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A

PRESENTATION ON

Chapter 1 2301373: Introduction 1

BASICS OF COMPILER DESIGN

SUBMITTED BY:-HARSHIT KHANNA0115CS081040

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What is a Compiler?

Acompiler is a computer program

that translates a program in a

source language into an equivalent

program in a target language.

Asource program/code is a

program/code written in thesource language, which is usually a

high-level language.

Atarget program/code is a

program/code written in the target

language, which often is a machinelanguage or an intermediate code.


compilerSourceprogram Targetprogram

Error

message

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Process ofCompiling


scanner

parser

Semantic analyzer

Intermediate code generator

Code optimization

Code generator

Code optimization

Stream of characters

Stream of tokens

Parse/syntax tree

Annotated tree

Intermediate code

Intermediate code

Target code

Target code

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Some Data Structures

Symbol table

Literal table

Parse tree


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Symbol Table

Identifiers are names ofvariables, constants,functions, data types, etc.

Store information associated with identifiers

Information associated with different types ofidentifiers can be different

Information associated with variables are name, type,

address,size (for array), etc.

Information associated with functions are name,type ofreturn value, parameters, address, etc.


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Symbol Table (contd)

Accessed in every phase ofcompilers

The scanner, parser, and semantic analyzer put

names ofidentifiers in symbol table.

The semantic analyzer stores more information

(e.g. data types) in the table.

The intermediate code generator, code optimizer

and code generator use information in symboltable togenerate appropriate code.

Mostly use hash table for efficiency.


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Literal table

Store constants and strings used in program

reduce the memory size by reusing constants and

strings

Can be combined with symbol table


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Parse tree

Dynamically-allocated, pointer-based

structure

Inf

ormation

for di

ffere

nt data types related

to parse treesneed to be stored somewhere.

Nodes are variant records, storing information

for differenttypes ofdata

Nodesstore pointersto informationstored in

other data structure, e.g. symbol table


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Scanning

A scanner reads a streamofcharacters and

puts them together into some meaningful

(with respect to the source language) units

calledtokens.

It produces a streamoftokens for the next

phase ofcompiler.


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Parsing

Aparser gets a streamoftokens from thescanner, anddetermines ifthe syntax(structure) ofthe program is correct according

to the (context-free) grammar ofthe sourcelanguage.

Then, it produces a data structure, called aparse tree or an abstract syntax tree, whichdescribes the syntactic structure oftheprogram.


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Semantic analysis

It gets the parse tree from the parser together withinformation about some syntactic elements

It determines ifthe semantics or meaningofthe programis correct.

This part deals with static semantic. semantic ofprograms that can be checkedby readingofffrom

the programonly.

syntax of the language which cannot be described in context-free grammar.

Mostly, a semantic analyzer does type checking. It modifies the parse tree in order toget that (static)

semantically correct code.


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Intermediate code generation

An intermediate code generator

takes a parse tree from the semantic analyzer

generates a program in the intermediate language.

In some compilers, a source program is translated

into an intermediate code first and then the

intermediate code is translated into the target

language. In other compilers, a source program is translated

directly into the target language.


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Intermediate code generation (contd)

Using intermediate code is beneficial whencompilers which translates a single sourcelanguage tomany target languages are required.

The front-endofa compiler scanner to intermediatecode generator can be usedfor every compilers.

Different back-ends code optimizer and codegenerator is requiredfor each target language.

One ofthe popular intermediate code is three-address code. A three-address code instruction isin the formof x= y op z.


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Code optimization

Replacing an inefficient sequence ofinstructions

with a better sequence ofinstructions.

Sometimes called code improvement.

Code optimization can be done:

after semantic analyzing performedon a parse tree

after intermediate code generation performedon a intermediate code

after code generation performedon a target code


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Code generation

A code generator

takes either an intermediate code or a parse tree

produces a target program.


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Error Handling

Error can be found in every phase ofcompilation.

Errors foundduring compilation are calledstatic (or

compile-time)errors.

Errors foundduring execution are calleddynamic (or

run-time)errors

Compilers need todetect, report, and recover

from error found in source programs Error handlers are different in different phases of

compiler.


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HISTORYOFINTRODUCTIONOF

PARSINGTECHNIQUES

Recursive-descent parsing was introduced.

Nuar designedAlgol60, Pascals ancestor, whichallows recursive call.

Backus-Nuar form (BNF) was used todescribedAlgol60.

LL(1) parsing was proposedby Lewis andStearns.

General LRparsing was inventedby Knuth.

SLRparsing was developedby DeRemer.


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History (1970s)

LALR was develpoedby DeRemer.

Aho andUllman founded the theory ofLR

parsing techniques. Yacc (Yet Another Compiler Compiler) was

developedby Johnson.

Type inference was studiedby Milner.


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TH

ANKY

OU


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