The Analysis-Synthesis Model

• The ANALYSIS part (Figure 2)
  • breaks up the source program into constituent pieces (words, phrases)
  • and creates an intermediate representation of the source program.
  Informally, the compiler must understand the structure and meaning of the source program.

  Figure 2: From a source line to an intermediate representation via an expression tree. In this example it is assumed that the variables x and y are known to be of type real which explains the conversion of 10 from int to real.

  
• The INTERMEDIATE REPRESENTATION (IR) is an abstract machine language
  • that can express the target-machine operations,
  • without committing too much machine-specific detail.
• The IR should be easy
  • to produce (from the source program) and
  • to translate (to the target language).
• In our example (Figure 2) the IR is a THREE-ADDRESS CODE:
  • each instruction has at most 3 operands,
  • each instruction has at most 1 operator in addition to the assignment.

  Figure 3: The interest of an intermediate representation.

  
  On the right picture of Figure 3 the arrows going from programming languages to IR are called COMPILER FRONT ENDS and those going from IR to computer architectures are called COMPILER BACK ENDS.
• The SYNTHESIS part (Figure 4)
  • performs code optimization,
  • and constructs the desired target program from the intermediate representation.

  Figure 4: From an intermediate representation to a sequence of target instructions.