Lecture # 4
Chapter 1 (Left over Topics)
Chapter 3 (continue)
Left over Topics of Chapter 1
• What is Analysis /Synthesis Model of Compilation?
• Symbol Table Management
• Error Detection and Reporting
• What is meant by grouping of compilation phases into
Front End and Back End?
• What is meant by Single / Multiple Passes?
• What are the Compiler Construction Tools available?
The Analysis-Synthesis Model of
Compilation
• There are two parts to compilation:
– Analysis determines the operations implied by the
source program which are recorded in a tree
structure
– Synthesis takes the tree structure and translates
the operations therein into the target program
3
Another way..
• Analysis: breaks the source program into constituent
pieces and creates intermediate representation
• Synthesis: constructs target program from the
intermediate representation
• The first three phases namely: Lexical Analysis, Syntax
Analysis and Semantic Analysis form the analysis part
• The last three phases form the Synthesis part
Symbol Table Management
• An essential function of a compiler is to record
the identifiers used in the source program and
to collect information about various attributes
of each identifier
• A symbol table is a data structure containing
an entry for each identifier with fields for the
attributes of the identifier
Error Detection and Reporting
• Each phase of the compiler can encounter error.
• After detecting error the compiler must deal with that
error so that compilation can proceed.
• A lexical analyzer will detect errors where characters
do not form a token
• Errors where token violates the syntax are determined
by syntax analysis
• If the compiler tries to add two variables one of which
is the name of a function and another is an array then
Symantic Analysis will throw error
Section 1.5: The Grouping of Phases
• Compiler phases are grouped into front and back ends:
– Front end: analysis (machine independent)
– Back end: synthesis (machine dependent)
• Front End focuses on understanding the source program and
the backend focuses on mapping programs to the target
machine.
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Compiler Passes
• Compiler Passes:
– A collection of phases is done only once (single pass) or
multiple times (multi pass)
• Single pass: usually requires everything to be defined
before being used in source program
• Multi pass: compiler may have to keep entire program
representation in memory
Section 1.6: Compiler-Construction
Tools
• Software development tools are available to
implement one or more compiler phases
–
–
–
–
–
Scanner generators (Lex and Flex)
Parser generators (Yacc and Bison)
Syntax-directed translation engines
Automatic code generators
Data-flow engines
For further details this webpage would be sufficient
http://dinosaur.compilertools.net/
COP5621 Fall 2009
9
ANTLR 3.x Project for Compiler
Construction
• This is a project that is built using Eclipse and the source
code along with all the class files are available in Java. This
aids the students in creating compiler project on a fly.
• Its C# libraries are also available that can be used.
• I would try to take a lab and discuss it
• It tutorials and videos are available at the following
address:
http://www.vimeo.com/groups/29150/videos
Recap of the last lecture
• Difference:
Skeletal Source Program
Preprocessor
Source Program
Compiler
Target Assembly Program
Assembler
Relocatable Object Code
Linker
Absolute Machine Code
Libraries and
Relocatable Object Files
11
Recap
We discussed:
• What are Regular Expressions ? How to write ?
• RE→NFA (Thompson’s construction)
• NFA →DFA (Subset construction)
The Subset Construction Algorithm
Initially, -closure(s0) is the only state in Dstates and it is unmarked
while there is an unmarked state T in Dstates do
mark T

for each input symbol a 
do
U := -closure(move(T,a))
if U is not in Dstates then
add U as an unmarked state to Dstates
end if
Dtran[T,a] := U
end do
end do
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Subset Construction Example
start
0


1
3

7
a
a
a
b
a1
2
4
b
5
b
8
b
6
a2
a3
b
C
b
start
A
b
Dstates
A = {0,1,3,7}
B = {2,4,7}
C = {8}
D = {7}
E = {5,8}
F = {6,8}
a3
a
b
D
a
a
B
a1
b
E
a3
b
F
a2 a3
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Today’s Lecture
• How can we minimize a DFA? (Hopcroft’s
Algorithm)
Section 3.9: Minimization of DFA
• What do we want to achieve?
Hopcroft’s Algorithm Pg 142
• Input:
A DFA M with set of states S, set of inputs ,
transition function defined, start state So and
set of accepting states F
• Output:
A DFA M’ accepting the same language as M
and having fewer states as possible
Algorithm 3.6
• Method:
Step1:Construct an initial partition P of the states
with two groups : the accepting states (F) and the
non accepting states (S-F)
Step2:Apply the following procedure (Construction
of Pnew) to construct a new partition (Pnew)
Procedure for Pnew construction
• For each group G of P do
partition G into subgroups such that two
states s and t are in the same subgroup if
and only if for all input symbols a, states s
and t have transitions on a to states in the
same group of P
• Replace G in Pnew by the set of all subgroups
formed
Algorithm 3.6(continue..)
• Step3: If Pnew = P and proceed to step 4 . Otherwise repeat
step 2 with P=Pnew
• Step4:Choose one state as the state representative and add
these states in M’
• Step5: If M’ has a dead state and unreachable state then
remove those states (A dead state is a non accepting state
that has transitions to itself on all inputs. An unreachable
state is any state not reachable from the start state )
• Step6: Complete
Example # 1
• The DFA for (a|b) *abb
Example # 1 (Applying Minimization)