><p>An expression (actually a pointer to an expression).
	</p>
	</dd>
	<dt><code>i</code></dt>
	<dd><p>An integer.
	</p>
	</dd>
	<dt><code>w</code></dt>
	<dd><p>A wide integer.
	</p>
	</dd>
	<dt><code>s</code></dt>
	<dd><p>A string.
	</p>
	</dd>
	<dt><code>E</code></dt>
	<dd><p>A vector of expressions.
	</p></dd>
	</dl>

	<p>A few other format characters are used occasionally:
	</p>
	<dl compact="compact">
	<dt><code>u</code></dt>
	<dd><p>‘<samp>u</samp>’ is equivalent to ‘<samp>e</samp>’ except that it is printed differently
	in debugging dumps. It is used for pointers to insns.
	</p>
	</dd>
	<dt><code>n</code></dt>
	<dd><p>‘<samp>n</samp>’ is equivalent to ‘<samp>i</samp>’ except that it is printed differently
	in debugging dumps. It is used for the line number or code number of a
	<code>note</code> insn.
	</p>
	</dd>
	<dt><code>S</code></dt>
	<dd><p>‘<samp>S</samp>’ indicates a string which is optional. In the RTL objects in
	core, ‘<samp>S</samp>’ is equivalent to ‘<samp>s</samp>’, but when the object is read,
	from an ‘<samp>md</samp>’ file, the string value of this operand may be omitted.
	An omitted string is taken to be the null string.
	</p>
	</dd>
	<dt><code>V</code></dt>
	<dd><p>‘<samp>V</samp>’ indicates a vector which is optional. In the RTL objects in
	core, ‘<samp>V</samp>’ is equivalent to ‘<samp>E</samp>’, but when the object is read
	from an ‘<samp>md</samp>’ file, the vector value of this operand may be omitted.
	An omitted vector is effectively the same as a vector of no elements.
	</p>
	</dd>
	<dt><code>B</code></dt>
	<dd><p>‘<samp>B</samp>’ indicates a pointer to basic block structure.
	</p>
	</dd>
	<dt><code>0</code></dt>
	<dd><p>‘<samp>0</samp>’ means a slot whose contents do not fit any normal category.
	‘<samp>0</samp>’ slots are not printed at all in dumps, and are often used in
	special ways by small parts of the compiler.
	</p></dd>
	</dl>

	<p>There are macros to get the number of operands and the format
	of an expression code:
	</p>
	<dl compact="compact">
	<dd><a name="index-GET_005fRTX_005fLENGTH"></a>
	</dd>
	<dt><code>GET_RTX_LENGTH (<var>code</var>)</code></dt>
	<dd><p>Number of operands of an RTX of code <var>code</var>.
	</p>
	<a name="index-GET_005fRTX_005fFORMAT"></a>
	</dd>
	<dt><code>GET_RTX_FORMAT (<var>code</var>)</code></dt>
	<dd><p>The format of an RTX of code <var>code</var>, as a C string.
	</p></dd>
	</dl>

	<p>Some classes of RTX codes always have the same format. For example, it
	is safe to assume that all comparison operations have format <code>ee</code>.
	</p>
	<dl compact="compact">
	<dt><code>1</code></dt>
	<dd><p>All codes of this class have format <code>e</code>.
	</p>
	</dd>
	<dt><code><</code></dt>
	<dt><code>c</code></dt>
	<dt><code>2</code></dt>
	<dd><p>All codes of these classes have format <code>ee</code>.
	</p>
	</dd>
	<dt><code>b</code></dt>
	<dt><code>3</code></dt>
	<dd><p>All codes of these classes have format <code>eee</code>.
	</p>
	</dd>
	<dt><code>i</code></dt>
	<dd><p>All codes of this class have formats that begin with <code>iuueiee</code>.
	See <a href="Insns.html#Insns">Insns</a>. Note that not all RTL objects linked onto an insn chain
	are of class <code>i</code>.
	</p>
	</dd>
	<dt><code>o</code></dt>
	<dt><code>m</code></dt>
	<dt><code>x</code></dt>
	<dd><p>You can make no assumptions about the format of these codes.
	</p></dd>
	</dl>

	<hr>
	<div class="header">
	<p>
	Next: <a href="Accessors.html#Accessors" accesskey="n" rel="next">Accessors</a>, Previous: <a href="RTL-Objects.html#RTL-Objects" accesskey="p" rel="prev">RTL Objects</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>
	</div>



	</body>
	</html>