Compiler-Intermediate Code Generation & Code Optimization

  • Three Address Code
  • Control Sequence
  • Variable Declaration

Intermediate Code

Intermediate code separates the front end and the back end.
It is an intermediate level between

  • a high level parse tree and
  • low level microprocessor instructions.

It is internal to compilers. Different compilers may have different intermediate codes.

Possible types of intermediate code:

  • Syntax trees
  • Static single assignment
  • Three address code

Three Address Code

Each 3AC instruction consists of at most

  • one operator (binary or unary) and three address (variable number)

For example,

  • (binary operator)
  • (unary operator)
  • (copy/ assignment)
  • (unconditional , is the label of the destination)
  • (conditional goto)

To convert a parse tree to 3AC, we need two synthesized attributes for each node in the parse tree.

Suppose we have a grammar production

  • stores the name of the variable containing the value of .
  • stores the sequence of 3AC that computes the value if .

The function is used when the temporary variable names for intermediate results are generated.

Example

Define the attributes for the following grammar

  • "||" means "followed by"
  • No because is an assignment, not computing a value.

  • (intrinsic)
  • (nothing to compute)

Control Sequence

Variable Declaration

Loop

If Statement

Table Of Contents
Compiler-Intermediate Code Generation & Code Optimization
Intermediate Code
Three Address Code
Example
Control Sequence
Variable Declaration
Loop
If Statement