Explain with a neat diagram phases of a compiler by taking an example A=B+C*60.

 1) Lexical Analyzer

— The first phase of compiler is lexical analyzer it reads stream of characters in the source program

— Groups the characters into meaningful sequences – lexemes

— For each lexeme, a token is produced as output

—  <token-name , attribute-value>

Token-name : symbol used during syntax analysis

Attribute-value : an entry in the symbol table for this token

— Information from symbol table is needed for syntax analysis and code generation

— Consider the following assignment statement 

2) Syntax Analysis

The second phase of compiler is  syntax analysis  is also  called Parsing

— Parser uses the tokens to create a tree-like intermediate representation

— Depicts the grammatical structure of the token stream

— Syntax tree is one such representation

                                 Interior node – operation

                                 Children  - arguments of the operation

Other phases use this syntax tree to help analyze source program and generate target program

3) Semantic Analysis

The third phase of compiler is Semantic Analyzer

— Checks semantic consistency with language using:

                               Syntax tree  and Information in symbol table

— Gathers type information and save in syntax tree or symbol table

— Type Checks each operator for matching operands

                               Ex: Report error if floating point number is used as index of an array

— Coercions or type conversions

                         Binary arithmetic operator applied to a pair of integers or floating point numbers

                           If applied to floating point and integer, compiler may convert integer to floating-

                            point number

4) Intermediate Code Generation

     After syntax and semantic analysis  Intermediate Code Generation is the fourth  phase of compiler

— Compilers generate machine-like intermediate representation

— This intermediate representation should have the two properties:

                         Should be easy to produce

                         Should be easy to translate into target machine

             Three-address code

— Sequence of assembly-like instructions with three operands per instruction

— Each operand acts like a register

                        Points to be noted about three-address instructions are:

— Each assignment instruction has at most one operator on the right side

— Compiler must generate a temporary name to hold the value computed by a three-address instruction

— Some instructions have fewer than three operands

5) Code Optimization

            Attempt to improve the target code

— Faster code, shorter code or target code that consumes less power

                        Optimizer can deduce that

— Conversion of 60 from int to float can be done once  at compile time

— So, the inttofloat can be eliminated by replacing 60 with 60.0

— t3 is used only once to transmit its value to id1

6) Code Generation

— Takes intermediate representation as input

— Maps it into target language

— If target language is machine code

                        Registers or memory locations are selected for each of the variables used

                        Intermediate instructions are translated into sequences of machine instructions

                        performing the same task

— Assignment of registers to hold variables is a crucial aspect