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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/Constant-Definitions.html | |
https://developer.arm.com/downloads/-/arm-gnu-toolchain-downloads
Change-Id: I7303388733328cd98ab9aa3c30236db67f2e9e9c
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diff --git a/share/doc/gccint/Constant-Definitions.html b/share/doc/gccint/Constant-Definitions.html new file mode 100644 index 0000000..551d267 --- /dev/null +++ b/share/doc/gccint/Constant-Definitions.html @@ -0,0 +1,261 @@ +<!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: Constant Definitions</title> + +<meta name="description" content="GNU Compiler Collection (GCC) Internals: Constant Definitions"> +<meta name="keywords" content="GNU Compiler Collection (GCC) Internals: Constant Definitions"> +<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="Machine-Desc.html#Machine-Desc" rel="up" title="Machine Desc"> +<link href="Iterators.html#Iterators" rel="next" title="Iterators"> +<link href="Define-Subst-Output-Template.html#Define-Subst-Output-Template" rel="previous" title="Define Subst Output Template"> +<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="Constant-Definitions"></a> +<div class="header"> +<p> +Next: <a href="Iterators.html#Iterators" accesskey="n" rel="next">Iterators</a>, Previous: <a href="Define-Subst.html#Define-Subst" accesskey="p" rel="previous">Define Subst</a>, Up: <a href="Machine-Desc.html#Machine-Desc" accesskey="u" rel="up">Machine Desc</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="Constant-Definitions-1"></a> +<h3 class="section">17.22 Constant Definitions</h3> +<a name="index-constant-definitions"></a> +<a name="index-define_005fconstants"></a> + +<p>Using literal constants inside instruction patterns reduces legibility and +can be a maintenance problem. +</p> +<p>To overcome this problem, you may use the <code>define_constants</code> +expression. It contains a vector of name-value pairs. From that +point on, wherever any of the names appears in the MD file, it is as +if the corresponding value had been written instead. You may use +<code>define_constants</code> multiple times; each appearance adds more +constants to the table. It is an error to redefine a constant with +a different value. +</p> +<p>To come back to the a29k load multiple example, instead of +</p> +<div class="smallexample"> +<pre class="smallexample">(define_insn "" + [(match_parallel 0 "load_multiple_operation" + [(set (match_operand:SI 1 "gpc_reg_operand" "=r") + (match_operand:SI 2 "memory_operand" "m")) + (use (reg:SI 179)) + (clobber (reg:SI 179))])] + "" + "loadm 0,0,%1,%2") +</pre></div> + +<p>You could write: +</p> +<div class="smallexample"> +<pre class="smallexample">(define_constants [ + (R_BP 177) + (R_FC 178) + (R_CR 179) + (R_Q 180) +]) + +(define_insn "" + [(match_parallel 0 "load_multiple_operation" + [(set (match_operand:SI 1 "gpc_reg_operand" "=r") + (match_operand:SI 2 "memory_operand" "m")) + (use (reg:SI R_CR)) + (clobber (reg:SI R_CR))])] + "" + "loadm 0,0,%1,%2") +</pre></div> + +<p>The constants that are defined with a define_constant are also output +in the insn-codes.h header file as #defines. +</p> +<a name="index-enumerations"></a> +<a name="index-define_005fc_005fenum"></a> +<p>You can also use the machine description file to define enumerations. +Like the constants defined by <code>define_constant</code>, these enumerations +are visible to both the machine description file and the main C code. +</p> +<p>The syntax is as follows: +</p> +<div class="smallexample"> +<pre class="smallexample">(define_c_enum "<var>name</var>" [ + <var>value0</var> + <var>value1</var> + (<var>value32</var> 32) + <var>value33</var> + … + <var>valuen</var> +]) +</pre></div> + +<p>This definition causes the equivalent of the following C code to appear +in <samp>insn-constants.h</samp>: +</p> +<div