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Languages and Compilers (SProg og Oversættere). Structure of the compiler. Structure of the compiler. Describe the phases of the compiler and give an overall description of what the purpose of each phase is and how the phases interface. The “Phases” of a Compiler. Source Program. - PowerPoint PPT Presentation
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Languages and Compilers(SProg og Oversættere)
Structure of the compiler
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Structure of the compiler
• Describe the phases of the compiler and give an overall description of what the purpose of each phase is and how the phases interface
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The “Phases” of a Compiler
Syntax Analysis
Contextual Analysis
Code Generation
Source Program
Abstract Syntax Tree
Decorated Abstract Syntax Tree
Object Code
Error Reports
Error Reports
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Single Pass Compiler
Compiler Driver
Syntactic Analyzer
calls
calls
Contextual Analyzer Code Generator
calls
Dependency diagram of a typical Single Pass Compiler:
A single pass compiler makes a single pass over the source text, parsing, analyzing and generating code all at once.
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Multi Pass Compiler
Compiler Driver
Syntactic Analyzer
callscalls
Contextual Analyzer Code Generator
calls
Dependency diagram of a typical Multi Pass Compiler:
A multi pass compiler makes several passes over the program. The output of a preceding phase is stored in a data structure and used by subsequent phases.
input
Source Text
output
AST
input output
Decorated AST
input output
Object Code
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1) Syntax Analysis -> AST
Program
LetCommand
SequentialDeclaration
n Integer c Char c ‘&’ n n + 1
Ident Ident Ident Ident Ident Ident Ident OpChar.Lit Int.Lit
SimpleT
VarDecl
SimpleT
VarDecl
SimpleV
Char.Expr
SimpleV
VNameExp Int.Expr
AssignCommand BinaryExpr
SequentialCommand
AssignCommand
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2) Contextual Analysis -> Decorated AST
Contextual Analysis
Decorated Abstract Syntax Tree
Error Reports
Abstract Syntax Tree
Contextual analysis:
• Scope checking: verify that all applied occurrences of identifiers are declared
• Type checking: verify that all operations in the program are used according to their type rules.
Annotate AST:• Applied identifier occurrences => declaration• Expressions => Type
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2) Contextual Analysis -> Decorated AST
Program
LetCommand
SequentialDeclaration
n
Ident Ident Ident Ident
SimpleT
VarDecl
SimpleT
VarDecl
Integer c Char c ‘&’ n n + 1
Ident Ident Ident OpChar.Lit Int.Lit
SimpleV
Char.Expr
SimpleV
VNameExp Int.Expr
AssignCommand BinaryExpr
SequentialCommand
AssignCommand
:char
:char
:int
:int
:int :int
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Contextual Analysis
Finds scope and type errors.
AssignCommand
:char
Example 1:
:int
***TYPE ERROR (incompatible types in assigncommand)
Example 2:
foo
Ident
SimpleV
foo not found
***SCOPE ERROR: undeclared variable foo
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3) Code Generation
• Assumes that program has been thoroughly checked and is well formed (scope & type rules)
• Takes into account semantics of the source language as well as the target language.
• Transforms source program into target code.
Code Generation
Decorated Abstract Syntax Tree
Object Code
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3) Code Generation
let var n: integer; var c: charin begin c := ‘&’; n := n+1end
PUSH 2LOADL 38STORE 1[SB]LOAD 0LOADL 1CALL addSTORE 0[SB]POP 2HALT
n
Ident Ident
SimpleT
VarDecl
Integer
address = 0[SB]
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A somewhat more complex compiler
