Another advantage of the three-phase design (which follows directly from retargetability) is that the compiler serves a broader set of programmers than it would if it only supported one source language and one target. For an open source project, this means that there is a larger community of potential contributors to draw from, which naturally leads to more enhancements and improvements to the compiler. This is the reason why open source compilers that serve many communities (like GCC) tend to generate better optimized machine code than narrower compilers like FreePASCAL. This isn't the case for proprietary compilers, whose quality is directly related to the project's budget. For example, the Intel ICC Compiler is widely known for the quality of code it generates, even though it serves a narrow audience. A final major win of the three-phase design is that the skills required to implement a front end are different than those required for the optimizer and back end. Separating these makes it easier for a "front-end person" to enhance and maintain their part of the compiler. While this is a social issue, not a technical one, it matters a lot in practice, particularly for open source projects that want to reduce the barrier to contributing as much as possible.

The most popular design for a traditional static compiler (like most C compilers) is the three phase design whose major components are the front end, the optimizer and the back end (Figure 11.1). The front end parses source code, checking it for errors, and builds a language-specific Abstract Syntax Tree (AST) to represent the input code. The AST is optionally converted to a new representation for optimization, and the optimizer and back end are run on the code.