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diff --git a/share/doc/gccint/Tree-overview.html b/share/doc/gccint/Tree-overview.html new file mode 100644 index 0000000..9dd11cd --- /dev/null +++ b/share/doc/gccint/Tree-overview.html @@ -0,0 +1,180 @@ +<!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: Tree overview</title> + +<meta name="description" content="GNU Compiler Collection (GCC) Internals: Tree overview"> +<meta name="keywords" content="GNU Compiler Collection (GCC) Internals: Tree overview"> +<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="GENERIC.html#GENERIC" rel="up" title="GENERIC"> +<link href="Macros-and-Functions.html#Macros-and-Functions" rel="next" title="Macros and Functions"> +<link href="Deficiencies.html#Deficiencies" rel="previous" title="Deficiencies"> +<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="Tree-overview"></a> +<div class="header"> +<p> +Next: <a href="Types.html#Types" accesskey="n" rel="next">Types</a>, Previous: <a href="Deficiencies.html#Deficiencies" accesskey="p" rel="previous">Deficiencies</a>, Up: <a href="GENERIC.html#GENERIC" accesskey="u" rel="up">GENERIC</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="Overview-1"></a> +<h3 class="section">11.2 Overview</h3> +<a name="index-tree"></a> +<a name="index-TREE_005fCODE"></a> + +<p>The central data structure used by the internal representation is the +<code>tree</code>. These nodes, while all of the C type <code>tree</code>, are of +many varieties. A <code>tree</code> is a pointer type, but the object to +which it points may be of a variety of types. From this point forward, +we will refer to trees in ordinary type, rather than in <code>this +font</code>, except when talking about the actual C type <code>tree</code>. +</p> +<p>You can tell what kind of node a particular tree is by using the +<code>TREE_CODE</code> macro. Many, many macros take trees as input and +return trees as output. However, most macros require a certain kind of +tree node as input. In other words, there is a type-system for trees, +but it is not reflected in the C type-system. +</p> +<p>For safety, it is useful to configure GCC with <samp>--enable-checking</samp>. +Although this results in a significant performance penalty (since all +tree types are checked at run-time), and is therefore inappropriate in a +release version, it is extremely helpful during the development process. +</p> +<p>Many macros behave as predicates. Many, although not all, of these +predicates end in ‘<samp>_P</samp>’. Do not rely on the result type of these +macros being of any particular type. You may, however, rely on the fact +that the type can be compared to <code>0</code>, so that statements like +</p><div class="smallexample"> +<pre class="smallexample">if (TEST_P (t) && !TEST_P (y)) + x = 1; +</pre></div> +<p>and +</p><div class="smallexample"> +<pre class="smallexample">int i = (TEST_P (t) != 0); +</pre></div> +<p>are legal. Macros that return <code>int</code> values now may be changed to +return <code>tree</code> values, or other pointers in the future. Even those +that continue to return <code>int</code> may return multiple nonzero codes +where previously they returned only zero and one. Therefore, you should +not write code like +</p><div class="smallexample"> +<pre class="smallexample">if (TEST_P (t) == 1) +</pre></div> +<p>as this code is not guaranteed to work correctly in the future. +</p> +<p>You should not take the address of values returned by the macros or +functions described here. In particular, no guarantee is given that the +values are lvalues. +</p> +<p>In general, the names of macros are all in uppercase, while the names of +functions are entirely in lowercase. There are rare exceptions to this +rule. You should assume that any macro or function whose name is made +up entirely of uppercase letters may evaluate its arguments more than +once. You may assume that a macro or function whose name is made up +entirely of lowercase letters will evaluate its arguments only once. +</p> +<p>The <code>error_mark_node</code> is a special tree. Its tree code is +<code>ERROR_MARK</code>, but since there is only ever one node with that code, +the usual practice is to compare the tree against +<code>error_mark_node</code>. (This test is just a test for pointer +equality.) If an error has occurred during front-end processing the +flag <code>errorcount</code> will be set. If the front end has encountered +code it cannot handle, it will issue a message to the user and set +<code>sorrycount</code>. When these flags are set, any macro or function +which normally returns a tree of a particular kind may instead return +the <code>error_mark_node</code>. Thus, if you intend to do any processing of +erroneous code, you must be prepared to deal with the +<code>error_mark_node</code>. +</p> +<p>Occasionally, a particular tree slot (like an operand to an expression, +or a particular field in a declaration) will be referred to as +“reserved for the back end”. These slots are used to store RTL when +the tree is converted to RTL for use by the GCC back end. However, if +that process is not taking place (e.g., if the front end is being hooked +up to an intelligent editor), then those slots may be used by the +back end presently in use. +</p> +<p>If you encounter situations that do not match this documentation, such +as tree nodes of types not mentioned here, or macros documented to +return entities of a particular kind that instead return entities of +some different kind, you have found a bug, either in the front end or in +the documentation. Please report these bugs as you would any other +bug. +</p> +<table class="menu" border="0" cellspacing="0"> +<tr><td align="left" valign="top">• <a href="Macros-and-Functions.html#Macros-and-Functions" accesskey="1">Macros and Functions</a>:</td><td> </td><td align="left" valign="top">Macros and functions that can be used with all trees. +</td></tr> +<tr><td align="left" valign="top">• <a href="Identifiers.html#Identifiers" accesskey="2">Identifiers</a>:</td><td> </td><td align="left" valign="top">The names of things. +</td></tr> +<tr><td align="left" valign="top">• <a href="Containers.html#Containers" accesskey="3">Containers</a>:</td><td> </td><td align="left" valign="top">Lists and vectors. +</td></tr> +</table> + + +<hr> +<div class="header"> +<p> +Next: <a href="Types.html#Types" accesskey="n" rel="next">Types</a>, Previous: <a href="Deficiencies.html#Deficiencies" accesskey="p" rel="previous">Deficiencies</a>, Up: <a href="GENERIC.html#GENERIC" accesskey="u" rel="up">GENERIC</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> |