Page "Code generation (compiler)" Paragraph 10

In a compiler that uses an intermediate language, there may be two instruction selection stages — one to convert the parse tree into intermediate code, and a second phase much later to convert the intermediate code into instructions from the instruction set of the target machine.

This second phase does not require a tree traversal ; it can be done linearly, and typically involves a simple replacement of intermediate-language operations with their corresponding opcodes.

However, if the compiler is actually a language translator ( for example, one that converts Eiffel to C ), then the second code-generation phase may involve building a tree from the linear intermediate code.