A
compiler translates the code written in one language to some other language
without changing the meaning of the program. It is also expected that a
compiler should make the target code efficient and optimized in terms of time
and space.
A
compiler acts as a translator, transforming human-oriented programming
languages into computer-oriented
machine languages.
Programming
Machine
Language
Compiler
Language
(Source)
(Target)
Any compiler
must perform two major tasks
Compiler
·
Analysis of the source program
·
Synthesis of a machine-language
program
Compiler
Phases:
The
compilation process is a sequence of various phases. 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. Let us understand the
phases of a compiler.
Lexical
analysis:
Lexical
analysis is the first phase of a compiler. It takes the modified source
code from language pre-processors that are written in the form of sentences.
The lexical analyzer breaks these syntaxes into a series of tokens,
by removing any whitespace or comments in the source code.
A
programming language must include the specification of syntax (structure) and
semantics (meaning).
Syntax
typically means the context-free syntax because of the almost universal use of
context-free-grammar (CFGs)
Ex.
a =
b + c is syntactically legal
b +
c = a is illegal
Token:
The token name
is an abstract symbol representing a kind of lexical unit, e.g., a particular
keyword, or sequence of input characters denoting an identifier.
Syntax
Analysis:
The
next phase is called the syntax analysis or parsing. It takes the token
produced by lexical analysis as input and generates a parse tree (or syntax
tree). In this phase, token arrangements are checked against the source code
grammar, i.e. the parser checks if the expression made by the tokens is
syntactically correct.
Semantic Analysis:
Semantic
analysis checks whether the parse tree constructed follows the rules of
language. For example, assignment of values is between compatible data types,
and adding string to an integer.
Intermediate
Code Generation:
Interpreters
are easier to write and can provide better error messages (symbol table is
still available) Interpreters are at least 5 times slower than machine code
generated by compilers Interpreters also require much more memory than machine
code generated by compilers Examples: Perl, Python, Unix Shell, Java, BASIC,
LISP
Code
Optimization:
The
next phase does code optimization of the intermediate code.
Code
Generation:
In
this phase, the code generator takes the optimized representation of the
intermediate code and maps it to the target machine language.
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