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CHAPTER 1

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COMPILER

A compileris a program that reads a programwritten in one language the source language

and translates it into an equivalent program in

another language the target language

COMPILERSOURCE

PROGRAM

ERROR

MESSAGES

TARGET

PROGRAM

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A VERY Brief Compiler History

1950s first generation of compilers; much of theearly work on compiling dealt with the translation

of arithmetic formulas into machine code.

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PARTS OF COMPILATION

There are two parts to compilation:1. Analysis breaks up the source program into

constituent pieces and creates an intermediate

representation of the source program

2. Synthesis constructs the desired targetprogram from the intermediate representation

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SOFTWARE TOOLS THAT MANIPULATE

SOURCE PROGRAMS

1. Structure Editors takes as input a sequence ofcommands to build a source program

2. Pretty Printers Analyzes a program and prints it in

such a way that the structure of the program

becomes clearly visible.3. Static Checker a static checker reads a program,

analyzes it, and attempts to discover potential bugs

without running the program.

4. Interpreters instead of producing a target programas a translation, an interpreter performs the

operations implied by the source program.

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PREPROCESSOR

Several programs may be required to create anexecutable target program. A source program

may be divided into modules stored in separate

files.

The task of collecting the source program is

entrusted to the PREPROCESSOR.

The preprocessor may also expand shorthands or

macros into source language statements

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ANALYSIS OF THE SOURCE

PROGRAM

THREE PHASES OF ANALYSIS1. Linear Analysis the stream of characters making

up the source program is read from left-to-right

and grouped into tokens

2. Hierarchical Analysis characters or tokens aregrouped hierarchically into nested collections with

collective meaning

3. Semantic Analysis certain checks are performed

to ensure that the components of a program fittogether meaningfully

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Lexical Analysis In a compiler, linear analysis is called lexicalanalysisorscanning.

For example, in lexical analysis the characters in theassignment statement

position := initial + rate * 60

would be grouped into the following tokens:1. The identifierposition2. The assignment symbol :=3. The identifierinitial4. The plus sign

5. The identifierrate6. The multiplication sign7. The number60

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Syntax Analysis

Hierarchical Analysis is called parsingorsyntaxanalysis. It involves grouping the tokens of thesource of the program into grammatical phrases

that are used by the compiler to synthesize

output.

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Parse Tree

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Semantic Analysis

The semantic analysis phase checks the sourceprogram for semantic errors and gathers type

information for the subsequent code generation

phase.

It uses the hierarchical structure determined by

the syntax analysis phase to identify the

operators and operands of expressions and

statements

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Phases of a Compiler

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Symbol Table Management

An essential function of a compiler is to recordthe identifiers used in the source program and

collect various attributes of each identifier

The attributes may provide information about the

storage allocated for the identifier

Type

Scope

Number and type of arguments

Type returned

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Symbol Table

A symbol table is a data structure containing arecord for each identifier with fields for the

attributes of the identifier

When an identifier in the source program is

detected by the lexical analyzer, the identifier is

entered into the symbol table.

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Error Detection and Reporting

Each phase can encounter errors. However, afterdetecting an error, a phase must somehow deal

with that error, so that compilation may proceed,

allowing further errors in the source program to

be detected.

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The Analysis Phases

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Intermediate Code Generation

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Code Optimization and Code

Generator