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84-594: The GNU Compiler Collection ( GCC ) is a collection of compilers from the GNU Project that support various programming languages , hardware architectures and operating systems . 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

168-533: A basic block , to whole procedures, or even the whole program. There is a trade-off between the granularity of the optimizations and the cost of compilation. For example, peephole optimizations are fast to perform during compilation but only affect a small local fragment of the code, and can be performed independently of the context in which the code fragment appears. In contrast, interprocedural optimization requires more compilation time and memory space, but enable optimizations that are only possible by considering

252-570: A compiler is a computer program that translates computer code written in one programming language (the source language) into another language (the target language). The name "compiler" is primarily used for programs that translate source code from a high-level programming language to a low-level programming language (e.g. assembly language , object code , or machine code ) to create an executable program. There are many different types of compilers which produce output in different useful forms. A cross-compiler produces code for

336-412: A concrete syntax tree (CST, parse tree) and then transforming it into an abstract syntax tree (AST, syntax tree). In some cases additional phases are used, notably line reconstruction and preprocessing, but these are rare. The main phases of the front end include the following: The middle end, also known as optimizer, performs optimizations on the intermediate representation in order to improve

420-429: A C++ compiler is required that understands ISO/IEC C++03 standard. On May 18, 2020, GCC moved away from ISO/IEC C++03 standard to ISO/IEC C++11 standard (i.e. needed to compile, bootstrap, the compiler itself; by default it however compiles later versions of C++). Each front end uses a parser to produce the abstract syntax tree of a given source file . Due to the syntax tree abstraction, source files of any of

504-422: A PDP-7 in B. Unics eventually became spelled Unix. Bell Labs started the development and expansion of C based on B and BCPL. The BCPL compiler had been transported to Multics by Bell Labs and BCPL was a preferred language at Bell Labs. Initially, a front-end program to Bell Labs' B compiler was used while a C compiler was developed. In 1971, a new PDP-11 provided the resource to define extensions to B and rewrite

588-437: A Production Quality Compiler (PQC) from formal definitions of source language and the target. PQCC tried to extend the term compiler-compiler beyond the traditional meaning as a parser generator (e.g., Yacc ) without much success. PQCC might more properly be referred to as a compiler generator. PQCC research into code generation process sought to build a truly automatic compiler-writing system. The effort discovered and designed

672-405: A compiler up into small programs is a technique used by researchers interested in producing provably correct compilers. Proving the correctness of a set of small programs often requires less effort than proving the correctness of a larger, single, equivalent program. Regardless of the exact number of phases in the compiler design, the phases can be assigned to one of three stages. The stages include

756-432: A component of an IDE (VADS, Eclipse, Ada Pro). The interrelationship and interdependence of technologies grew. The advent of web services promoted growth of web languages and scripting languages. Scripts trace back to the early days of Command Line Interfaces (CLI) where the user could enter commands to be executed by the system. User Shell concepts developed with languages to write shell programs. Early Windows designs offered

840-520: A different CPU or operating system than the one on which the cross-compiler itself runs. A bootstrap compiler is often a temporary compiler, used for compiling a more permanent or better optimised compiler for a language. Related software include decompilers , programs that translate from low-level languages to higher level ones; programs that translate between high-level languages, usually called source-to-source compilers or transpilers ; language rewriters , usually programs that translate

924-628: A front end, a middle end, and a back end. This front/middle/back-end approach makes it possible to combine front ends for different languages with back ends for different CPUs while sharing the optimizations of the middle end. Practical examples of this approach are the GNU Compiler Collection , Clang ( LLVM -based C/C++ compiler), and the Amsterdam Compiler Kit , which have multiple front-ends, shared optimizations and multiple back-ends. The front end analyzes

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1008-531: A front-end for CHILL due to a lack of maintenance. Before version 4.0 the Fortran front end was g77 , which only supported FORTRAN 77 , but later was dropped in favor of the new GNU Fortran front end that supports Fortran 95 and large parts of Fortran 2003 and Fortran 2008 as well. As of version 4.8, GCC is implemented in C++. Support for Cilk Plus existed from GCC 5 to GCC 7. GCC has been ported to

