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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/gcc/C_002b_002b-Modules.html | |
https://developer.arm.com/downloads/-/arm-gnu-toolchain-downloads
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diff --git a/share/doc/gcc/C_002b_002b-Modules.html b/share/doc/gcc/C_002b_002b-Modules.html new file mode 100644 index 0000000..fac0f7c --- /dev/null +++ b/share/doc/gcc/C_002b_002b-Modules.html @@ -0,0 +1,227 @@ +<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd"> +<html> +<!-- This file documents the use of the GNU compilers. + +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>Using the GNU Compiler Collection (GCC): C++ Modules</title> + +<meta name="description" content="Using the GNU Compiler Collection (GCC): C++ Modules"> +<meta name="keywords" content="Using the GNU Compiler Collection (GCC): C++ Modules"> +<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="Indices.html#Indices" rel="index" title="Indices"> +<link href="index.html#SEC_Contents" rel="contents" title="Table of Contents"> +<link href="Invoking-GCC.html#Invoking-GCC" rel="up" title="Invoking GCC"> +<link href="C_002b_002b-Module-Mapper.html#C_002b_002b-Module-Mapper" rel="next" title="C++ Module Mapper"> +<link href="Precompiled-Headers.html#Precompiled-Headers" rel="previous" title="Precompiled Headers"> +<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_US" bgcolor="#FFFFFF" text="#000000" link="#0000FF" vlink="#800080" alink="#FF0000"> +<a name="C_002b_002b-Modules"></a> +<div class="header"> +<p> +Previous: <a href="Precompiled-Headers.html#Precompiled-Headers" accesskey="p" rel="previous">Precompiled Headers</a>, Up: <a href="Invoking-GCC.html#Invoking-GCC" accesskey="u" rel="up">Invoking GCC</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Indices.html#Indices" title="Index" rel="index">Index</a>]</p> +</div> +<hr> +<a name="C_002b_002b-Modules-1"></a> +<h3 class="section">3.23 C++ Modules</h3> +<a name="index-speed-of-compilation-1"></a> + +<p>Modules are a C++20 language feature. As the name suggests, they +provides a modular compilation system, intending to provide both +faster builds and better library isolation. The “Merging Modules” +paper <a href="https://wg21.link/p1103">https://wg21.link/p1103</a>, provides the easiest to read set +of changes to the standard, although it does not capture later +changes. +</p> +<p><em>G++’s modules support is not complete.</em> Other than bugs, the +known missing pieces are: +</p> +<dl compact="compact"> +<dt><em>Private Module Fragment</em></dt> +<dd><p>The Private Module Fragment is recognized, but an error is emitted. +</p> +</dd> +<dt><em>Partition definition visibility rules</em></dt> +<dd><p>Entities may be defined in implementation partitions, and those +definitions are not available outside of the module. This is not +implemented, and the definitions are available to extra-module use. +</p> +</dd> +<dt><em>Textual merging of reachable GM entities</em></dt> +<dd><p>Entities may be multiply defined across different header-units. +These must be de-duplicated, and this is implemented across imports, +or when an import redefines a textually-defined entity. However the +reverse is not implemented—textually redefining an entity that has +been defined in an imported header-unit. A redefinition error is +emitted. +</p> +</dd> +<dt><em>Translation-Unit local referencing rules</em></dt> +<dd><p>Papers p1815 (<a href="https://wg21.link/p1815">https://wg21.link/p1815</a>) and p2003 +(<a href="https://wg21.link/p2003">https://wg21.link/p2003</a>) add limitations on which entities an +exported region may reference (for instance, the entities an exported +template definition may reference). These are not fully implemented. +</p> +</dd> +<dt><em>Standard Library Header Units</em></dt> +<dd><p>The Standard Library is not provided as importable header units. If +you want to import such units, you must explicitly build them first. +If you do not do this with care, you may have multiple declarations, +which the module machinery must merge—compiler resource usage can be +affected by how you partition header files into header units. +</p> +</dd> +</dl> + +<p>Modular compilation is <em>not</em> enabled with just the +<samp>-std=c++20</samp> option. You must explicitly enable it with the +<samp>-fmodules-ts</samp> option. It is independent of the language +version selected, although in pre-C++20 versions, it is of course an +extension. +</p> +<p>No new source file suffixes are required or supported. If you wish to +use a non-standard suffix (see <a href="Overall-Options.html#Overall-Options">Overall Options</a>), you also need +to provide a <samp>-x c++</samp> option too.