GNU Compiler Collection: Difference between revisions

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The '''GNU Compiler Collection''' ('''GCC''') is a collection of [[compiler]]s from the [[GNU Project]] that support various [[programming language]]s, [[Computer architecture|hardware architectures]], and [[operating system]]s. The [[Free Software Foundation]] (FSF) distributes GCC as [[free software]] under the [[GNU General Public License]] (GNU GPL). GCC is a key component of the [[GNU toolchain]] which is used for most projects related to [[GNU]] and the [[Linux kernel]]. With roughly 15 million lines of code in 2019, GCC is one of the largest free programs in existence.<ref name="loc"/> It has played an important role in the growth of [[free software]], as both a tool and an example.

When it was first released in 1987 by [[Richard Stallman]], GCC 1.0 was named the '''GNU C Compiler''' since it only handled the [[C (programming language)|C programming language]].<ref name="release-history" /> It was extended to compile [[C++]] in December of that year. [[Compiler#Front end|Front ends]] were later developed for [[Objective-C]], [[Objective-C++]], [[Fortran]], [[Ada (programming language)|Ada]], [[Go (programming language)|Go]], [[D (programming language)|D]], [[Modula-2]], [[Rust (programming language)|Rust]] and [[COBOL]] among others.<ref>{{cite web|url=https://gcc.gnu.org/frontends.html|title=Programming Languages Supported by GCC|access-date=2014-06-23|publisher=GNU Project|archive-date=January 18, 2023|archive-url=https://web.archive.org/web/20230118185814/https://gcc.gnu.org/frontends.html|url-status=live}}</ref> The [[OpenMP]] and [[OpenACC]] specifications are also supported in the C and C++ compilers.<ref name="gcc6">{{Cite web|url=https://gcc.gnu.org/gcc-6/changes.html|title=GCC 6 Release Series — Changes, New Features, and Fixes - GNU Project|website=gcc.gnu.org|access-date=September 19, 2016|archive-date=September 22, 2016|archive-url=https://web.archive.org/web/20160922161533/http://gcc.gnu.org/gcc-6/changes.html|url-status=live}}</ref><ref name=":2">{{Cite web|url=https://gcc.gnu.org/wiki/OpenACC|title=OpenACC - GCC Wiki|website=gcc.gnu.org|access-date=September 19, 2016|archive-date=April 1, 2015|archive-url=https://web.archive.org/web/20150401174332/https://gcc.gnu.org/wiki/OpenACC|url-status=live}}</ref>

In late 1983, in an effort to [[Bootstrapping (compilers)|bootstrap]] the [[GNU]] operating system, [[Richard Stallman]] asked [[Andrew S. Tanenbaum]], the author of the [[Amsterdam Compiler Kit]] (also known as the ''[[Vrije Universiteit Amsterdam|Free University]]'' ''Compiler Kit''), for permission to use that software for GNU. When Tanenbaum advised him that the compiler was not free, and that only the university was free, Stallman decided to work on a different compiler.<ref>{{cite book |last=von Hagen |first=William |date=2006 |title=The Definitive Guide to GCC |edition=2nd |series=Definitive Guides |publisher=Apress |isbn=978-1-4302-0219-6 |page=XXVII |quote=So he wrote to VUCK's author asking if GNU could use it. Evidently, VUCK's developer was uncooperative, responding that the university was free but that the compiler was not. |url=https://books.google.com/books?id=wQ6r3UTivJgC |access-date=September 25, 2020 |archive-date=April 5, 2024 |archive-url=https://web.archive.org/web/20240405040135/https://books.google.com/books?id=wQ6r3UTivJgC |url-status=live }}</ref> His initial plan was to rewrite an existing compiler from [[Lawrence Livermore National Laboratory]] from [[Pastel (programming language)|Pastel]] to C with some help from [[Leonard H. Tower Jr.|Len Tower]] and others.<ref name=LLLCompiler>{{cite web | last = Stallman | first = Richard | title = About the GNU Project | publisher = The GNU Project | date = September 20, 2011 | url = https://www.gnu.org/gnu/thegnuproject.html | access-date = October 9, 2011 | archive-date = August 9, 2019 | archive-url = https://web.archive.org/web/20190809050636/http://www.gnu.org/gnu/thegnuproject.html | url-status = live }}</ref><ref>{{cite journal | editor-last = Puzo | editor-first = Jerome E. | title = Gnu's Zoo | journal = GNU's Bulletin | volume = 1 | issue = 1 | date = February 1986 | publisher = Free Software Foundation | url = https://www.gnu.org/bulletins/bull1.txt | access-date = 2007-08-11 | archive-date = June 23, 2015 | archive-url = https://web.archive.org/web/20150623180723/http://www.gnu.org/bulletins/bull1.txt | url-status = live }}</ref> Stallman wrote a new C front end for the Livermore compiler, but then realized that it required megabytes of stack space, an impossibility on a [[Motorola 68000|68000]] Unix system with only 64&nbsp;KB, and concluded he would have to write a new compiler from scratch.<ref name=LLLCompiler /> None of the Pastel compiler code ended up in GCC, though Stallman did use the C front end he had written.<ref name=LLLCompiler /><ref name=":6">{{cite book |last=von Hagen |first=William |date=2006 |title=The Definitive Guide to GCC |edition=2nd |series=Definitive Guides |publisher=Apress |isbn=978-1-4302-0219-6 |page=XXVII |url=https://books.google.com/books?id=wQ6r3UTivJgC |access-date=September 25, 2020 |archive-date=April 5, 2024 |archive-url=https://web.archive.org/web/20240405040135/https://books.google.com/books?id=wQ6r3UTivJgC |url-status=live }}</ref>