1092-527: A grammar for the language, though in more complex cases these require manual modification. The lexical grammar and phrase grammar are usually context-free grammars , which simplifies analysis significantly, with context-sensitivity handled at the semantic analysis phase. The semantic analysis phase is generally more complex and written by hand, but can be partially or fully automated using attribute grammars . These phases themselves can be further broken down: lexing as scanning and evaluating, and parsing as building

1176-645: A group of developers formed the Experimental/Enhanced GNU Compiler System (EGCS) to merge several experimental forks into a single project. The basis of the merger was a development snapshot of GCC (taken around the 2.7.2 and later followed up to 2.8.1 release). Mergers included g77 (Fortran), PGCC ( P5 Pentium -optimized GCC), many C++ improvements, and many new architectures and operating system variants. While both projects followed each other's changes closely, EGCS development proved considerably more vigorous, so much so that

1260-433: A language-specific driver program ( gcc for C, g++ for C++, etc.), which interprets command arguments , calls the actual compiler, runs the assembler on the output, and then optionally runs the linker to produce a complete executable binary. Each of the language compilers is a separate program that reads source code and outputs machine code . All have a common internal structure. A per-language front end parses

1344-446: A much more limited scope, and have less high-level information. Some of these optimizations performed at this level include dead-code elimination , partial-redundancy elimination , global value numbering , sparse conditional constant propagation , and scalar replacement of aggregates . Array dependence based optimizations such as automatic vectorization and automatic parallelization are also performed. Profile-guided optimization

1428-582: A new C front end for the Livermore compiler, but then realized that it required megabytes of stack space, an impossibility on a 68000 Unix system with only 64 KB, and concluded he would have to write a new compiler from scratch. None of the Pastel compiler code ended up in GCC, though Stallman did use the C front end he had written. GCC was first released March 22, 1987, available by FTP from MIT . Stallman

1512-432: A result, compilers were split up into smaller programs which each made a pass over the source (or some representation of it) performing some of the required analysis and translations. The ability to compile in a single pass has classically been seen as a benefit because it simplifies the job of writing a compiler and one-pass compilers generally perform compilations faster than multi-pass compilers . Thus, partly driven by

1596-431: A simple batch programming capability. The conventional transformation of these language used an interpreter. While not widely used, Bash and Batch compilers have been written. More recently sophisticated interpreted languages became part of the developers tool kit. Modern scripting languages include PHP, Python, Ruby and Lua. (Lua is widely used in game development.) All of these have interpreter and compiler support. "When

1680-594: A wide variety of instruction set architectures , and is widely deployed as a tool in the development of both free and proprietary software . GCC is also available for many embedded systems , including Symbian (called gcce ), ARM -based, and Power ISA -based chips. The compiler can target a wide variety of platforms, including video game consoles such as the PlayStation 2 , Cell SPE of PlayStation 3, and Dreamcast . It has been ported to more kinds of processors and operating systems than any other compiler. As of

1764-492: Is Open64 , which is used by many organizations for research and commercial purposes. Due to the extra time and space needed for compiler analysis and optimizations, some compilers skip them by default. Users have to use compilation options to explicitly tell the compiler which optimizations should be enabled. The back end is responsible for the CPU architecture specific optimizations and for code generation . The main phases of

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1848-399: Is 4.2, but much of the book still applies to this version. The major change since the book was published is in the code-generator interface, which is described in a separate document. The source code for LCC is around 20,000 lines, which is much smaller than many major compilers. LCC can generate code for several processor architectures, including Alpha , SPARC , MIPS , and x86 ; there

1932-574: Is a heavily modified version of LCC providing C11 as well as C17 support, amd64 support, additional optimisation techniques such as inline expansion and an IDE . For 32-bit Windows machines, Lcc is used as a default if no other compiler is installed for MathWorks MATLAB and related products. LCC is free for personal use and may be redistributed provided all distribution media and product documentation acknowledges it. The LCC license relies on examples in multiple cases. LCC may not be sold for profit, but it may be included with other software that

2016-423: Is a simplified GENERIC, in which various constructs are lowered to multiple GIMPLE instructions. The C , C++ , and Java front ends produce GENERIC directly in the front end. Other front ends instead have different intermediate representations after parsing and convert these to GENERIC. In either case, the so-called "gimplifier" then converts this more complex form into the simpler SSA -based GIMPLE form that

