diff options
Diffstat (limited to 'share/doc/gccint/Attr-Example.html')
| -rw-r--r-- | share/doc/gccint/Attr-Example.html | 141 |
1 files changed, 141 insertions, 0 deletions
diff --git a/share/doc/gccint/Attr-Example.html b/share/doc/gccint/Attr-Example.html new file mode 100644 index 0000000..517ad31 --- /dev/null +++ b/share/doc/gccint/Attr-Example.html @@ -0,0 +1,141 @@ +<!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: Attr Example</title> + +<meta name="description" content="GNU Compiler Collection (GCC) Internals: Attr Example"> +<meta name="keywords" content="GNU Compiler Collection (GCC) Internals: Attr Example"> +<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="previous" title="Tagging Insns"> +<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="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="previous">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="previous">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> |