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1. Compiler Construction
(Introduction)
Lecture-1
By
Shahid Akbar
MS (Computer Science)

2. Goals Of This Course
Know how to build a compiler for a (simplified) (programming)
language
Know how to use compiler construction tools, such as generators for
scanners (Lexical Analyzer) and parsers(Semantic Analyzer )
Be able to write LL(1), LR(1), and LALR(1) grammars (for new
languages)
Be familiar with compiler analysis and optimization techniques
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3. Grading Policy
 Mid Term 20
 Final Term 60
 Quizzes / Assignments 20
Total 100
Note= 75% Attendance is compulsory for Exams
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4. Textbook
Compilers: Principles, Techniques, and Tools, 2/E.
Alfred V. Aho, Columbia University
Monica S. Lam, Stanford University
Ravi Sethi, Avaya Labs
Jeffrey D. Ullman, Stanford University
Dragon

5. What is Compiler?
 The world as we know it depends on programming languages,
C, C++, Java, Web programming, and etc.
 All the software running on all the computers was written in some programming
language.
 Before a program can be run, it first must be translated into a form in which it
can be executed by a computer.
The software systems that do this translation are called compilers.

6. Different compilers
 VC, VC++ (visual compiler, Microsoft products)
 GCC
Dev C compiler , where Dev C is Integrated development environment (IDE)
 JavaC
Java compiler
 FORTRAN
 Pascal
 Visual Basic (internet programming)

7. Why Compilation?
The conversion of high level language into low level object code and
machine code.
High level language can be understandable by the human , contain
English words and phrases, but computer can only understand
machine language (Low level language), that’s we need compilation
for interaction between human and computer.

8. Computer Languages-1
 Machine language (Low Level Language)
 Only language computer directly understands
 Defined by hardware design
 Machine-dependent
 Generally consist of strings of numbers
 Ultimately 0s and 1s
 Instruct computers to perform elementary operations
 One at a time
 Cumbersome for humans
 Example:
+1300042774
+1400593419
+1200274027
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9. Computer Languages-2
 Assembly language
 English-like abbreviations representing elementary
computer operations
 Clearer to humans
 Incomprehensible to computers
 Translator programs (assemblers)
 Convert to machine language
 Example:
LOAD BASEPAY
ADD OVERPAY
STORE GROSSPAY
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10. Computer Languages-3
 High-level languages
 Similar to everyday English, use common mathematical
notations
 Single statements accomplish substantial tasks
 Assembly language requires many instructions to
accomplish simple tasks
 Translator programs (compilers)
 Convert to machine language
 Interpreter programs
 Directly execute high-level language programs
 Example:
grossPay = basePay + overTimePay
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11. A compiler is program that covert high level language to
Assembly languages , similarly an Assembler is a program that
convert the Assembly language to Machine Level language
Compiler Vs Assembler

12. Assembler VS Compiler
It is used to translate the program written in assembly language
into Machine language.
An assembler perform the translation process in the similar way
as compiler, but Assembler is a translator program for low
level programming language , while a compiler is the translator
program for high level languages

13. Compilers and Interpreters
“Compilation”
Translation of a program written in a source language into a
semantically equivalent program written in a target language.
An important role of the compiler is to report any errors in the
source program , errors are detected during the translation
process.
Compiler
Error messages
Source
Program
(HLL)
Target
Program
Input
Output
Execution
Compilation (Error Checking
(A L L)

14. Compilers and Interpreters (cont’d)
Interpreter
Source
Program
Input (Execution)
Output
Error messages
“Interpretation”
 Language processor
Performing the operations implied in the source program on
input supplied by users.

15. Complier Vs Interpreter
 In interpreter both execution and compilation process are combined ,At first a
statement is compiled and then executed.
 In compiler , A program is compiled one time and it can be execute again and
again until you need.
 While in interpreter A program/statement will be compiled and executed again
and again (depend on number of execution)
 e.g: if you need to execute a program 100 times, it requires 100 time compilation
and 100 times execution in interpreter
 Note : 1) Compiler is fast than interpreter (Why)
2) Error diagnosis of interpreter is better than compiler

16. Interpreter Compiler
Translates program statement by statement at a
time.
Scans the entire program and translates it as a
whole into machine code
It takes less amount of time to analyze the
source code but the overall execution time is
slower.(Time consuming)
It takes large amount of time to analyze the
source code but the overall execution time is
comparatively faster.
Continues translating the program until the first
error is met, in which case it stops. Hence
debugging is easy.
It generates the error message only after
scanning the whole program. Hence debugging
is comparatively hard.
Programming language like Python, Ruby use
interpreters.
Programming language like C, C++ use
compilers.

17. Compiler History
1952: First compiler (linker/loader) written by Grace Hopper for A-0
programming language
1957: First complete compiler for FORTRAN by John Backus and team
1960: COBOL compilers for multiple architectures
1962: First self-hosting compiler for LISP

18. Compiler Construction requirements
Programming languages (parameter passing, variable scoping,
memory allocation, etc)
theory (automata, context-free languages, etc)
Algorithms and data structures (hash tables, graph algorithms,
dynamic programming, etc)
Computer architecture (assembly programming)
Software Engineering.

19. Compiler Qualities
Make the Code Accurate
Compiler runs fast
Compile time proportional to program size
Support for separate compilation
Efficient to check syntax errors
Works well with the debugger
Good diagnostics for flow anomalies
Cross language calls --- interface compatibilities
Consistent, predictable optimization

20. A General language processing System
Preprocessor
HLL
Pure HLL
Compiler
Assembler
Linker/Loader
Assembly Language
Relocatable machine Code
Target Machine Code
#include < ?? . h >
# define Const variable
File Inclusion
Macro Expansion
NO preprocessor Directives
MOV a, R1
ADD #2, R1
MOV R1, b
i.e. b:= a +2
0001 01 00 00000000
0011 01 10 00000010
0010 01 00 00000100
Loading the data(relocatable
machine Code) and instruction to the
proper locations

21. Phases of Compiler
Lexical Analyzer
Syntax Analyzer
Semantic Analyzer
Intermediate Code
Generator
Code Optimizer
Target Code Generator
Character Stream (H L L)
Token Stream
Syntax Tree
Syntax Tree
(semantically verified
meaningful)
3 Address Code
Assembly code
Symbol Table
Reduce size of program
(number of lines)
Error Handler

23. Phase Output Sample
Programmer Source string A=B+C;
Scanner (performs lexical
analysis)
Token string ‘A’, ‘=’, ‘B’, ‘+’, ‘C’, ‘;’
And symbol table for identifiers
Parser (performs syntax analysis
based on the grammar of the
programming language)
Parse tree or abstract syntax tree ;
|
=
/
A +
/
B C
Semantic analyzer (type
checking, etc)
Parse tree or abstract syntax tree
Intermediate code generator Three-address code int2fp B t1
+ t1 C t2
:= t2 A
Optimizer Three-address code int2fp B t1
+ t1 #2.3 A
Code generator Assembly code MOVF #2.3,r1
ADDF2 r1,r2
MOVF r2,A
Peephole optimizer Assembly code ADDF2 #2.3,r2
MOVF r2,A