2100-414: Is also an LCC backend that generates Microsoft's Common Intermediate Language . id Software 's id Tech 3 engine relies on a modified version of LCC to compile the source code of each game module or third-party mod into bytecode targeting its virtual machine . This means that modules are oblivious to the system beyond the system calls and limited file system scope offered by the engine, which

2184-613: Is also commercial support, for example, AdaCore, was founded in 1994 to provide commercial software solutions for Ada. GNAT Pro includes the GNU GCC based GNAT with a tool suite to provide an integrated development environment . High-level languages continued to drive compiler research and development. Focus areas included optimization and automatic code generation. Trends in programming languages and development environments influenced compiler technology. More compilers became included in language distributions (PERL, Java Development Kit) and as

2268-649: Is also possible. The GCC project includes an implementation of the C++ Standard Library called libstdc++, licensed under the GPLv3 License with an exception to link non-GPL applications when sources are built with GCC. Some features of GCC include: The primary supported (and best tested) processor families are 64- and 32-bit ARM, 64- and 32-bit x86_64 and x86 and 64-bit PowerPC and SPARC . GCC target processor families as of version 11.1 include: Lesser-known target processors supported in

2352-446: Is favored due to its modularity and separation of concerns . Most commonly, the frontend is broken into three phases: lexical analysis (also known as lexing or scanning), syntax analysis (also known as scanning or parsing), and semantic analysis . Lexing and parsing comprise the syntactic analysis (word syntax and phrase syntax, respectively), and in simple cases, these modules (the lexer and parser) can be automatically generated from

2436-506: Is intended to reduce the threat posed by malicious mod authors. Another consideration is that games and mods written for the engine are portable without recompilation; only the virtual machine needs to be ported to new platforms in order to execute the modules. lcc-win32 is an integrated development environment package for Microsoft Windows which includes a fork of LCC. An amd64 counterpart named lcc-win64 exists, which has been available since April 15, 2012. Pelles C 's compiler

2520-442: Is the common language for a large number of powerful language- and architecture-independent global (function scope) optimizations. GENERIC is an intermediate representation language used as a "middle end" while compiling source code into executable binaries . A subset, called GIMPLE , is targeted by all the front ends of GCC. The middle stage of GCC does all of the code analysis and optimization , working independently of both

2604-624: The GNU operating system, Richard Stallman asked Andrew S. Tanenbaum , the author of the Amsterdam Compiler Kit (also known as the 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. His initial plan was to rewrite an existing compiler from Lawrence Livermore National Laboratory from Pastel to C with some help from Len Tower and others. Stallman wrote

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2688-722: The Linux kernel . With roughly 15 million lines of code in 2019, GCC is one of the largest free programs in existence. 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 . It was extended to compile C++ in December of that year. Front ends were later developed for Objective-C , Objective-C++ , Fortran , Ada , D , Go and Rust , among others. The OpenMP and OpenACC specifications are also supported in

2772-599: The (since 1995, object-oriented) programming language Ada . The Ada STONEMAN document formalized the program support environment (APSE) along with the kernel (KAPSE) and minimal (MAPSE). An Ada interpreter NYU/ED supported development and standardization efforts with the American National Standards Institute (ANSI) and the International Standards Organization (ISO). Initial Ada compiler development by

2856-583: The 13.1 release, GCC includes front ends for C ( gcc ), C++ ( g++ ), Objective-C and Objective-C++ , Fortran ( gfortran ), Ada ( GNAT ), Go ( gccgo ), D ( gdc , since 9.1), and Modula-2 ( gm2 , since 13.1) programming languages, with the OpenMP and OpenACC parallel language extensions being supported since GCC 5.1. Versions prior to GCC 7 also supported Java ( gcj ), allowing compilation of Java to native machine code. Regarding language version support for C++ and C, since GCC 11.1

2940-418: The C and C++ compilers. GCC has been ported to more platforms and instruction set architectures than any other compiler, and is widely deployed as a tool in the development of both free and proprietary software . GCC is also available for many embedded systems , including ARM -based and Power ISA -based chips. As well as being the official compiler of the GNU operating system , GCC has been adopted as

3024-587: The Early PL/I (EPL) compiler by Doug McIlory and Bob Morris from Bell Labs. EPL supported the project until a boot-strapping compiler for the full PL/I could be developed. Bell Labs left the Multics project in 1969, and developed a system programming language B based on BCPL concepts, written by Dennis Ritchie and Ken Thompson . Ritchie created a boot-strapping compiler for B and wrote Unics (Uniplexed Information and Computing Service) operating system for

3108-617: The FSF officially halted development on their GCC 2.x compiler, blessed EGCS as the official version of GCC, and appointed the EGCS project as the GCC maintainers in April 1999. With the release of GCC 2.95 in July 1999 the two projects were once again united. GCC has since been maintained by a varied group of programmers from around the world under the direction of a steering committee. GCC 3 (2002) removed

3192-440: The GCC steering committee decided to allow use of a C++ compiler to compile GCC. The compiler was intended to be written mostly in C plus a subset of features from C++. In particular, this was decided so that GCC's developers could use the destructors and generics features of C++. In August 2012, the GCC steering committee announced that GCC now uses C++ as its implementation language. This means that to build GCC from sources,

3276-433: The GCC versions developed for various Texas Instruments, Hewlett Packard, Sharp, and Casio programmable graphing calculators. GCC is licensed under the GNU General Public License version 3. The GCC runtime exception permits compilation of proprietary programs (in addition to free software) with GCC headers and runtime libraries. This does not impact the license terms of GCC source code. Compiler In computing ,

3360-528: The Sun 3/60 Solaris targeted to Motorola 68020 in an Army CECOM evaluation. There were soon many Ada compilers available that passed the Ada Validation tests. The Free Software Foundation GNU project developed the GNU Compiler Collection (GCC) which provides a core capability to support multiple languages and targets. The Ada version GNAT is one of the most widely used Ada compilers. GNAT is free but there

3444-670: The U.S. Military Services included the compilers in a complete integrated design environment along the lines of the STONEMAN document. Army and Navy worked on the Ada Language System (ALS) project targeted to DEC/VAX architecture while the Air Force started on the Ada Integrated Environment (AIE) targeted to IBM 370 series. While the projects did not provide the desired results, they did contribute to

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3528-471: The University of Cambridge was originally developed as a compiler writing tool. Several compilers have been implemented, Richards' book provides insights to the language and its compiler. BCPL was not only an influential systems programming language that is still used in research but also provided a basis for the design of B and C languages. BLISS (Basic Language for Implementation of System Software)

3612-476: The back end include the following: Christopher W. Fraser LCC is intended to be very simple to understand and is well-documented; its design is described in Fraser and Hanson's book A Retargetable C Compiler: Design and Implementation . The book includes most of the source code for version 3.6 of the compiler, which was written as a literate program using noweb . As of July 2011 the current version of LCC

3696-435: The basis of digital modern computing development during World War II. Primitive binary languages evolved because digital devices only understand ones and zeros and the circuit patterns in the underlying machine architecture. In the late 1940s, assembly languages were created to offer a more workable abstraction of the computer architectures. Limited memory capacity of early computers led to substantial technical challenges when

3780-433: The behavior of multiple functions simultaneously. Interprocedural analysis and optimizations are common in modern commercial compilers from HP , IBM , SGI , Intel , Microsoft , and Sun Microsystems . The free software GCC was criticized for a long time for lacking powerful interprocedural optimizations, but it is changing in this respect. Another open source compiler with full analysis and optimization infrastructure

3864-461: The code. These work on multiple representations, mostly the architecture-independent GIMPLE representation and the architecture-dependent RTL representation. Finally, machine code is produced using architecture-specific pattern matching originally based on an algorithm of Jack Davidson and Chris Fraser. GCC was written primarily in C except for parts of the Ada front end. The distribution includes

3948-480: The compiled language and the target architecture, starting from the GENERIC representation and expanding it to register transfer language (RTL). The GENERIC representation contains only the subset of the imperative programming constructs optimized by the middle end. In transforming the source code to GIMPLE, complex expressions are split into a three-address code using temporary variables . This representation

4032-422: The compiler is the "middle end." The exact set of GCC optimizations varies from release to release as it develops, but includes the standard algorithms, such as loop optimization , jump threading , common subexpression elimination , instruction scheduling , and so forth. The RTL optimizations are of less importance with the addition of global SSA-based optimizations on GIMPLE trees, as RTL optimizations have

