Phases and Passes

The most obvious overall task of a compiler is to read a program in one language — the ‘source’ program in the ‘source’ language — and to translate it to produce an equivalent program in another language — the ‘object’ program in the ‘object’ language. The object language is usually the machine language of a computer, or something close to it, and the source program is usually in a ‘high-level’ language such as FORTRAN, PASCAL, ALGOL 68, SIMULA 67 or BCPL, because translation from high-level language to machine language is the practical problem which compilers exist to solve. Compilers can be written to translate from any kind of programming language into any other, however, with varying degrees of efficiency of the resulting object program.