You cannot select more than 25 topics
Topics must start with a letter or number, can include dashes ('-') and can be up to 35 characters long.
141 lines
6.5 KiB
HTML
141 lines
6.5 KiB
HTML
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
|
|
<html>
|
|
<!-- Copyright (C) 1988-2018 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 6.4, http://www.gnu.org/software/texinfo/ -->
|
|
<head>
|
|
<title>Attr Example (GNU Compiler Collection (GCC) Internals)</title>
|
|
|
|
<meta name="description" content="Attr Example (GNU Compiler Collection (GCC) Internals)">
|
|
<meta name="keywords" content="Attr Example (GNU Compiler Collection (GCC) Internals)">
|
|
<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="Insn-Attributes.html#Insn-Attributes" rel="up" title="Insn Attributes">
|
|
<link href="Insn-Lengths.html#Insn-Lengths" rel="next" title="Insn Lengths">
|
|
<link href="Tagging-Insns.html#Tagging-Insns" rel="prev" title="Tagging Insns">
|
|
<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="Attr-Example"></a>
|
|
<div class="header">
|
|
<p>
|
|
Next: <a href="Insn-Lengths.html#Insn-Lengths" accesskey="n" rel="next">Insn Lengths</a>, Previous: <a href="Tagging-Insns.html#Tagging-Insns" accesskey="p" rel="prev">Tagging Insns</a>, Up: <a href="Insn-Attributes.html#Insn-Attributes" accesskey="u" rel="up">Insn Attributes</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="Example-of-Attribute-Specifications"></a>
|
|
<h4 class="subsection">17.19.4 Example of Attribute Specifications</h4>
|
|
<a name="index-attribute-specifications-example"></a>
|
|
<a name="index-attribute-specifications"></a>
|
|
|
|
<p>The judicious use of defaulting is important in the efficient use of
|
|
insn attributes. Typically, insns are divided into <em>types</em> and an
|
|
attribute, customarily called <code>type</code>, is used to represent this
|
|
value. This attribute is normally used only to define the default value
|
|
for other attributes. An example will clarify this usage.
|
|
</p>
|
|
<p>Assume we have a RISC machine with a condition code and in which only
|
|
full-word operations are performed in registers. Let us assume that we
|
|
can divide all insns into loads, stores, (integer) arithmetic
|
|
operations, floating point operations, and branches.
|
|
</p>
|
|
<p>Here we will concern ourselves with determining the effect of an insn on
|
|
the condition code and will limit ourselves to the following possible
|
|
effects: The condition code can be set unpredictably (clobbered), not
|
|
be changed, be set to agree with the results of the operation, or only
|
|
changed if the item previously set into the condition code has been
|
|
modified.
|
|
</p>
|
|
<p>Here is part of a sample <samp>md</samp> file for such a machine:
|
|
</p>
|
|
<div class="smallexample">
|
|
<pre class="smallexample">(define_attr "type" "load,store,arith,fp,branch" (const_string "arith"))
|
|
|
|
(define_attr "cc" "clobber,unchanged,set,change0"
|
|
(cond [(eq_attr "type" "load")
|
|
(const_string "change0")
|
|
(eq_attr "type" "store,branch")
|
|
(const_string "unchanged")
|
|
(eq_attr "type" "arith")
|
|
(if_then_else (match_operand:SI 0 "" "")
|
|
(const_string "set")
|
|
(const_string "clobber"))]
|
|
(const_string "clobber")))
|
|
|
|
(define_insn ""
|
|
[(set (match_operand:SI 0 "general_operand" "=r,r,m")
|
|
(match_operand:SI 1 "general_operand" "r,m,r"))]
|
|
""
|
|
"@
|
|
move %0,%1
|
|
load %0,%1
|
|
store %0,%1"
|
|
[(set_attr "type" "arith,load,store")])
|
|
</pre></div>
|
|
|
|
<p>Note that we assume in the above example that arithmetic operations
|
|
performed on quantities smaller than a machine word clobber the condition
|
|
code since they will set the condition code to a value corresponding to the
|
|
full-word result.
|
|
</p>
|
|
<hr>
|
|
<div class="header">
|
|
<p>
|
|
Next: <a href="Insn-Lengths.html#Insn-Lengths" accesskey="n" rel="next">Insn Lengths</a>, Previous: <a href="Tagging-Insns.html#Tagging-Insns" accesskey="p" rel="prev">Tagging Insns</a>, Up: <a href="Insn-Attributes.html#Insn-Attributes" accesskey="u" rel="up">Insn Attributes</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>
|