visus
/
toolchain-gcc-arm-embedded


			
							<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
<!-- Copyright (C) 1988-2020 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 6.5, http://www.gnu.org/software/texinfo/ -->
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
<title>Code Iterators (GNU Compiler Collection (GCC) Internals)</title>

<meta name="description" content="Code Iterators (GNU Compiler Collection (GCC) Internals)">
<meta name="keywords" content="Code Iterators (GNU Compiler Collection (GCC) Internals)">
<meta name="resource-type" content="document">
<meta name="distribution" content="global">
<meta name="Generator" content="makeinfo">
<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="Iterators.html#Iterators" rel="up" title="Iterators">
<link href="Int-Iterators.html#Int-Iterators" rel="next" title="Int Iterators">
<link href="Examples.html#Examples" rel="prev" title="Examples">
<style type="text/css">
<!--
a.summary-letter {text-decoration: none}
blockquote.indentedblock {margin-right: 0em}
blockquote.smallindentedblock {margin-right: 0em; font-size: smaller}
blockquote.smallquotation {font-size: smaller}
div.display {margin-left: 3.2em}
div.example {margin-left: 3.2em}
div.lisp {margin-left: 3.2em}
div.smalldisplay {margin-left: 3.2em}
div.smallexample {margin-left: 3.2em}
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.nolinebreak {white-space: nowrap}
span.roman {font-family: initial; font-weight: normal}
span.sansserif {font-family: sans-serif; font-weight: normal}
ul.no-bullet {list-style: none}
-->
</style>


</head>

<body lang="en">
<a name="Code-Iterators"></a>
<div class="header">
<p>
Next: <a href="Int-Iterators.html#Int-Iterators" accesskey="n" rel="next">Int Iterators</a>, Previous: <a href="Mode-Iterators.html#Mode-Iterators" accesskey="p" rel="prev">Mode Iterators</a>, Up: <a href="Iterators.html#Iterators" accesskey="u" rel="up">Iterators</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="Code-Iterators-1"></a>
<h4 class="subsection">17.23.2 Code Iterators</h4>
<a name="index-code-iterators-in-_002emd-files"></a>
<a name="index-define_005fcode_005fiterator"></a>
<a name="index-define_005fcode_005fattr"></a>

<p>Code iterators operate in a similar way to mode iterators.  See <a href="Mode-Iterators.html#Mode-Iterators">Mode Iterators</a>.
</p>
<p>The construct:
</p>
<div class="smallexample">
<pre class="smallexample">(define_code_iterator <var>name</var> [(<var>code1</var> &quot;<var>cond1</var>&quot;) &hellip; (<var>coden</var> &quot;<var>condn</var>&quot;)])
</pre></div>

<p>defines a pseudo rtx code <var>name</var> that can be instantiated as
<var>codei</var> if condition <var>condi</var> is true.  Each <var>codei</var>
must have the same rtx format.  See <a href="RTL-Classes.html#RTL-Classes">RTL Classes</a>.
</p>
<p>As with mode iterators, each pattern that uses <var>name</var> will be
expanded <var>n</var> times, once with all uses of <var>name</var> replaced by
<var>code1</var>, once with all uses replaced by <var>code2</var>, and so on.
See <a href="Defining-Mode-Iterators.html#Defining-Mode-Iterators">Defining Mode Iterators</a>.
</p>
<p>It is possible to define attributes for codes as well as for modes.
There are two standard code attributes: <code>code</code>, the name of the
code in lower case, and <code>CODE</code>, the name of the code in upper case.
Other attributes are defined using:
</p>
<div class="smallexample">
<pre class="smallexample">(define_code_attr <var>name</var> [(<var>code1</var> &quot;<var>value1</var>&quot;) &hellip; (<var>coden</var> &quot;<var>valuen</var>&quot;)])
</pre></div>

<p>Instruction patterns can use code attributes as rtx codes, which can be
useful if two sets of codes act in tandem.  For example, the following
<code>define_insn</code> defines two patterns, one calculating a signed absolute
difference and another calculating an unsigned absolute difference:
</p>
<div class="smallexample">
<pre class="smallexample">(define_code_iterator any_max [smax umax])
(define_code_attr paired_min [(smax &quot;smin&quot;) (umax &quot;umin&quot;)])
(define_insn &hellip;
  [(set (match_operand:SI 0 &hellip;)
        (minus:SI (any_max:SI (match_operand:SI 1 &hellip;)
                              (match_operand:SI 2 &hellip;))
                  (&lt;paired_min&gt;:SI (match_dup 1) (match_dup 2))))]
  &hellip;)
</pre></div>

<p>The signed version of the instruction uses <code>smax</code> and <code>smin</code>
while the unsigned version uses <code>umax</code> and <code>umin</code>.  There
are no versions that pair <code>smax</code> with <code>umin</code> or <code>umax</code>
with <code>smin</code>.
</p>
<p>Here&rsquo;s an example of code iterators in action, taken from the MIPS port:
</p>
<div class="smallexample">
<pre class="smallexample">(define_code_iterator any_cond [unordered ordered unlt unge uneq ltgt unle ungt
                                eq ne gt ge lt le gtu geu ltu leu])

(define_expand &quot;b&lt;code&gt;&quot;
  [(set (pc)
        (if_then_else (any_cond:CC (cc0)
                                   (const_int 0))
                      (label_ref (match_operand 0 &quot;&quot;))
                      (pc)))]
  &quot;&quot;
{
  gen_conditional_branch (operands, &lt;CODE&gt;);
  DONE;
})
</pre></div>

<p>This is equivalent to:
</p>
<div class="smallexample">
<pre class="smallexample">(define_expand &quot;bunordered&quot;
  [(set (pc)
        (if_then_else (unordered:CC (cc0)
                                    (const_int 0))
                      (label_ref (match_operand 0 &quot;&quot;))
                      (pc)))]
  &quot;&quot;
{
  gen_conditional_branch (operands, UNORDERED);
  DONE;
})

(define_expand &quot;bordered&quot;
  [(set (pc)
        (if_then_else (ordered:CC (cc0)
                                  (const_int 0))
                      (label_ref (match_operand 0 &quot;&quot;))
                      (pc)))]
  &quot;&quot;
{
  gen_conditional_branch (operands, ORDERED);
  DONE;
})

&hellip;
</pre></div>

<hr>
<div class="header">
<p>
Next: <a href="Int-Iterators.html#Int-Iterators" accesskey="n" rel="next">Int Iterators</a>, Previous: <a href="Mode-Iterators.html#Mode-Iterators" accesskey="p" rel="prev">Mode Iterators</a>, Up: <a href="Iterators.html#Iterators" accesskey="u" rel="up">Iterators</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>