COMPILER CONSTRUCTION

Instructor:
Mr. Sheraz Babar

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Lecture 02

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Language Processing System
Language Processing System
 Preprocessor
A preprocessor produce input to compilers. They may
perform the following functions.
1. Macro processing: A preprocessor may allow a user
to define macros that are short hands for longer
constructs.
2. File inclusion: A preprocessor may include header
files into the program text.
3. Rational preprocessor: these preprocessors
augment older languages with more modern flow-ofcontrol
and data structuring facilities.
4. Language Extensions: These preprocessor attempts
to add capabilities to the language by certain amounts to
build-in macro 4
Language Processing System
 COMPILER
Compiler is a translator program that translates a program
written in (HLL) the source program and translate it into an
equivalent program in (MLL) the target program. As an
important part of a compiler is error showing to the
programmer.

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Language Processing System
 INTERPRETER
An interpreter is a program that appears to
execute a source program as if it were machine
language.

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Language Processing System
 ASSEMBLER
Programmers found it difficult to write or read programs in
machine language. They begin to use a mnemonic
(symbols) for each machine instruction, which they would
subsequently translate into machine language. Such a
mnemonic machine language is now called an assembly
language. Programs known as assembler were written to
automate the translation of assembly language in to
machine language. The input to an assembler program is
called source program, the output is a machine language
translation (object program).

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Language Processing System
 Linker
Linker is a computer program that links and merges various
object files together in order to make an executable file. All
these files might have been compiled by separate assemblers.
The major task of a linker is to search and locate referenced
module/routines in a program and to determine the memory
location where these codes will be loaded, making the program
instruction to have absolute references.

 Loader
Loader is a part of operating system and is responsible for
loading executable files into memory and execute them. It
calculates the size of a program instructionsanddata and
creates memory space for it. It initializes various registers to
initiate execution. 8
LIST OF COMPILERS
1. Ada compilers
2 .ALGOL compilers
3 .BASIC compilers
4 .C# compilers
5 .C compilers
6 .C++ compilers
7 .COBOL compilers
8 .Common Lisp compilers
9. ECMAScript interpreters
10. Fortran compilers
11 .Java compilers
12. Pascal compilers
13. PL/I compilers
14. Python compilers
15. Smalltalk compilers
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Compiler Architecture
A compiler can broadly be divided into two phases based
on the way they compile.
 Analysis Phase
Known as the front-end of the compiler, the analysis
phase of the compiler reads the source
program, divides it into core parts and then checks for
lexical, grammar and syntax errors.The
analysis phase generates an intermediate representation
of the source program and symbol table,
which should be fed to the Synthesis phase as input.

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Compiler Architecture
 Synthesis Phase
Known as the back-end of the compiler, the synthesis phase
generates the target program with
the help of intermediate source code representation and symbol table.
A compiler can have many phases and passes.

Pass : A pass refers to the traversal of a compiler through

the entire program.

Phase : A phase of a compiler is a distinguishable stage, which

takes input from the previous stage, processes and yields output
that can be used as input for the next stage. A pass can have
more than one phase.

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Phases of a compiler

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Phases of a compiler
 Lexical Analysis:-
LA or Scanners reads the source program one
character at a time, carving the source program into a
sequence of automic units called tokens.

 Syntax Analysis:-
The second stage of translation is called Syntax
analysis or parsing. In this phase expressions,
statements, declarations etc… are identified by using
the results of lexical analysis. Syntax analysis is
aided by using techniques based on formal grammar
of the programming language.
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Phases of a compiler
 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.

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Phases of a compiler
 Intermediate Code Generations:-
An intermediate representation of the final
machine language code is produced. This phase
bridges the analysis and synthesis phases of
translation.

 Code Optimization :-
This is optional phase described to improve the
intermediate code so that the output runs faster
and takes less space.

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Phases of a compiler

 Code Generation:-
The last phase of translation is code generation. A
number of optimizations to reduce the length of
machine language program are carried out during
this phase. The output of the code generator is
the machine language program of the specified
computer.

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 The Phases of a Compiler
Phase Output Sample

Programmer (source code producer) Source string A=B+C;

Scanner (performs lexical analysis) Token string ‘A’, ‘=’, ‘B’, ‘+’, ‘C’, ‘;’
And symbol table with names

Parser (performs syntax analysis based on the Parse tree or abstract syntax tree ;
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grammar of the programming language) =
/ \
A +
/ \
B C

Semantic analyzer (type checking, etc) Annotated parse tree or abstract syntax
tree

Intermediate code generator Three-address code, quads, or int2fp B t1

RTL(Register Transfer Language) + t1 C t2
:= t2 A

Optimizer Three-address code, quads, or RTL int2fp B t1

+ t1 #2.3 A

Code generator Assembly code MOVF #2.3,r1

ADDF2 r1,r2
MOVF r2,A
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The Grouping of Phases
 Compiler front and back ends:
• Front end: analysis (machine independent)
• Back end: synthesis (machine dependent)
 Compiler passes:
 Pass is the reading of a source file once.
• A collection of phases is done only once (single pass) or multiple times
(multi pass)
• Single pass: usually requires everything to be defined before being used in source
program
• Multi pass: compiler may have to keep entire program representation in memory

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Compiler-Construction Tools
 Software development tools are available to
implement one or more compiler phases
• Scanner generators
• Parser generators
• Syntax-directed translation engines
• Automatic code generators
• Data-flow engines

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The End

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