Compiler Design Lectures

7/30/2019 Compiler Design Lectures

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CS 434

Compilers Design

Dr. Ayman Hamarsheh


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Lecture 1

Introduction

Programs, Interpreters and Translators


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Programming languages are notations for

describing computations to people and tomachines

All the software running on all thecomputers 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


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a compiler is a program that can read aprogram in one language - the source

language - and translate it into anequivalent program in another language -the targetlanguage;

An important role of the compiler is toreport any errors in the source programthat it detects during the translationprocess.

If the target program is an executablemachine-language program, it can then becalled by the user to process inputs andproduce outputs


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An interpreteris another common kind oflanguage processor.

Instead of producing a target program as atranslation, an interpreter appears to directlyexecute the operations specified in the sourceprogram on inputs supplied by the user.

The machine-language target program producedby a compiler is usually much faster than aninterpreter at mapping inputs to outputs .

An interpreter, however, can usually give better

error diagnostics than a compiler, because itexecutes the source program statement bystatement.


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The main advantages of compilers

They produce programs which run

quickly.

They can spot syntax errors while theprogram is being compiled (i.e. you

are informed of any grammatical

errors before you try to run the

program).


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The main advantages of interpreters

There is no lengthy "compile time", i.e. you

do not have to wait between writing a

program and running it, for it to compile They tend to be more "portable", which

means that they will run on a greater

variety of machines.


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In addition to a compiler, several other

programs may be required to create anexecutable target program.

A source program may be divided intomodules stored in separate files.

The task of collecting the source programis sometimes entrusted to a separateprogram, called a preprocessor.

The preprocessor may also expandshorthands, called macros, into sourcelanguage statements.


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The compiler may produce an assembly

language program as its output, becauseassembly language is easier to produce as

output and is easier to debug.

The assembly language is then processedby a program called an assemblerthat

produces relocatable machine code as its

output.


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Large programs are often compiled in pieces, so

the relocatable machine code may have to be

linked together with other relocatable object files

and library files into the code that actually runs

on the machine.

The linkerresolves external memory addresses,where the code in one file may refer to a location

in another file.

The loaderthen puts together all of the

executable object files into memory for

execution.


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Source Program Translators TargetProgram

Compilers

Interpreters


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Lecture 2

The Structure of a Compiler

Analysis-Synthesis Model of

Translation (Compilation)


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There are two parts of compilation: Analysis part

Synthesis part

Front

End

Back

End

Intermediate

Representation

Source

code

Machine

Errors

code


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The Analysis Part:

It is often called the front end of the compiler

Breaks up the source program into constituent

pieces and imposes a grammatical structure on

these pieces.

Creates an intermediate representation of thesource program.

If the analysis part detects that the source

program is either syntactically ill formed or

semantically unsound, then it must provide

informative messages, so the user can take

corrective action.


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Collects information about the source

program and stores it in a data structurecalled a symbol table, which is passed

along with the intermediate representation

to the synthesis part. During analysis, the operations implied by

the source program are determined and

recorded in a hierarchical structure calleda tree.


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The Synthesis Part:

It is often called the back end of the

compiler

constructs the desired target program from

the intermediate representation and the

information in the symbol table.


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Phases of compilation process:

Compiler operates as a sequence of phases,each of which transforms one representation of

the source program to another.

In practice, several phases may be grouped

together, and the intermediate representationsbetween the grouped phases need not be

constructed explicitly.

Symbol table, which stores information about the

entire source program, is used by all phases of

the compiler.


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Phases of compilation process:

Lexical Analysis Syntax Analysis

Semantic Analysis

Intermediate Code Generation

Machine-Independent code optimization

Code Generation

Machine-Dependent Code Optimization


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Issues in compiler design The compiler deals with many big-picture issues

Compiler construction brings togethertechniques from disparate parts of ComputerScience.

Compilers are engineered objectssoftwaresystems built with distinct goals in mind.

In building a compiler, the compiler writer makesmyriad design decisions, each decision has animpact on the resulting compiler.

a well designed compiler must observe isinviolable.


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Lecture 3

Programming Language

Specifications


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Definition of Syntax

In computer science, the syntax of aprogramming language is the set of rules thatdefine the combinations of symbols that areconsidered to be correctly structured programsin that language.

The syntax of a language defines its surfaceform.

Text-based programming languages are basedon sequences of characters.

visual programming languages are based on thespatial layout and connections between symbols(which may be textual or graphical).


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Definition of Syntax

The syntaxof a programming languagedescribes the proper form of its programs.

The syntax of textual programming

languages is usually defined using acombination of regular expressions (forlexical structure) and Backus-Naur Form(for grammatical structure) to inductivelyspecify syntactic categories (nonterminals)and terminalsymbols.


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The syntax of a language describes theform of a valid program, but does not

provide any information about the meaning

of the program or the results of executingthat program.

syntax of most programming languages

can be specified using a Type-2 grammar,i.e., they are context-free grammars.


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Semantics and Pragmatics

The two stages of analysis semantics andpragmatics, are concerned with getting at themeaningof a sentence.

In the first stage (semantics) a partialrepresentation of the meaning is obtained basedon the possible syntactic structure(s) of thesentence, and on the meanings of the words inthat sentence

In the second stage, the meaning is elaboratedbased on contextualand world knowledge


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Semantics

In general, the input to the semantic stage

of analysis may be viewed as being a set

of possible parsesof the sentence, and

information about the possible wordmeanings.


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Lecture 4

In-depth Study of SyntacticSpecifications


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Syntactic

The syntactic analysis of source codeusually entails the transformation of the

linear sequence of tokens into a

hierarchical syntax tree (abstract syntax

trees are one convenient form of syntax

tree)


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Syntax definition

The syntax of textual programming

languages is usually defined using a

combination of regular expressions (for

lexical structure) and Backus-Naur Form(for grammatical structure) to inductively

specify syntactic categories (nonterminals)

and terminalsymbols


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Syntax definition

The syntax of a language describes theform of a valid program, but does notprovide any information about the meaning

of the program or the results of executingthat program.

The meaning given to a combination ofsymbols is handled by semantics

Not all syntactically correct programs aresemantically correct


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Using natural language as an example, it

may not be possible to assign a meaningto a grammatically correct sentence or the

sentence may be false:

"John is a married bachelor. " isgrammatically well-formed but has no

generally accepted meaning.


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No ambiguity allowed in programming

languages in form (syntax) and meaning(semantics)

Distinction between syntax and semantics:

many programming languages havefeatures that meanthe same (shared

semantics) but are expresseddifferently

identifying which is which helps thelearning curve


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Syntax Specification

Formalism: set of production rules Microsyntax rules: concatenation, alternation

(choice among finite alternatives), Kleene

closure

- The set of strings produced by these three rules

is a regular setorregular language

- The rules are specified by regular expressions

they generate the regular language- Strings in the regular language are recognized

by scanners

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