Introduction to compiler development

INTRODUCTION
TO COMPILER
DEVELOPMENT
Compiler Construction
PRESENTED BY
PRESENTED BY
PRESENTED BY
D E E P
C S - E 1 9 - 0 1 5

WHAT IS COMPILER
A compiler is a special program that processes statements written in a
particular programming language and turns them into machine language or
"code" that a computer's processor uses. Typically, a programmer writes
language statements in a language such as C++ or C one line at a time using
an editor. The file that is created contains what are called the source
statements. The programmer then runs the appropriate language compiler,
specifying the name of the file that contains the source statements.

Towards the end of the 1950s, machine-independent programming
languages were first proposed. Subsequently, several experimental
compilers were developed. The first compiler was written by Grace
Hopper, in 1952, for the A-0 programming language. The FORTRAN team
led by John Backus at IBM is generally credited as having introduced the
first complete compiler in 1957. COBOL was an early language to be
compiled on multiple architectures, in 1960
HISTORY OF COMPILER

WHY DO WE NEED A
COMPILER?
A Computer understands only binary language and executes instructions
coded in binary language. It cannot execute a single instruction given in any
other form. Therefore, we must provide instructions to the computer in binary
language. Means we must write computer programs entirely in binary
language (sequence of 0s and 1s). So, there was a need of a translator that
translates the computer instructions given in English language to binary
language.

Computers do not understand human languages. In fact, at the lowest
level, computers only understand sequences of numbers that represent
operational codes (op codes for short). On the other hand, it would be very
difficult for humans to write programs in terms of op codes. Therefore,
programming languages were invented to make it easier for humans to
write computer programs.
Programming languages are for humans to read and understand. The
program (source code) must be translated into machine language so that
the computer can execute the program (as the computer only
understands machine language). The way that this translation occurs
depends on whether the programming language is a compiled language
or an interpreted language.
HOW COMPILER WORKS

WORK OF 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.
HOW COMPILER WORK
THROUGH ITS PHASES

LEXICAL ANALYSIS

The first phase of scanner works as a text scanner. This phase scans the
source code as a stream of characters and converts it into meaningful
lexemes. Lexical analyzer represents these lexemes in the form of tokens
as:
<token-name, attribute-value>

#include <iostream>
int main() {
cout << "Hello World!";
return 0;
}
HELLO WORLD PROGRAM

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. Also, the semantic analyzer keeps track of
identifiers, their types and expressions; whether
identifiers are declared before use or not etc. The
semantic analyzer produces an annotated syntax
tree as an output.

After semantic analysis, the compiler generates an
intermediate code of the source code for the target machine.
It represents a program for some abstract machine. It is in
between the high-level language and the machine language.
This intermediate code should be generated in such a way
that it makes it easier to be translated into the target machine
code.
INTERMEDIATE CODE GENERATION

CODE OPTIMIZATION

THE NEXT PHASE DOES CODE OPTIMIZATION OF THE
INTERMEDIATE CODE. OPTIMIZATION CAN BE ASSUMED
AS SOMETHING THAT REMOVES UNNECESSARY CODE
LINES, AND ARRANGES THE SEQUENCE OF STATEMENTS
IN ORDER TO SPEED UP THE PROGRAM EXECUTION
WITHOUT WASTING RESOURCES (CPU, MEMORY).

CODE GENERATION

IN THIS PHASE, THE CODE GENERATOR TAKES THE
OPTIMIZED REPRESENTATION OF THE INTERMEDIATE
CODE AND MAPS IT TO THE TARGET MACHINE
LANGUAGE. THE CODE GENERATOR TRANSLATES THE
INTERMEDIATE CODE INTO A SEQUENCE OF (GENERALLY)
RE-LOCATABLE MACHINE CODE. SEQUENCE OF
INSTRUCTIONS OF MACHINE CODE PERFORMS THE TASK
AS THE INTERMEDIATE CODE WOULD DO.

SYMBOL TABLE

IT IS A DATA-STRUCTURE MAINTAINED THROUGHOUT ALL
THE PHASES OF A COMPILER. ALL THE IDENTIFIER'S
NAMES ALONG WITH THEIR TYPES ARE STORED HERE.
THE SYMBOL TABLE MAKES IT EASIER FOR THE
COMPILER TO QUICKLY SEARCH THE IDENTIFIER RECORD
AND RETRIEVE IT. THE SYMBOL TABLE IS ALSO USED
FOR SCOPE MANAGEMENT.

Introduction to compiler development

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