The Model of Compilation

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The Model of Compilation

• Natawut Nupairoj, Ph.D.
• Department of Computer Engineering
• Chulalongkorn University

2
Outline

• Overview.
• Front-End
• Lexical Analysis.
• Syntactic Analysis.
• Semantic Analysis.
• Back-End
• Code Generation.
• Code Optimization.

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Overview

• Translate a source program (in language S) into
  an equivalent object program (in language O).

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The Model of Compilation
Analysis (Front-End)
Synthesis (Back-End)
IntermediateRepresentation
source
object

• Reduce Complexity
• Source/Target Independent
• Plug-able Compiler
• IR contain sufficient information
• tree-like structure the syntax tree or
• Assembly-like format three-address code.

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Front-End

• Lexical Analysis
• group the input stream into tokens
• Syntactic Analysis
• see if the source is valid or correct
• Contextual/Semantic Analysis
• make sure the program is meaningful or
  semantically correct.

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Front-End Components
Group token.
Scanner
Source program (text stream)
identifier main
symbol (
m
a
i
n
(
)

token
Construct parse tree.
next-token
Symbol Table
Parser
parse-tree
Check semantic/contextual.
Intermediate Representation (file or in memory)
Semantic Analyzer
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Lexical Analysis

• Scanner.
• Group the input stream into tokens
• identifiers.
• numbers.
• keywords.
• symbols signs.
• Lexeme Character sequence forming a token.
• Eliminate all blanks and comments.

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Example Tokens
position initial rate 60
1. identifier position 2. assignment symbol 3.
identifier initial 4. plus symbol
5. identifier rate 6. muliplication symbol 7.
integer-literal 60
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Syntax Analysis

• Parser.
• Check if the source is grammatically correct.
• Construct a parse tree.

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Mini-Triangle Syntax

• single-Command V-name Expression
• Identifier ( Expression )
• if Expression then single-Command
• else single-Command
• while Expression do single-Command
• let Declaration in single-Command
• begin Command end

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Mini-Triangle Syntax

• Expression primary-Expression
• Expression Operator primary-Expression
• primary-Expression Integer-Literal
• V-name
• Operator primary-Expression
• ( Expression )
• V-name Identifier
• ...
• Operator - / lt gt \

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Example Parse Tree
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Semantic Analysis

• Make sure that the program is meaningful.
• Walk the parse tree to check
• Type checking.
• Type conversion.
• Example
• rate 60
• rate is a real variable
• rate inttoreal(60)
• Generate IR (can also done by parser).

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Example of IRAbstract Syntax Tree (AST)

• position initial rate 60

position initial rate 60
interior node operation children
arguments leaves identifiers or constants
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Example of IRThree-Address Code
position initial rate 60

• tmp rate 60
• tmp initial tmp
• position tmp

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Back-End

• Code Optimization
• improve IR machine-independent.
• improve object code machine-depedent.
• optimizing compiler.
• widely-used.
• Code Generation
• generate object code.
• assign memory/register locations.
• instruction selection.

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Front-End Components
Machine-independent optimization.
IR Optimizer
Intermediate Representation (file or in memory)
IR
Generate object code.
Symbol Table
Code Generator
Machine-dependent optimization
Object code
Peephole Optimizer
Object code (assembly or binary)
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Other Phases

• Symbol-Table Management
• information about identifier being-used.
• name
• type
• scope
• Scanner creates an entry into the table.
• Error Handler
• what to do when found errors in the source.

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Compiler-Construction Tools

• Parser generators.
• Generate a parser from a CFG.
• Yacc, Bison.
• Scanner generators.
• Generate a scanner from regular expressions.
• Lex, Flex.