A compiler is a program that translates one programming language into another. It has six main phases: lexical analysis, syntax analysis, semantic analysis, intermediate code generation, code optimization, and code generation. It also uses a symbol table to store identifiers and their properties and handles errors detected in each phase.

2. What is compiler?
 Compiler is a program which takes one language as input and translate
it into an equivalent another language.
 Compiler is divided into two parts: Analysis and Synthesis
 Basic model of compiler can be represented as follows:

3.  Conceptually, a compiler operates into phases, each of which
transform the source program from one representation to another.
 Each phase takes input from its previous stage, has its own representation of
source program, and feeds its output to the next phase of the compiler.
 The compiler has six phases called as lexical analyzer, syntax analyzer,
semantic analyzer, intermediate code generator, code optimizer and
code generator.
 Two other activities, symbol-table management and error handling,
are interacting with the six phases of compiler.
Phases of compiler

4. Phases of compiler

5.  To support the phases of compiler, symbol table is maintained. The
task of symbol table is to store identifiers used in program.
 Basically symbol table is a data structure used to store the
information about identifiers.
 The symbol table allows us to find the record for each identifier
quickly and to store or retrieve data from that record efficiently.
 While doing the semantic analysis and intermediate code
generation, we need to know what type of identifiers are.
 During code generation typically information about how much
storage is allocated to identifier is seen.
Symbol-table management

6. Error detection and reporting
 In compilation, each phase detects error. These errors must be reported
to error handler whose task is to handle the error so that the compilation
can proceed.
 Normally, the errors are reported in the form of message.
 Large number of error can be detected in syntax analysis phase. Such
error are known as syntax error.
 During semantic analysis, type mismatch kind of error is usually
detected.

7. Lexical analysis
 The lexical analysis is also known as scanning.
 It is the phase of compilation in which the complete source code is
scanned and source program is broken up into group of strings called
token.
 A token is sequence of character having a collective meaning.
 E.g. Total = count + rate
 After lexical analysis, the statement is broken up into series of tokens as
follows:
identifier total, assignment operator, identifier count, plus sign, identifier
rate

8. syntax analysis
 The syntax analysis is also known as parsing.
 In this phase token generated by lexical analysis are grouped together
to form a hierarchical structure known as syntax tree.

9. semantic analysis
 Once syntax is checked in the syntax analyzer phase the next phase i.e.
semantic analyzer determines the meaning of the source string.
 For example meaning of source string means matching parenthesis,
matching if…else statement, performing arithmetic operation of
expression that are type compatible or checking operation scope.

10. Intermediate code generation
 The intermediate code is a kind of code which is easy to generate and
this code can be easily converted to target code.
 This code is in variety of form such as three address code, quadruple,
triple, posix.
 For example, total = count + rate * 10
 Intermediate code using three address code method is
t1 := int_to_float(10)
t2 := rate * t1
t3 := count + t2
total := t3

11. Code optimization
 The code optimization phase attempt to improve the intermediate
code
 This is necessary to have a faster executing code or less consumption of
memory
 Thus, by optimizing the code the overall running time of the target
program can be improved.

12. Code generation
 In this phase, target code is generated.
 The intermediate code instructions are translated into sequence of
machine instruction
 For example, total = count + rate * 10
 Target code will be
MOV rate, R1
MUL #10.0, R1
MOV count, R2
ADD R2, R1
MOV R1, total