class="smallexample"> +<pre class="smallexample">enum <var>name</var> { + <var>value0</var> = 0, + <var>value1</var> = 1, + <var>value32</var> = 32, + <var>value33</var> = 33, + … + <var>valuen</var> = <var>n</var> +}; +#define NUM_<var>cname</var>_VALUES (<var>n</var> + 1) +</pre></div> + +<p>where <var>cname</var> is the capitalized form of <var>name</var>. +It also makes each <var>valuei</var> available in the machine description +file, just as if it had been declared with: +</p> +<div class="smallexample"> +<pre class="smallexample">(define_constants [(<var>valuei</var> <var>i</var>)]) +</pre></div> + +<p>Each <var>valuei</var> is usually an upper-case identifier and usually +begins with <var>cname</var>. +</p> +<p>You can split the enumeration definition into as many statements as +you like. The above example is directly equivalent to: +</p> +<div class="smallexample"> +<pre class="smallexample">(define_c_enum "<var>name</var>" [<var>value0</var>]) +(define_c_enum "<var>name</var>" [<var>value1</var>]) +… +(define_c_enum "<var>name</var>" [<var>valuen</var>]) +</pre></div> + +<p>Splitting the enumeration helps to improve the modularity of each +individual <code>.md</code> file. For example, if a port defines its +synchronization instructions in a separate <samp>sync.md</samp> file, +it is convenient to define all synchronization-specific enumeration +values in <samp>sync.md</samp> rather than in the main <samp>.md</samp> file. +</p> +<p>Some enumeration names have special significance to GCC: +</p> +<dl compact="compact"> +<dd><a name="index-unspec_005fvolatile-1"></a> +</dd> +<dt><code>unspecv</code></dt> +<dd><p>If an enumeration called <code>unspecv</code> is defined, GCC will use it +when printing out <code>unspec_volatile</code> expressions. For example: +</p> +<div class="smallexample"> +<pre class="smallexample">(define_c_enum "unspecv" [ + UNSPECV_BLOCKAGE +]) +</pre></div> + +<p>causes GCC to print ‘<samp>(unspec_volatile … 0)</samp>’ as: +</p> +<div class="smallexample"> +<pre class="smallexample">(unspec_volatile ... UNSPECV_BLOCKAGE) +</pre></div> + +<a name="index-unspec-1"></a> +</dd> +<dt><code>unspec</code></dt> +<dd><p>If an enumeration called <code>unspec</code> is defined, GCC will use +it when printing out <code>unspec</code> expressions. GCC will also use +it when printing out <code>unspec_volatile</code> expressions unless an +<code>unspecv</code> enumeration is also defined. You can therefore +decide whether to keep separate enumerations for volatile and +non-volatile expressions or whether to use the same enumeration +for both. +</p></dd> +</dl> + +<a name="index-define_005fenum"></a> +<a name="define_005fenum"></a><p>Another way of defining an enumeration is to use <code>define_enum</code>: +</p> +<div class="smallexample"> +<pre class="smallexample">(define_enum "<var>name</var>" [ + <var>value0</var> + <var>value1</var> + … + <var>valuen</var> +]) +</pre></div> + +<p>This directive implies: +</p> +<div class="smallexample"> +<pre class="smallexample">(define_c_enum "<var>name</var>" [ + <var>cname</var>_<var>cvalue0</var> + <var>cname</var>_<var>cvalue1</var> + … + <var>cname</var>_<var>cvaluen</var> +]) +</pre></div> + +<a name="index-define_005fenum_005fattr-1"></a> +<p>where <var>cvaluei</var> is the capitalized form of <var>valuei</var>. +However, unlike <code>define_c_enum</code>, the enumerations defined +by <code>define_enum</code> can be used in attribute specifications +(see <a href="Defining-Attributes.html#define_005fenum_005fattr">define_enum_attr</a>). +</p><hr> +<div class="header"> +<p> +Next: <a href="Iterators.html#Iterators" accesskey="n" rel="next">Iterators</a>, Previous: <a href="Define-Subst.html#Define-Subst" accesskey="p" rel="previous">Define Subst</a>, Up: <a href="Machine-Desc.html#Machine-Desc" accesskey="u" rel="up">Machine Desc</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> |