{{As of|alt=As of the 15.1 release| 2023|04|post=,}} GCC includes front ends for [[C (programming language)|C]] (<code>gcc</code>), [[C++]] (<code>g++</code>), [[Objective-C]], [[Objective-C#Objective-C++|Objective-C++]], [[Fortran]] (<code>[[gfortran]]</code>), [[Ada (programming language)|Ada]] ([[GNAT]]), [[Go (programming language)|Go]] (<code>gccgo</code>), [[D (programming language)|D]] (<code>gdc</code>, since 9.1),<ref>{{cite web | url=https://gcc.gnu.org/gcc-9/changes.html#d | title=GCC 9 Release Series — Changes, New Features, and Fixes - GNU Project | access-date=May 7, 2019 | archive-date=February 19, 2022 | archive-url=https://web.archive.org/web/20220219120525/https://gcc.gnu.org/gcc-9/changes.html#d | url-status=live }}</ref><ref>{{Cite web|title=The D Language Front-End Finally Merged Into GCC 9 - Phoronix|url=https://phoronix.com/scan.php?page=news_item&px=GCC-9-Merges-D-Language|access-date=2021-01-19|website=phoronix.com|archive-date=May 17, 2022|archive-url=https://web.archive.org/web/20220517184343/https://www.phoronix.com/scan.php?page=news_item&px=GCC-9-Merges-D-Language|url-status=live}}</ref> [[Modula-2]] (<code>gm2</code>, since 13.1),<ref>{{cite web | url=https://gcc.gnu.org/gcc-13/changes.html#modula2 | title=GCC 13 Release Series — Changes, New Features, and Fixes - GNU Project | access-date=June 23, 2023 | archive-date=May 26, 2023 | archive-url=https://web.archive.org/web/20230526084642/http://gcc.gnu.org/gcc-13/changes.html#modula2 | url-status=live }}</ref><ref>{{Cite web |url=https://www.theregister.com/2022/12/16/gcc_13_will_support_modula2/ |title=GCC 13 to support Modula-2: Follow-up to Pascal lives on in FOSS form |date=2022-12-16 |access-date=2022-12-19 |last=Proven |first=Liam |archive-date=December 19, 2022 |archive-url=https://web.archive.org/web/20221219080641/https://www.theregister.com/2022/12/16/gcc_13_will_support_modula2/ |url-status=live }}</ref> [[Rust (programming language)|Rust]] (<code>gccrs</code>, since 15.1) and [[COBOL]] (<code>gcobol</code>, since 15.1) programming languages,<ref name=":7">{{cite web|url=https://gcc.gnu.org/frontends.html|title=GCC Front Ends|publisher=gnu.org|access-date=November 25, 2011|archive-date=January 18, 2023|archive-url=https://web.archive.org/web/20230118185814/https://gcc.gnu.org/frontends.html|url-status=live}}</ref> with the [[OpenMP]] and [[OpenACC]] parallel language extensions being supported since GCC 5.1.<ref name=":2" /><ref>{{Cite web|url=https://gcc.gnu.org/gcc-5/changes.html|title=GCC 5 Release Series — Changes, New Features, and Fixes - GNU Project|website=gcc.gnu.org|access-date=April 23, 2015|archive-date=January 18, 2023|archive-url=https://web.archive.org/web/20230118185814/https://gcc.gnu.org/gcc-5/changes.html|url-status=live}}</ref> Versions prior to GCC 7 also supported [[Java (programming language)|Java]] (<code>[[GNU Compiler for Java|gcj]]</code>), allowing compilation of Java to native machine code.<ref>{{cite web|title=GCC 7 Release Series|url=https://gcc.gnu.org/gcc-7/changes.html#java|access-date=March 20, 2018|publisher=gnu.org|archive-date=September 2, 2020|archive-url=https://web.archive.org/web/20200902223230/https://gcc.gnu.org/gcc-7/changes.html#java|url-status=live}}</ref>

