The document discusses the fundamentals of compilers, detailing the phases of compilation that transform source code into target machine code, including lexical analysis, syntax analysis, semantic analysis, and code optimization. It explains the roles of various components such as scanners, parsers, and semantic routines in processing code and generating intermediate representations. Additionally, it highlights the significance of optimizations like peephole and loop optimizations in enhancing the efficiency of the generated machine code.

1. Introduction to Compilers
Mr. Sameer Prembabu Mamadapure
Information Technology Department
International Institute of Information Technology, I²IT
www.isquareit.edu.in

2. Compilers
 “Compilation”
 Translation of a program written in a source language
into a semantically equivalent program written in a
target language
Compiler
Error messages
Source
Program
Target
Program
Input
Output

3. Lexical Analyzer
Syntax Analyzer
Semantic Analyzer
Intermediate Code Generator
Machine-Independent
Code Optimizer
Code Generator
Machine-Dependent
Code Optimizer
character stream
token stream
syntax tree
syntax tree
target-machine code
Symbol
Table
Phases of a Compiler
Error Handler
intermediate representation
target-machine code
intermediate representation

4. Lexical Analyzer
Syntax Analyzer
Semantic Analyzer
character stream
position = initial + rate * 60
<id,1> <=> <id,2> <+> <id,3> <*> <60>
=
<id,1>
<id,2>
<id,3>
+
*
60
=
<id,1>
<id,2>
<id,3>
+
*
inttofloat
60
Example:-

5. Intermediate Code Generator
Machine-Independent
Code Optimizer
Code Generator
t1 = inttofloat(60)
t2 = id3 * t1
t3 = id2 + t2
id1 = t3
t1 = id3 * 60.0
id1 = id2 + t1
L R2, id3
MULF R2, #60.0
L R1, id2
ADDF R1, R2
ST id1, R1
1 position …
2 initial …
3 rate …
SYMBOL TABLE

6. The Phases of a Compiler
Phase Output Sample
Programmer (source code producer) Source string A=B+C;
Scanner (performs lexical analysis) Token string ‘A’, ‘=’, ‘B’, ‘+’, ‘C’, ‘;’
And symbol table with names
Parser (performs syntax analysis
based on the grammar of the
programming language)
Parse tree or abstract syntax tree ;
|
=
/
A +
/
B C
Semantic analyzer (type checking,
etc)
Annotated parse tree or abstract
syntax tree
Intermediate code generator Three-address code, quads, or RTL int2fp B t1
+ t1 C t2
:= t2 A
Optimizer Three-address code, quads, or RTL int2fp B t1
+ t1 #2.3 A
Code generator Assembly code MOVF #2.3,r1
ADDF2 r1,r2
MOVF r2,A
Peephole optimizer Assembly code ADDF2 #2.3,r2
MOVF r2,A

7. 7
 Any compiler must perform two major tasks
 Analysis of the source program
 Synthesis of a machine-language program
The Structure of a Compiler (1)
Compiler
Analysis Synthesis

8. The Structure of a Compiler
8
Scanner Parser
Semantic
Routines
Code
Generator
Optimizer
Source
Program Tokens Syntactic
Structure
Symbol and
Attribute
Tables
(Used by all Phases of The Compiler)
(Character Stream)
Intermediate
Representation
Target machine code

9. 9
Scanner Parser
Semantic
Routines
Code
Generator
Optimizer
Source
Program Tokens Syntactic
Structure
Symbol and
Attribute
Tables
(Used by all
Phases of
The Compiler)
Scanner
 The scanner begins the analysis of the source program
by reading the input, character by character, and
grouping characters into individual words and symbols
(tokens)
 RE ( Regular expression )
 NFA ( Non-deterministic Finite Automata )
 DFA ( Deterministic Finite Automata )
 LEX
(Character Stream)
Intermediate
Representation
Target machine code

10. 10
Scanner Parser
Semantic
Routines
Code
Generator
Optimizer
Source
Program Tokens Syntactic
Structure
Symbol and
Attribute
Tables
(Used by all
Phases of
The Compiler)
Parser
 Given a formal syntax specification (typically as a context-
free grammar [CFG] ), the parse reads tokens and groups
them into units as specified by the productions of the
CFG being used.
 As syntactic structure is recognized, the parser either calls
corresponding semantic routines directly or builds a
syntax tree.
 CFG ( Context-Free Grammar )
 BNF ( Backus-Naur Form )
 GAA ( Grammar Analysis Algorithms )
 LL, LR, SLR, LALR Parsers
 YACC
(Character Stream)
Intermediate
Representation
Target machine code

11. 11
Scanner Parser
Semantic
Routines
Code
Generator
Optimizer
Source
Program
(Character Stream)
Tokens Syntactic
Structure
Intermediate
Representation
Symbol and
Attribute
Tables
(Used by all
Phases of
The Compiler)
Semantic Routines
 Perform two functions
 Check the static semantics of each construct
 Do the actual translation
 The heart of a compiler
 Syntax Directed Translation
 Semantic Processing Techniques
 IR (Intermediate Representation)
Target machine code

12. 12
Scanner Parser
Semantic
Routines
Code
Generator
Optimizer
Source
Program Tokens Syntactic
Structure
Symbol and
Attribute
Tables
(Used by all
Phases of
The Compiler)
Optimizer
 The IR code generated by the semantic routines is
analyzed and transformed into functionally equivalent but
improved IR code
 This phase can be very complex and slow
 Peephole optimization
 loop optimization, register allocation, code scheduling
 Register and Temporary Management
 Peephole Optimization
(Character Stream)
Intermediate
Representation
Target machine code

13. 13
Source
Program
(Character Stream)
Scanner
Tokens
Parser
Syntactic
Structure
Semantic
Routines
Intermediate
Representation
Optimizer
Code
Generator
Code Generator
 Interpretive Code Generation
 Generating Code from Tree/Dag
 Grammar-Based Code Generator
Target machine code

14. 14
Scanner
[Lexical Analyzer]
Parser
[Syntax Analyzer]
Semantic Process
[Semantic analyzer]
Code Generator
[Intermediate Code Generator]
Code Optimizer
Tokens
Parse tree
Abstract Syntax Tree w/ Attributes
Non-optimized Intermediate
Code
Optimized Intermediate Code
Code Optimizer
Target machine code

15. Thank You
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