Phases Of Compiler In System Programming!!!!

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Phases Of Compiler In System Programming !!! 

Phases of compiler :


  1. Lexical analysis
  2. Syntax analysis
  3. Semantic analysis
  4. Intermediate code generation
  5. Code optimization
  6. Code generation

Phases Of Compiler In System Programming!!!!
Phases Of Compiler In System Programming!!!!


Lexical Analysis 


Lexical analysis is the first phase of compiler which is also termed as scanning.

Source program is scanned to read the stream of characters and those characters are grouped to form a sequence called lexemes which produces token as output.

Token: Token is a sequence of characters that represent lexical unit, which matches with the pattern, such as keywords, operators, identifiers etc.

Lexeme: Lexeme is instance of a token i.e., group of characters forming a token. ,

Pattern: Pattern describes the rule that the lexemes of a token takes. It is the structure that must be matched by strings.

Once a token is generated the corresponding entry is made in the symbol table.

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Input: stream of characters

Output: Token

Token Template: <token-name, attribute-value>

Example:  c=a+b*e;
c : operand
= : operator
a : operand
+ : operator
b : operand
* : operator
e : operand

                                   

Syntax Analysis



Syntax analysis is the second phase of compiler which is also called as parsing.

Parser converts the tokens produced by lexical analyzer into a tree like representation called parse tree.

A parse tree describes the syntactic structure of the input.

Syntax tree is a compressed representation of the parse tree in which the operators appear as interior nodes and the operands of the operator are the children of the node for that operator.

Input: Tokens

Output: Syntax tree
           

Semantic Analysis


Semantic analysis is the third phase of compiler.

It checks for the semantic consistency.

Type information is gathered and stored in symbol table or in syntax tree.

Performs type checking.

         

Intermediate Code Generation


Intermediate code generation produces intermediate representations for the source program which are of the following forms:


  •      Postfix notation
  •      Three address code
  •      Syntax tree


Most commonly used form is the three address code.

It should be easy to produce.

It should be easy to translate into target program.

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Code Optimization


Code optimization phase gets the intermediate code as input and produces optimized intermediate code as output.

It results in faster running machine code.

It can be done by reducing the number of lines of code for a program.

This phase reduces the redundant code and attempts to improve the intermediate code so that faster-running machine code will result.

During the code optimization, the result of the program is not affect.

To improve the code generation, the optimization involves


  •        Deduction and removal of dead code (unreachable code).
  •        Calculation of constants in expressions and terms.
  •        Collapsing of repeated expression into temporary string.
  •        Loop unrolling.
  •        Moving code outside the loop.
  •        Removal of unwanted temporar


Code Generation


Code generation is the final phase of a compiler.

It gets input from code optimization phase and produces the target code or object code as result.

Intermediate instructions are translate into a sequence of machine instructions that perform the same task.

The code generation involves


  •      Allocation of register and memory.
  •      Generation of correct references.
  •      Generation of correct data types.
  •       Generate the missing code.


                LDF R2, id3

                MULF R2, # 5.0

                LDF R1, id2

                ADDF R1, R2

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