Structure
GCC's external interface is generally standard for a UNIX compiler. Users invoke a driver program named gcc, which interprets command arguments, decides which language compilers to use for each input file, runs the assembler on their output, and then possibly runs the linker to produce a complete executable binary.
Each of the language compilers is a separate program that inputs source code and outputs machine code. All have a common internal structure. A per-language front end parses 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 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 is written primarily in C except for parts of the Ada front end. The distribution includes the standard libraries for Ada, C++, and Java 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.
In May 2010, the GCC steering committee decided to allow use of a C++ compiler to compile GCC. The compiler will be written 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, a C++ compiler is required that understands C++ 2003. For more details on the rationale and specific changes, please refer to the C++ conversion page.
Read more about this topic: GNU Compiler Collection
Famous quotes containing the word structure:
“Who says that fictions only and false hair
Become a verse? Is there in truth no beauty?
Is all good structure in a winding stair?
May no lines pass, except they do their duty
Not to a true, but painted chair?”
—George Herbert (1593–1633)
“There is no such thing as a language, not if a language is anything like what many philosophers and linguists have supposed. There is therefore no such thing to be learned, mastered, or born with. We must give up the idea of a clearly defined shared structure which language-users acquire and then apply to cases.”
—Donald Davidson (b. 1917)
“The verbal poetical texture of Shakespeare is the greatest the world has known, and is immensely superior to the structure of his plays as plays. With Shakespeare it is the metaphor that is the thing, not the play.”
—Vladimir Nabokov (1899–1977)