Third-party front ends exist for many languages, such as [[ALGOL 68]],<ref>{{cite web |last1=E. Marchesi |first1=Jose |title= GCC Wiki: Algol 68 Front-End |url=https://gcc.gnu.org/wiki/Algol68FrontEnd |website=gcc.gnu.org}}</ref> [[Pascal (programming language)|Pascal]] (<code>[[GNU Pascal|gpc]]</code>), [[Mercury (programming language)|Mercury]], [[Modula-3]], [[VHDL]] (<code>GHDL</code>) and [[PL/I]].<ref name=":7" /> A few experimental branches exist to support additional languages, such as the GCC [[Unified Parallel C|UPC]] compiler for [[Unified Parallel C]].<ref>{{cite web|url=http://www.gccupc.org/|title=GCC UPC (GCC Unified Parallel C)|publisher=Intrepid Technology, Inc.|date=2006-02-20|access-date=2009-03-11|archive-date=February 11, 2010|archive-url=https://web.archive.org/web/20100211142352/http://www.gccupc.org/|url-status=dead}}</ref><ref>{{Cite web|last=Spengler|first=Brad|date=12 January 2021|title=Open Source Security, Inc. Announces Funding of GCC Front-End for Rust|url=https://opensrcsec.com/open_source_security_announces_rust_gcc_funding|access-date=|website=|archive-date=April 25, 2021|archive-url=https://web.archive.org/web/20210425170408/https://opensrcsec.com/open_source_security_announces_rust_gcc_funding|url-status=live}}</ref>{{Better source needed|date=January 2021}}

Regarding language version support for C++ and C, since GCC 11.1 the default target is ''gnu++17'', a superset of [[C++17]], and ''gnu11'', a superset of [[C11 (C standard revision)|C11]], with strict standard support also available. GCC also provides experimental support for [[C++20]] and [[C++23]].<ref>{{Cite web|title=C++ Standards Support in GCC|url=https://gcc.gnu.org/projects/cxx-status.html|access-date=May 17, 2021|archive-date=April 20, 2022|archive-url=https://web.archive.org/web/20220420114133/https://gcc.gnu.org/projects/cxx-status.html|url-status=live}}</ref>

In transforming the source code to GIMPLE,<ref>{{Cite web|url=https://gcc.gnu.org/onlinedocs/gccint/GIMPLE.html|title=GIMPLE (GNU Compiler Collection (GCC) Internals)|website=gcc.gnu.org|access-date=July 25, 2016|archive-date=January 18, 2023|archive-url=https://web.archive.org/web/20230118185814/https://gcc.gnu.org/onlinedocs/gccint/GIMPLE.html|url-status=live}}</ref> complex [[Expression (programming)|expressions]] are split into a [[three-address code]] using [[temporary variable]]s. This representation was inspired by the SIMPLE representation proposed in the McCAT compiler<ref>{{cite web |url=http://www-acaps.cs.mcgill.ca/info/McCAT/McCAT.html |title=McCAT |access-date=2017-09-14 |url-status=bot: unknown |archive-url=https://web.archive.org/web/20040812030043/http://www-acaps.cs.mcgill.ca/info/McCAT/McCAT.html |archive-date=August 12, 2004 |df=mdy-all }}</ref> by Laurie J. Hendren<ref>{{Cite web|url=http://www.sable.mcgill.ca/~hendren/|title=Laurie Hendren's Home Page|website=www.sable.mcgill.ca|access-date=July 20, 2009|archive-date=September 27, 2022|archive-url=https://web.archive.org/web/20220927074148/http://www.sable.mcgill.ca/~hendren/|url-status=live}}</ref> for simplifying the analysis and [[Optimization (computer science)|optimization]] of [[Imperative programming|imperative programs]].