<a name="DOCF2" href="#FOOT2"><sup>2</sup></a> +</p> +<p>Compiling a module interface unit produces an additional output (to +the assembly or object file), called a Compiled Module Interface +(CMI). This encodes the exported declarations of the module. +Importing a module reads in the CMI. The import graph is a Directed +Acyclic Graph (DAG). You must build imports before the importer. +</p> +<p>Header files may themselves be compiled to header units, which are a +transitional ability aiming at faster compilation. The +<samp>-fmodule-header</samp> option is used to enable this, and implies +the <samp>-fmodules-ts</samp> option. These CMIs are named by the fully +resolved underlying header file, and thus may be a complete pathname +containing subdirectories. If the header file is found at an absolute +pathname, the CMI location is still relative to a CMI root directory. +</p> +<p>As header files often have no suffix, you commonly have to specify a +<samp>-x</samp> option to tell the compiler the source is a header file. +You may use <samp>-x c++-header</samp>, <samp>-x c++-user-header</samp> or +<samp>-x c++-system-header</samp>. When used in conjunction with +<samp>-fmodules-ts</samp>, these all imply an appropriate +<samp>-fmodule-header</samp> option. The latter two variants use the +user or system include path to search for the file specified. This +allows you to, for instance, compile standard library header files as +header units, without needing to know exactly where they are +installed. Specifying the language as one of these variants also +inhibits output of the object file, as header files have no associated +object file. +</p> +<p>The <samp>-fmodule-only</samp> option disables generation of the +associated object file for compiling a module interface. Only the CMI +is generated. This option is implied when using the +<samp>-fmodule-header</samp> option. +</p> +<p>The <samp>-flang-info-include-translate</samp> and +<samp>-flang-info-include-translate-not</samp> options notes whether +include translation occurs or not. With no argument, the first will +note all include translation. The second will note all +non-translations of include files not known to intentionally be +textual. With an argument, queries about include translation of a +header files with that particular trailing pathname are noted. You +may repeat this form to cover several different header files. This +option may be helpful in determining whether include translation is +happening—if it is working correctly, it behaves as if it isn’t +there at all. +</p> +<p>The <samp>-flang-info-module-cmi</samp> option can be used to determine +where the compiler is reading a CMI from. Without the option, the +compiler is silent when such a read is successful. This option has an +optional argument, which will restrict the notification to just the +set of named modules or header units specified. +</p> +<p>The <samp>-Winvalid-imported-macros</samp> option causes all imported macros +to be resolved at the end of compilation. Without this, imported +macros are only resolved when expanded or (re)defined. This option +detects conflicting import definitions for all macros. +</p> +<p>For details of the <samp>-fmodule-mapper</samp> family of options, +see <a href="C_002b_002b-Module-Mapper.html#C_002b_002b-Module-Mapper">C++ Module Mapper</a>. +</p> +<table class="menu" border="0" cellspacing="0"> +<tr><td align="left" valign="top">• <a href="C_002b_002b-Module-Mapper.html#C_002b_002b-Module-Mapper" accesskey="1">C++ Module Mapper</a>:</td><td> </td><td align="left" valign="top">Module Mapper +</td></tr> +<tr><td align="left" valign="top">• <a href="C_002b_002b-Module-Preprocessing.html#C_002b_002b-Module-Preprocessing" accesskey="2">C++ Module Preprocessing</a>:</td><td> </td><td align="left" valign="top">Module Preprocessing +</td></tr> +<tr><td align="left" valign="top">• <a href="C_002b_002b-Compiled-Module-Interface.html#C_002b_002b-Compiled-Module-Interface" accesskey="3">C++ Compiled Module Interface</a>:</td><td> </td><td align="left" valign="top">Compiled Module Interface +</td></tr> +</table> + +<div class="footnote"> +<hr> +<h4 class="footnotes-heading">Footnotes</h4> + +<h3><a name="FOOT2" href="#DOCF2">(2)</a></h3> +<p>Some users like to +distinguish module interface files with a new suffix, such as naming +the source <code>module.cppm</code>, which involves +teaching all tools about the new suffix. A different scheme, such as +naming <code>module-m.cpp</code> would be less invasive.</p> +</div> +<hr> +<div class="header"> +<p> +Previous: <a href="Precompiled-Headers.html#Precompiled-Headers" accesskey="p" rel="previous">Precompiled Headers</a>, Up: <a href="Invoking-GCC.html#Invoking-GCC" accesskey="u" rel="up">Invoking GCC</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Indices.html#Indices" title="Index" rel="index">Index</a>]</p> +</div> + + + +</body> +</html> |