4116-591: The compiler. By 1973 the design of C language was essentially complete and the Unix kernel for a PDP-11 was rewritten in C. Steve Johnson started development of Portable C Compiler (PCC) to support retargeting of C compilers to new machines. Object-oriented programming (OOP) offered some interesting possibilities for application development and maintenance. OOP concepts go further back but were part of LISP and Simula language science. Bell Labs became interested in OOP with

4200-571: The default target is gnu++17 , a superset of C++17 , and gnu11 , a superset of C11 , with strict standard support also available. GCC also provides experimental support for C++20 and C++23 . Third-party front ends exist for many languages, such as Pascal ( gpc ), Modula-3 , and VHDL ( GHDL ). A few experimental branches exist to support additional languages, such as the GCC UPC compiler for Unified Parallel C or Rust . GCC's external interface follows Unix conventions. Users invoke

4284-407: The development of C++ . C++ was first used in 1980 for systems programming. The initial design leveraged C language systems programming capabilities with Simula concepts. Object-oriented facilities were added in 1983. The Cfront program implemented a C++ front-end for C84 language compiler. In subsequent years several C++ compilers were developed as C++ popularity grew. In many application domains,

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4368-551: The development of compiler technology: Early operating systems and software were written in assembly language. In the 1960s and early 1970s, the use of high-level languages for system programming was still controversial due to resource limitations. However, several research and industry efforts began the shift toward high-level systems programming languages, for example, BCPL , BLISS , B , and C . BCPL (Basic Combined Programming Language) designed in 1966 by Martin Richards at

4452-424: The development of high-level languages followed naturally from the capabilities offered by digital computers. High-level languages are formal languages that are strictly defined by their syntax and semantics which form the high-level language architecture. Elements of these formal languages include: The sentences in a language may be defined by a set of rules called a grammar. Backus–Naur form (BNF) describes

4536-408: The different supported languages can be processed by the same back end . GCC started out using LALR parsers generated with Bison , but gradually switched to hand-written recursive-descent parsers for C++ in 2004, and for C and Objective-C in 2006. As of 2021 all front ends use hand-written recursive-descent parsers. Until GCC 4.0 the tree representation of the program was not fully independent of

4620-508: The difficulty in getting work accepted by the official GCC project was greatly frustrating for many, as the project favored stability over new features. The FSF kept such close control on what was added to the official version of GCC 2.x (developed since 1992) that GCC was used as one example of the "cathedral" development model in Eric S. Raymond 's essay The Cathedral and the Bazaar . In 1997,

4704-424: The early days, the approach taken to compiler design was directly affected by the complexity of the computer language to be processed, the experience of the person(s) designing it, and the resources available. Resource limitations led to the need to pass through the source code more than once. A compiler for a relatively simple language written by one person might be a single, monolithic piece of software. However, as

4788-491: The field of compiling began in the late 50s, its focus was limited to the translation of high-level language programs into machine code ... The compiler field is increasingly intertwined with other disciplines including computer architecture, programming languages, formal methods, software engineering, and computer security." The "Compiler Research: The Next 50 Years" article noted the importance of object-oriented languages and Java. Security and parallel computing were cited among

4872-464: The first (algorithmic) programming language for computers called Plankalkül ("Plan Calculus"). Zuse also envisioned a Planfertigungsgerät ("Plan assembly device") to automatically translate the mathematical formulation of a program into machine-readable punched film stock . While no actual implementation occurred until the 1970s, it presented concepts later seen in APL designed by Ken Iverson in

4956-423: The first compilers were designed. Therefore, the compilation process needed to be divided into several small programs. The front end programs produce the analysis products used by the back end programs to generate target code. As computer technology provided more resources, compiler designs could align better with the compilation process. It is usually more productive for a programmer to use a high-level language, so

5040-559: The first pass needs to gather information about declarations appearing after statements that they affect, with the actual translation happening during a subsequent pass. The disadvantage of compiling in a single pass is that it is not possible to perform many of the sophisticated optimizations needed to generate high quality code. It can be difficult to count exactly how many passes an optimizing compiler makes. For instance, different phases of optimization may analyse one expression many times but only analyse another expression once. Splitting

