Compiler Design and Construction - Old Questions

3. What is the role of intermediate code generation in the entire compilation process? Convert the following into three address code.

        a+(b-c)*d

Intermediate code is used to translate the source code into the machine code. Intermediate code lies between the high-level language and the machine language. The given program in a source language is converted into an equivalent program in an intermediate language by the intermediate code generator. Intermediate codes are machine independent codes. 

Roles of Intermediate code are :

• It acts as a glue between front-end and backend (or source and machine codes).
  
• If the compiler directly translates source code into the machine code without generating intermediate code then a full native compiler is required for each new machine.
• The intermediate code keeps the analysis portion same for all the compilers that's why it doesn't need a full compiler for every unique machine.
• Intermediate code generator receives input from its predecessor phase and semantic analyzer phase. It takes input in the form of an annotated syntax tree.
• Using the intermediate code, the second phase of the compiler synthesis phase is changed according to the target machine.
• Intermediate code generator lowers abstraction from source level.
• Complete some syntactic checks, perform more semantic checks. For e.g. break should be inside loop or switch only.
  

The intermediate code representation are

• Graphical representation e.g. Abstract Syntax Tree(AST) , DAGS
• Postfix notations
• Three Address codes

Given expression:

a+(b-c)*d

Converting it into three address code:

    t₁ = b-c

    t₂ = t₁*d

    t₃ = a+t₂

For given expression the quadruples is:

For given expression, the triples is: