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PROJECT PRESENTATION-2011

Sunil Kumar Patra & Debadatta Nayak Roll No:200710427 & 200710374

AGENDA

Introduction

Code Optimization

Objectives

Implemented Algorithms

Elimination Of Blank Lines & Blank Spaces

Elimination Of Unused Variables

Elimination Of Dead Functions

Elimination Of Unused Header File

Test For Program Termination

Conclusion

Recommendation for Future Improvements


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INTRDUCTION

Code optimization involves the application of rules and algorithms to

program code with the goal of making it faster, smaller, more efficient, and so

on.

Optimizations can be performed at several levels (e.g. source code,

intermediate representations), and by various parties, such as the developer or

the compiler/optimizer.

There are broadly two types of optimizations, optimizations for speed and

for memory space. Sometimes an optimization does both.


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Cont

Compilation optimization must meet, the following design

objectives:

The optimization must be correct, that is, preserve the

meaning of the compiled program.

The optimization must improve the performance of many

programs

The compilation time must be kept reasonable

The engineering effort required must be manageable.


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CODE OPTIMIZATIONS

Optimization is the process of transforming a piece of code to make more

efficient (either in terms of time or space) without changing its output or

side-effects.

The only difference visible to the codes user should be that it runs faster

and/or consumes less memory.

It is really a misnomer that the name implies we are finding an "optimal

solution in truth, optimization aims to improve, not perfect, the result.

Code optimization can be also broadly categorized as platform-dependent

and platform-independent techniques


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OBJECTIVES

Elimination of extra blank spaces, blank lines

Elimination of the variables which are not being used but declared

Elimination of dead functions

Eliminate of header file, which are not being used

Elimination of infinite loops


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//BEFORE OPTIMIZATION

1. #include

2. main() {

3. int a=2,b,c;

4. if(a ) {

5. printf(possible);

6. }

7. a= b+ c;

8.

9. printf("\nThis is a test");

10. return 0;

11. }N

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Elimination Of Extra Blank Space,blank Lines

//AFTER OPTIMIZATION

1.#include

2. main() {

3.int a,b,c;

4.if(a){

5.printf(possible);

6.}

7.a= b+ c;

8.printf("\nThis is a test");

9.return 0;

10.}


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IMPLEMENTED ALGORITHM

STEP 1: Input file:test.c (r-mode) Output File:blank.c (w-mode)

STEP 2:Scan each character(ch) upto EOF

a.if ch!=\n and ch!=\t then

check, if ch equals any of ; { } > then

write ch into blank.c

STEP 3: Open blank.c in r-mode Scan each char Upto EOF

a.if ch equals space increment the count

else if count is 1 then write space into blank1.c

b.if ch not equals space write direct into blank1.c

STEP 4: Check the output in blank1.c containing no extra blank space and blank

lines


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Elimination Of Variables Which are not being used ButDeclared

//BEFORE OPTIMIZATION

1.#include

2.main() {

3. int var1=1, var2=2, var3=3, var4=5;

4.if(var1){

5.printf(possible);

6.}

7. Var1= var2+ var3;

8. printf("\n\nthis is a testl......");

9.return 0;

10.}

//AFTER OPTIMIZATION

1.#include

2.main() {

3. int var1=1, var2=2, var3=3;4.if(var1){

5.printf(possible);

6.}

7. Var1= var2+ var3;

8. printf("\n\nthis is a testl......");

9.return 0;

10.}


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Cont..

Var1 Var2 Var3 var4Declared Variables

Var1 Var1 Var2 Va3Used Variables :

Var4Unused Variable


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ALGRITHM TO FIND DECLARED VARIABLE

STEP 1:Input File:test.c Output File :declared.c

STEP 2:Scan Each char ch from test.c upto EOF

a.if ch equals { increment count by 1

b.if ch equals ( and count >= 1 then Goto EOF

else if ch equals space

assign the file pointer to current position

1.write each ch into sec.c until ; encounters

STEP 3:Open sec.c in r-mode scan each character upto EOF

a.if ch is any alphabet (Upper and Lower Case) or Numeric(0-9) thenwrite into declared.c

else write new line char to declared.c

STEP 4: Now all declared variables are in declared.c

STEP 5:END


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ALGORITHM TO FIND USED VARIABLE AND COMPARE

STEP 1: Input : test.c

STEP 2: Read each char ch from test.c upto EOF

a. If ch equals = then move file pointer backward upto \n and forward

upto ; then write these into a file

STEP 3: Open that File and scan each chara. if any alphabet(Upper and Lower Case) and numeric char encounters

then store it to a 2-d char Array i.e usedvar[ ][ ]

STEP 4: Open declared.c in r-mode scan each char upto EOF

and store in a 2-d char Array i.e declared[ ][ ]

STEP 5: Then Compare each string from declared[ ][ ] with usedvar[ ][ ] then

the unmatched strings are Unused Variables .


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ELIMINATION OF DEAD FUNCTIONS

Dead code elimination is a compiler optimization that removes code

that does not affect the program.

Removing such code has two benefits: it shrinks program size, animportant consideration in some contexts, and it lets the running

program avoid executing irrelevant operations, which reduces its

running time.

Dead code includes code that can never be executed (unreachable

code), and code that only affects dead variables that is variables that are

irrelevant to the program.


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Cont

// BEFORE OPTIMIZATION

1. int foo(void)

2. {

3. int a = 24;

4. int b = 25;/*Assignment to

5. dead variable */

6. int c;

7. c = a


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Cont

1. #include

2. main()

3. {

4. int a , b=1,c=2,d,k;5. Char ch;

6. a=b*c;

7. b=b +2;

8. c=c+3;

9. d=a;

10. k=b;

11. return 0; }

a b c d k

Defined Variables

b c b c a b

Used Variables

d k

Dead Variables


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ELIMINATION OF UNUSED HEADER FILES

Including a header file produces the same results as copying the header file

into each source file that needs it. Such copying would be time-consuming and

error-prone.

So finally eliminating the header files which are not being used in the

program but declared can optimize the program with respect to program size

and running time.


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IMPLEMENTED ALGRITHM

STEP 1: Input File :Test.c

STEP 2: Scan Each Character ,findout each function used in test.c and write

it into a file fun_list.c

STEP 3: Except functions defined under stdio.h(main(),printf(),scanf()

.etc) and if(),for()etc write all other function into another filefun_list1.c

STEP 4: From fun_list1.c eliminate the repeated function and make single

entry of functions into another file FUN_LIST.c

STEP 5:From FUN_LIST.c,for each function findout the corresspnding

header file name by comparing with functions of standard libraries.

STEP 6: Write #include as default header into include_header.c

STEP 7: Now append the result of STEP 5 into file include_header.c

STEP 8: Hence include_header.c contains all necessery headers, so now add

rest part of source program-test.c i.e except headers into include_header.c

STEP 9:END Result : include_header.c is the optimized code of test.c i.e

without unused header files


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IMPLEMENTED ALGRITHM

1. #include

2. #include

3. #include

4. #include

5. main()

6. {7. int a,b,c;

8. char str[12];

9. scanf("%s",str);

10. a=strlen(str);

11. b=power(a);12. b=power(a);

13. printf("hi this is sunil ");

14. return 0;

15. }

main

scanf

strlen

power

power

printf

strlen

Power`

power

strlen

power

1. #include

2. #include

3. #include

4. main()

5. {6. int a,b,c;

7. char str[12];

8. scanf("%s",str);

9. a=strlen(str);

10. b=power(a);

11. b=power(a);

12. printf("hi this is sunil ");

13. return 0;

14.}

AFTER

OPTIMIZATION


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TEST FOR PROGRAM TERMINATION

An infinite loop is a sequence of instructions in a computer program

which loops endlessly.

Typically they are divided into two categories, "for loops" and "while loops

There are many patterns in code that will result in an infinite loop and different

programming languages have varying approaches.

The main aim of our program is not eliminating the infinite loops, but

detecting the cases whether an infinite loop exits in the source code itself or not.

If the source program contains an infinite loop then it will show a printed

message Infinite loop is present in the program


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ALGORITHM To Test Program TerminationHaving for Loop

Input file: test.c Output file:forinfinite.c

STEP 1: scan each character (ch)of input file upto

EOF and store the character in a array

STEP 2: if ch=='\n' or ch==';' or ch=='(' make the

array null and set i=0STEP 3: compare the string with "for"

if true then set the pointer at the current

position and scan upto the character ')'

if character is any of the symbols '>' or '=' or '


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TEST WITH while LoopInput file: test.c Output file: whileinfinite.c

STEP 1: scan each character (ch)of input file upto

EOF and store the character in a array

if ch=='\n' or ch==';' or ch=='(' make the array

null and set i=0

STEP 2: compare the string with "while"

if true then set the pointer at the current positionand scan upto the character ')'

if ch>48 && ch


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Recommendation for Future Improvements

We have focused on primary level of dead code removal i.e. dead

variable elimination only. Future work can be done on eliminating dead

functions.

In our project we have just tested the program termination using certain

infinite loop conditions. Future work can be done on automatic method to

test program termination using mathematical dependency of logic

implemented inside the loop, so as to solve the HALTING problem.


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REFERENCES

[1] Alfred V Aho , Ravi Sethi and J D Ullman, Compilers: Principles,Techniques, and Tools,vol-1 PP 125-160,Aug-2010

[2] S.Muchnick,Advanced Compiler Design and

Implementation,vol- 2 Kaufmann, 1997

[3] Byron Cook,Termination ,Microsoft Research http://research.micr

osoft.com/en-us/um/cambridge/projects/terminator

[4] Cook, B., Gotsman, A., Podelski, A., Rybalchenko, A.AND VARDI

M. Y. Proving that programs eventually do something good,

POPL, PP 1-17, 2007


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S il K P t & D b d tt N k R ll N 200710427 & 200710374

THANK YOU

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