5124-933: The form of expressions without a change of language; and compiler-compilers , compilers that produce compilers (or parts of them), often in a generic and reusable way so as to be able to produce many differing compilers. A compiler is likely to perform some or all of the following operations, often called phases: preprocessing , lexical analysis , parsing , semantic analysis ( syntax-directed translation ), conversion of input programs to an intermediate representation , code optimization and machine specific code generation . Compilers generally implement these phases as modular components, promoting efficient design and correctness of transformations of source input to target output. Program faults caused by incorrect compiler behavior can be very difficult to track down and work around; therefore, compiler implementers invest significant effort to ensure compiler correctness . Compilers are not

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5208-454: The future research targets. A compiler implements a formal transformation from a high-level source program to a low-level target program. Compiler design can define an end-to-end solution or tackle a defined subset that interfaces with other compilation tools e.g. preprocessors, assemblers, linkers. Design requirements include rigorously defined interfaces both internally between compiler components and externally between supporting toolsets. In

5292-421: The idea of using a higher-level language quickly caught on. Because of the expanding functionality supported by newer programming languages and the increasing complexity of computer architectures, compilers became more complex. DARPA (Defense Advanced Research Projects Agency) sponsored a compiler project with Wulf's CMU research team in 1970. The Production Quality Compiler-Compiler PQCC design would produce

5376-434: The late 1950s. APL is a language for mathematical computations. Between 1949 and 1951, Heinz Rutishauser proposed Superplan , a high-level language and automatic translator. His ideas were later refined by Friedrich L. Bauer and Klaus Samelson . High-level language design during the formative years of digital computing provided useful programming tools for a variety of applications: Compiler technology evolved from

5460-408: The need for a strictly defined transformation of the high-level source program into a low-level target program for the digital computer. The compiler could be viewed as a front end to deal with the analysis of the source code and a back end to synthesize the analysis into the target code. Optimization between the front end and back end could produce more efficient target code. Some early milestones in

5544-570: The only language processor used to transform source programs. An interpreter is computer software that transforms and then executes the indicated operations. The translation process influences the design of computer languages, which leads to a preference of compilation or interpretation. In theory, a programming language can have both a compiler and an interpreter. In practice, programming languages tend to be associated with just one (a compiler or an interpreter). Theoretical computing concepts developed by scientists, mathematicians, and engineers formed

5628-667: The overall effort on Ada development. Other Ada compiler efforts got underway in Britain at the University of York and in Germany at the University of Karlsruhe. In the U. S., Verdix (later acquired by Rational) delivered the Verdix Ada Development System (VADS) to the Army. VADS provided a set of development tools including a compiler. Unix/VADS could be hosted on a variety of Unix platforms such as DEC Ultrix and

5712-511: The performance and the quality of the produced machine code. The middle end contains those optimizations that are independent of the CPU architecture being targeted. The main phases of the middle end include the following: Compiler analysis is the prerequisite for any compiler optimization, and they tightly work together. For example, dependence analysis is crucial for loop transformation . The scope of compiler analysis and optimizations vary greatly; their scope may range from operating within

5796-646: The phase structure of the PQC. The BLISS-11 compiler provided the initial structure. The phases included analyses (front end), intermediate translation to virtual machine (middle end), and translation to the target (back end). TCOL was developed for the PQCC research to handle language specific constructs in the intermediate representation. Variations of TCOL supported various languages. The PQCC project investigated techniques of automated compiler construction. The design concepts proved useful in optimizing compilers and compilers for

5880-417: The processor being targeted. The meaning of a tree was somewhat different for different language front ends, and front ends could provide their own tree codes. This was simplified with the introduction of GENERIC and GIMPLE, two new forms of language-independent trees that were introduced with the advent of GCC 4.0. GENERIC is more complex, based on the GCC 3.x Java front end's intermediate representation. GIMPLE

5964-429: The resource limitations of early systems, many early languages were specifically designed so that they could be compiled in a single pass (e.g., Pascal ). In some cases, the design of a language feature may require a compiler to perform more than one pass over the source. For instance, consider a declaration appearing on line 20 of the source which affects the translation of a statement appearing on line 10. In this case,

6048-445: The source code in that language and produces an abstract syntax tree ("tree" for short). These are, if necessary, converted to the middle end's input representation, called GENERIC form; the middle end then gradually transforms the program towards its final form. Compiler optimizations and static code analysis techniques (such as FORTIFY_SOURCE, a compiler directive that attempts to discover some buffer overflows ) are applied to

