code optimization techniques: a)dead code elimination b) constant propagation

###  tac.txt ###
1 := b - c
2 * b c c
3 + b a res
4 - res no1 res
5 := 322 - no
6 := no - x
7 * x c res1

###### pr_10.c ######

/*

9) WAP to implement following code optimization techniques:

   a)dead code elimination   b) constant propagation

*/

#include<stdio.h>

struct holder

{

char seqno[3],op[3],arg1[8],arg2[8],result[8];

}tac[50];

int cnt=0,i,j,k,used,isnum;

char hunted[8];

void removeline(int no)

{

for(k=no;k<=cnt;k++)

tac[k]=tac[k+1];

cnt--;

}

void eliminate_dead()

{

//if not used in future remove that line

for(i=0;i<cnt-1;i++)

{

used=0;

strcpy(hunted,tac[i].result);

for(j=i+1;j<cnt;j++)

{

if(strcmp(tac[j].arg1,hunted)==0 || strcmp(tac[j].arg2,hunted)==0)

{

used=1;

break;

}

}

if(!used)

{

printf("\n\t Removing .. %s",tac[i].seqno);

removeline(i);

i--;

}

}

}

void const_propo()

{

//hunt var1 = const and insted of var1 replece const

for(i=0;i<cnt;i++)

{

if(strcmp(tac[i].op,":=")==0 && strcmp(tac[i].arg2,"-")==0)

{

isnum=1;

for(j=0;j<strlen(tac[i].arg1);j++)

if(!isdigit(tac[i].arg1[j]))

isnum=0;

if(isnum)

{

strcpy(hunted,tac[i].result);

for(k=i+1;k<cnt;k++)

{

if(strcmp(tac[k].arg1,hunted)==0)

strcpy(tac[k].arg1,tac[i].arg1);

if(strcmp(tac[k].arg2,hunted)==0)

strcpy(tac[k].arg2,tac[i].arg1);

}

}

}

} 

}

int main()

{

FILE * fin =fopen("tac.txt","r");

int i;

while(!feof(fin))

{

fscanf(fin,"%s%s%s%s%s",tac[cnt].seqno,tac[cnt].op,tac[cnt].arg1,tac[cnt].arg2,tac[cnt].result);

cnt++;

}

cnt--;

printf("\n\t\t*** PURE INPUT ****");

printf("\n\tIndex\tOP\tArg1\tArg2\tResult");

for(i=0;i<cnt;i++)

{

printf("\n\t%s\t%s\t%s\t%s\t%s",tac[i].seqno,tac[i].op,tac[i].arg1,tac[i].arg2,tac[i].result);

}

const_propo();

printf("\n\t\t*** After Process ****");

printf("\n\tIndex\tOP\tArg1\tArg2\tResult");

for(i=0;i<cnt;i++)

{

printf("\n\t%s\t%s\t%s\t%s\t%s",tac[i].seqno,tac[i].op,tac[i].arg1,tac[i].arg2,tac[i].result);

}

printf("\n\tEnter t0 cont..");

scanf("%d",&i);

eliminate_dead();

printf("\n\t\t*** After Process ****");

printf("\n\tIndex\tOP\tArg1\tArg2\tResult");

for(i=0;i<cnt;i++)

{

printf("\n\t%s\t%s\t%s\t%s\t%s",tac[i].seqno,tac[i].op,tac[i].arg1,tac[i].arg2,tac[i].result);

}

fclose(fin);

}

### output #####

 ./a.out

*** PURE INPUT ****

Index OP Arg1 Arg2 Result

1 := b - c

2 * b c c

3 + b a res

4 - res no1 res

5 := 3 - pi

6 := pi - x

7 * x c res1

*** After Process ****

Index OP Arg1 Arg2 Result

1 := b - c

2 * b c c

3 + b a res

5 := 3 - pi

7 * 3 c res1