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| author | alk3pInjection <webmaster@raspii.tech> | 2024-02-04 16:16:35 +0800 |
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| committer | alk3pInjection <webmaster@raspii.tech> | 2024-02-04 16:16:35 +0800 |
| commit | abdaadbcae30fe0c9a66c7516798279fdfd97750 (patch) | |
| tree | 00a54a6e25601e43876d03c1a4a12a749d4a914c /share/doc/gccint/Defining-Attributes.html | |
https://developer.arm.com/downloads/-/arm-gnu-toolchain-downloads
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diff --git a/share/doc/gccint/Defining-Attributes.html b/share/doc/gccint/Defining-Attributes.html new file mode 100644 index 0000000..b8b9edb --- /dev/null +++ b/share/doc/gccint/Defining-Attributes.html @@ -0,0 +1,219 @@ +<!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: Defining Attributes</title> + +<meta name="description" content="GNU Compiler Collection (GCC) Internals: Defining Attributes"> +<meta name="keywords" content="GNU Compiler Collection (GCC) Internals: Defining Attributes"> +<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="Expressions.html#Expressions" rel="next" title="Expressions"> +<link href="Insn-Attributes.html#Insn-Attributes" rel="previous" title="Insn Attributes"> +<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="Defining-Attributes"></a> +<div class="header"> +<p> +Next: <a href="Expressions.html#Expressions" accesskey="n" rel="next">Expressions</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="Defining-Attributes-and-their-Values"></a> +<h4 class="subsection">17.19.1 Defining Attributes and their Values</h4> +<a name="index-defining-attributes-and-their-values"></a> +<a name="index-attributes_002c-defining"></a> + +<a name="index-define_005fattr"></a> +<p>The <code>define_attr</code> expression is used to define each attribute required +by the target machine. It looks like: +</p> +<div class="smallexample"> +<pre class="smallexample">(define_attr <var>name</var> <var>list-of-values</var> <var>default</var>) +</pre></div> + +<p><var>name</var> is a string specifying the name of the attribute being +defined. Some attributes are used in a special way by the rest of the +compiler. The <code>enabled</code> attribute can be used to conditionally +enable or disable insn alternatives (see <a href="Disable-Insn-Alternatives.html#Disable-Insn-Alternatives">Disable Insn Alternatives</a>). The <code>predicable</code> attribute, together with a +suitable <code>define_cond_exec</code> (see <a href="Conditional-Execution.html#Conditional-Execution">Conditional Execution</a>), can +be used to automatically generate conditional variants of instruction +patterns. The <code>mnemonic</code> attribute can be used to check for the +instruction mnemonic (see <a href="Mnemonic-Attribute.html#Mnemonic-Attribute">Mnemonic Attribute</a>). The compiler +internally uses the names <code>ce_enabled</code> and <code>nonce_enabled</code>, +so they should not be used elsewhere as alternative names. +</p> +<p><var>list-of-values</var> is either a string that specifies a comma-separated +list of values that can be assigned to the attribute, or a null string to +indicate that the attribute takes numeric values. +</p> +<p><var>default</var> is an attribute expression that gives the value of this +attribute for insns that match patterns whose definition does not include +an explicit value for this attribute. See <a href="Attr-Example.html#Attr-Example">Attr Example</a>, for more +information on the handling of defaults. See <a href="Constant-Attributes.html#Constant-Attributes">Constant Attributes</a>, +for information on attributes that do not depend on any particular insn. +</p> +<a name="index-insn_002dattr_002eh"></a> +<p>For each defined attribute, a number of definitions are written to the +<samp>insn-attr.h</samp> file. For cases where an explicit set of values is +specified for an attribute, the following are defined: +</p> +<ul> +<li> A ‘<samp>#define</samp>’ is written for the symbol ‘<samp>HAVE_ATTR_<var>name</var></samp>’. + +</li><li> An enumerated class is defined for ‘<samp>attr_<var>name</var></samp>’ with +elements of the form ‘<samp><var>upper-name</var>_<var>upper-value</var></samp>’ where +the attribute name and value are first converted to uppercase. + +</li><li> A function ‘<samp>get_attr_<var>name</var></samp>’ is defined that is passed an insn and +returns the attribute value for that insn. +</li></ul> + +<p>For example, if the following is present in the <samp>md</samp> file: +</p> +<div class="smallexample"> +<pre class="smallexample">(define_attr "type" "branch,fp,load,store,arith" …) +</pre></div> + +<p>the following lines will be written to the file <samp>insn-attr.h</samp>. +</p> +<div class="smallexample"> +<pre class="smallexample">#define HAVE_ATTR_type 1 +enum attr_type {TYPE_BRANCH, TYPE_FP, TYPE_LOAD, + TYPE_STORE, TYPE_ARITH}; +extern enum attr_type get_attr_type (); +</pre></div> + +<p>If the attribute takes numeric values, no <code>enum</code> type will be +defined and the function to obtain the attribute’s value will return +<code>int</code>. +</p> +<p>There are attributes which are tied to a specific meaning. These +attributes are not free to use for other purposes: +</p> +<dl compact="compact"> +<dt><code>length</code></dt> +<dd><p>The <code>length</code> attribute is used to calculate the length of emitted +code chunks. This is especially important when verifying branch +distances. See <a href="Insn-Lengths.html#Insn-Lengths">Insn Lengths</a>. +</p> +</dd> +<dt><code>enabled</code></dt> +<dd><p>The <code>enabled</code> attribute can be defined to prevent certain +alternatives of an insn definition from being used during code +generation. See <a href="Disable-Insn-Alternatives.html#Disable-Insn-Alternatives">Disable Insn Alternatives</a>. +</p> +</dd> +<dt><code>mnemonic</code></dt> +<dd><p>The <code>mnemonic</code> attribute can be defined to implement instruction +specific checks in e.g. the pipeline description. +See <a href="Mnemonic-Attribute.html#Mnemonic-Attribute">Mnemonic Attribute</a>. +</p></dd> +</dl> + +<p>For each of these special attributes, the corresponding +‘<samp>HAVE_ATTR_<var>name</var></samp>’ ‘<samp>#define</samp>’ is also written when the +attribute is not defined; in that case, it is defined as ‘<samp>0</samp>’. +</p> +<a name="index-define_005fenum_005fattr"></a> +<a name="define_005fenum_005fattr"></a><p>Another way of defining an attribute is to use: +</p> +<div class="smallexample"> +<pre class="smallexample">(define_enum_attr "<var>attr</var>" "<var>enum</var>" <var>default</var>) +</pre></div> + +<p>This works in just the same way as <code>define_attr</code>, except that +the list of values is taken from a separate enumeration called +<var>enum</var> (see <a href="Constant-Definitions.html#define_005fenum">define_enum</a>). This form allows you to use +the same list of values for several attributes without having to +repeat the list each time. For example: +</p> +<div class="smallexample"> +<pre class="smallexample">(define_enum "processor" [ + model_a + model_b + … +]) +(define_enum_attr "arch" "processor" + (const (symbol_ref "target_arch"))) +(define_enum_attr "tune" "processor" + (const (symbol_ref "target_tune"))) +</pre></div> + +<p>defines the same attributes as: +</p> +<div class="smallexample"> +<pre class="smallexample">(define_attr "arch" "model_a,model_b,…" + (const (symbol_ref "target_arch"))) +(define_attr "tune" "model_a,model_b,…" + (const (symbol_ref "target_tune"))) +</pre></div> + +<p>but without duplicating the processor list. The second example defines two +separate C enums (<code>attr_arch</code> and <code>attr_tune</code>) whereas the first +defines a single C enum (<code>processor</code>). +</p><hr> +<div class="header"> +<p> +Next: <a href="Expressions.html#Expressions" accesskey="n" rel="next">Expressions</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> |