6132-490: The source code to build an internal representation of the program, called the intermediate representation (IR). It also manages the symbol table , a data structure mapping each symbol in the source code to associated information such as location, type and scope. While the frontend can be a single monolithic function or program, as in a scannerless parser , it was traditionally implemented and analyzed as several phases, which may execute sequentially or concurrently. This method

6216-469: The source language grows in complexity the design may be split into a number of interdependent phases. Separate phases provide design improvements that focus development on the functions in the compilation process. Classifying compilers by number of passes has its background in the hardware resource limitations of computers. Compiling involves performing much work and early computers did not have enough memory to contain one program that did all of this work. As

6300-515: The standard compiler by many other modern Unix-like computer operating systems , including most Linux distributions. Most BSD family operating systems also switched to GCC shortly after its release, although since then, FreeBSD and Apple macOS have moved to the Clang compiler, largely due to licensing reasons. GCC can also compile code for Windows , Android , iOS , Solaris , HP-UX , AIX and DOS . In late 1983, in an effort to bootstrap

6384-806: The standard libraries for Ada and C++ whose code is mostly written in those languages. On some platforms, the distribution also includes a low-level runtime library, libgcc , written in a combination of machine-independent C and processor-specific machine code , designed primarily to handle arithmetic operations that the target processor cannot perform directly. GCC uses many additional tools in its build, many of which are installed by default by many Unix and Linux distributions (but which, normally, aren't present in Windows installations), including Perl , Flex , Bison , and other common tools. In addition, it currently requires three additional libraries to be present in order to build: GMP , MPC , and MPFR . In May 2010,

6468-463: The standard release have included: Additional processors have been supported by GCC versions maintained separately from the FSF version: The GCJ Java compiler can target either a native machine language architecture or the Java virtual machine 's Java bytecode . When retargeting GCC to a new platform, bootstrapping is often used. Motorola 68000, Zilog Z80, and other processors are also targeted in

6552-440: The syntax of "sentences" of a language. It was developed by John Backus and used for the syntax of Algol 60 . The ideas derive from the context-free grammar concepts by linguist Noam Chomsky . "BNF and its extensions have become standard tools for describing the syntax of programming notations. In many cases, parts of compilers are generated automatically from a BNF description." Between 1942 and 1945, Konrad Zuse designed

6636-421: The time when Sun Microsystems was unbundling its development tools from its operating system , selling them separately at a higher combined price than the previous bundle, which led many of Sun's users to buy or download GCC instead of the vendor's tools. While Stallman considered GNU Emacs as his main project, by 1990 GCC supported thirteen computer architectures, was outperforming several vendor compilers, and

6720-432: Was developed for a Digital Equipment Corporation (DEC) PDP-10 computer by W. A. Wulf's Carnegie Mellon University (CMU) research team. The CMU team went on to develop BLISS-11 compiler one year later in 1970. Multics (Multiplexed Information and Computing Service), a time-sharing operating system project, involved MIT , Bell Labs , General Electric (later Honeywell ) and was led by Fernando Corbató from MIT. Multics

6804-560: Was inspired by the SIMPLE representation proposed in the McCAT compiler by Laurie J. Hendren for simplifying the analysis and optimization of imperative programs . Optimization can occur during any phase of compilation; however, the bulk of optimizations are performed after the syntax and semantic analysis of the front end and before the code generation of the back end; thus a common, though somewhat self-contradictory, name for this part of

6888-524: Was listed as the author but cited others for their contributions, including Tower for "parts of the parser, RTL generator, RTL definitions, and of the Vax machine description", Jack Davidson and Christopher W. Fraser for the idea of using RTL as an intermediate language, and Paul Rubin for writing most of the preprocessor. Described as the "first free software hit" by Peter H. Salus , the GNU compiler arrived just at

6972-450: Was used commercially by several companies. As GCC was licensed under the GPL, programmers wanting to work in other directions—particularly those writing interfaces for languages other than C—were free to develop their own fork of the compiler, provided they meet the GPL's terms, including its requirements to distribute source code . Multiple forks proved inefficient and unwieldy, however, and

7056-470: Was written in the PL/I language developed by IBM and IBM User Group. IBM's goal was to satisfy business, scientific, and systems programming requirements. There were other languages that could have been considered but PL/I offered the most complete solution even though it had not been implemented. For the first few years of the Multics project, a subset of the language could be compiled to assembly language with

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