Compiler lec 2

Compilers Design
Course
Ramadan Babers
Compilers Design – Lec2
Faculty of Science Helwan University
1st Term – 2017/2018

Phases of Compiler
2
Lexical Analyzer (Scanner)
reads a stream of characters and puts them
together into some meaningful (with respect to
the source language) units called tokens.
Lexical Analyzer
(Scanner)Character
Stream
Token
Stream
CD-Course-FSH 1st Term 2017-2018

Phases of Compiler
3
Lexical Analyzer (Continue)
 Token
 Token (terminal, attribute)
 Symbol Table (reserved words)
Lexical Analyzer
(Scanner)Character
Stream
Token Stream
(terminal, attribute)

Phases of Compiler
4
Syntax Analyzer (Parsing)
• Takes a stream of tokens from the scanner,
and
• Determines if the syntax (structure) of the
program is correct according to the
(context-free) grammar of the source
language.
Syntax Analyzer
Token Syntax Tree

Phases of Compiler
5
Syntax Analyzer (Parsing) continue
• It generates a data structure, called a
parse tree or an abstract syntax tree,
which describes the syntactic structure of
the program.

Phases of Compiler
6
Syntax Analyzer (Parsing) continue
Ex:
 Statement:
id=id op id
 Statement:
id=id [num]
 Statement:
if (id op num) { } / if(xy==20) { }

Phases of Compiler
7
Semantic Analyzer
 Statement:
id op id op id
x = y + z (semantically correct)
But if
Int = float + fn (semantically incorrect)

Phases of Compiler
8
Intermediate Code Generator
Intermediate CodeSource Code Machine Code
Intermediate Code
C
Intel
Pascal
Basic
Mac

Phases of Compiler
9
Code Optimizer
Code optimizing means
 Faster,
 Shorter,
 Target code consumes less power.

Phases of Compiler
10
Example:
position := initial + rate * 60
would be grouped into the following tokens;
1. The identifier position
2. The assignment symbol :=
3. The identifier initial
4. The plus sign
5. The identifier rate.
6. The multiplication sign.
7. The number 60
LexicalAnalyzer
Syntax Analyzer

Phases of Compiler
11
Example:
<id, position> <=> <id, initial> <+> <id, rate> <*> <num, 60>
<id, 1> <=> <id, 2> <+> <id, 3> <*> <num, 60>
Lexical Analyzer
1 Position ----
2 Initial ----
3 rate ----

Phases of Compiler
12
Example:
Syntax Analyzer
=
<id,1> +
<id,2>
<id,3>
*
60

Phases of Compiler
13
Example:
Semantic Analyzer
=
<id,1> +
<id,2>
<id,3>
*
int to float

Phases of Compiler
14
Example:
Intermediate Code
t1= int to float (60)
t2= id3 * t1
t3= id2 + t2
id1=t3

Phases of Compiler
15
Example:
Code Optimizer
t1= int to float (60)
t2= id3 * t1
t3= id2 + t2
id1=t3
t1= id3 * 60.0
id1= id2 + t1

Phases of Compiler
16
Example:
LDF R2 , id3
MULF R2 , R2 , #60.0
LDF R1 , id2
ADDF R1 , R1 , R2
STF id1 , R1
Code Generator
LDF: Load float
MULF: Multi float
ADDF: Add float
STF: Store float

17
Chapter 2
A Simple Syntax-Directed
Translator

Introduction
18
Syntax Tree
Generate
Parsing
Group of production
Terminal
Grammar
Nonterminal

Introduction
19
Syntax
Parser Grammar
Token

Introduction
20
Example:
Code required for the process: 5+6+7
exp exp + exp
exp 0
1
2
---
9
exp num + exp
num 0
1
2
---
9
exp exp + num
exp num
num 0
1
2
---
9

Introduction
21
Example:
Code required for the process: A=B=C=-----=Z
exp L = exp
exp L
L A
B
C
---
Z
exp exp = L
exp L
L A
B
C
---
Z

Compiler lec 2

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