The GCC project includes an implementation of the [[C++ Standard Library]] called libstdc++,<ref>{{cite web|url=https://gcc.gnu.org/onlinedocs/libstdc++|title=The GNU C++ Library|publisher=GNU Project|accessdate=2021-02-21|archive-date=December 25, 2022|archive-url=https://web.archive.org/web/20221225041607/https://gcc.gnu.org/onlinedocs/libstdc++/|url-status=live}}</ref> licensed under the GPLv3 License with an exception to link non-GPL applications when sources are built with GCC.<ref>{{cite web|url=https://gcc.gnu.org/onlinedocs/libstdc++/manual/license.html|title=License|publisher=GNU Project|accessdate=2021-02-21|archive-date=January 18, 2023|archive-url=https://web.archive.org/web/20230118185814/https://gcc.gnu.org/onlinedocs/libstdc++/manual/license.html|url-status=live}}</ref>

:* The MELT plugin provides a high-level [[Lisp (programming language)|Lisp]]-like language to extend GCC.<ref>{{cite web|title=About GCC MELT|url=http://gcc-melt.org/|access-date=July 8, 2013|archive-url= https://archive.today/20130704015544/http://gcc-melt.org/|archive-date=July 4, 2013|url-status=live}}</ref>

However this exception is limited. E.g. When non [[GNU General Public License|GPL]]-compatible software is used together with GCC within the [[Compiler|Compile Process]] follow the [[GNU General Public License|GPL]] for all of the propagated object code GCC generated becomes mandatory as it is derived from the [[GNU General Public License|GPL]]-licensed libraries.<ref>{{Cite web |title=GCC Runtime Library Exception Rationale and FAQ - GNU Project - Free Software Foundation |url=https://www.gnu.org/licenses/gcc-exception-3.1-faq.html |archive-url=http://web.archive.org/web/20250725141736/https://www.gnu.org/licenses/gcc-exception-3.1-faq.html |archive-date=2025-07-25 |access-date=2025-07-31 |website=www.gnu.org |publisher=[[Free Software Foundation]] |at=Section "How the Exception Works" |language=en |quote=How the Exception Works (...) You have permission to propagate a work of Target Code formed by combining the Runtime Library with Independent Modules, even if such propagation would otherwise violate the terms of GPLv3, provided that all Target Code was generated by Eligible Compilation Processes. You may then convey such a combination under terms of your choice, consistent with the licensing of the Independent Modules. (...) However, if you used GCC in conjunction with GPL-incompatible software during the process of transforming high-level code to low-level code, that would not be an Eligible Compilation Process. This would happen if, for example, you used GCC with a proprietary plugin. (...) As long as you use an Eligible Compilation Process, then you have permission to take the Target Code that GCC generates and propagate it “under terms of your choice.” If you did use GPL-incompatible software in conjunction with GCC during the Compilation Process, you would not be able to take advantage of this permission. Since all of the object code that GCC generates is derived from these GPLed libraries, that means you would be required to follow the terms of the GPL when propagating any of that object code. You could not use GCC to develop your own GPL-incompatible software.}}</ref>

* [http://www.cse.iitb.ac.in/grc/ Collection of GCC 4.0.2 architecture and internals documents] at I.I.T. Bombay

* {{cite news |date=March 2, 2006 |title=New GCC Heavy on Optimization |publisher= internetnews.com |last= Kerner |first=Sean Michael |url = http://www.internetnews.com/dev-news/article.php/3588926 |postscript=none}}

* {{cite news |date=April 22, 2005 |title=Open Source GCC 4.0: Older, Faster |publisher=internetnews.com |last=Kerner |first=Sean Michael |url=http://www.internetnews.com/dev-news/article.php/3499881 |postscript=none |access-date=October 21, 2006 |archive-date=September 17, 2006 |archive-url=https://web.archive.org/web/20060917233745/http://www.internetnews.com/dev-news/article.php/3499881 |url-status=dead }}

* [https://web.archive.org/web/20090401215553/http://www.redhat.com/magazine/002dec04/features/gcc/ From Source to Binary: The Inner Workings of GCC], by Diego Novillo, ''[[Red Hat#Opensource.com|Red Hat Magazine]]'', December 2004

* [http://gcc.gnu.org/pub/gcc/summit/2003/GENERIC%20and%20GIMPLE.pdf A 2003 paper on GENERIC and GIMPLE]

* [https://web.archive.org/web/20171022105307/http://www.toad.com/gnu/cygnus/index.html Marketing Cygnus Support], an essay covering GCC development for the 1990s, with 30 monthly reports for in the "Inside Cygnus Engineering" section near the end

* [http://oldhome.schmorp.de/egcs.html EGCS 1.0 announcement]

* [http://linuxmafia.com/faq/Licensing_and_Law/forking.html Fear of Forking], an essay by Rick Moen recording seven well-known forks, including the GCC/EGCS one