Intermediate Code Generator for For Loop - Compiler Design - Yacc Program

Program:

// Lex file: im4.l

alpha [A-Za-z]
digit [0-9]

%%

[\t \n]
for             return FOR;
{digit}+    return NUM;
{alpha}({alpha}|{digit})* return ID;
"<="         return LE;
">="         return GE;
"=="         return EQ;
"!="          return NE;
"||"            return OR;
"&&"         return AND;
.                return yytext[0];

%%

// Yacc file: im4.y

%{
#include <stdio.h>
#include <stdlib.h>
%}
%token ID NUM FOR LE GE EQ NE OR AND
%right "="
%left OR AND
%left '>' '<' LE GE EQ NE
%left '+' '-'
%left '*' '/'
%right UMINUS
%left '!'

%%

S       : FOR '(' E ';'{lab1();} E {lab2();}';' E {lab3();}')' E';'{lab4(); exit(0);}
         ;
E       : V '='{push();} E{codegen_assign();}
         | E '+'{push();} E{codegen();}
         | E '-'{push();} E{codegen();}
         | E '*'{push();} E{codegen();}
         | E '/'{push();} E{codegen();}
         | '(' E ')'
         | '-'{push();} E{codegen_umin();} %prec UMINUS
         | V
         | NUM{push();}
         ;
V       : ID {push();}
         ;

%%

#include "lex.yy.c"
#include<ctype.h>
char st[100][10];
int label[20];
int top=0;
char i_[2]="0";
char temp[2]="t";

int lno=0,ltop=0;
int start=1;

main()
{
    printf("Enter the expression:\n");
    yyparse();
}

push()
{
   strcpy(st[++top],yytext);
}

codegen()
{
    strcpy(temp,"t");
    strcat(temp,i_);
    printf("%s = %s %s %s\n",temp,st[top-2],st[top-1],st[top]);
    top-=2;
    strcpy(st[top],temp);
    i_[0]++;
}

codegen_umin()
{
    strcpy(temp,"t");
    strcat(temp,i_);
    printf("%s = -%s\n",temp,st[top]);
    top--;
    strcpy(st[top],temp);
    i_[0]++;
}

codegen_assign()
{
    printf("%s = %s\n",st[top-2],st[top]);
    top-=2;
}
lab1()
{
    printf("L%d: \n",lno++);
}
lab2()
{
    strcpy(temp,"t");
    strcat(temp,i_);
    printf("%s = not %s\n",temp,st[top]);
    printf("if %s goto L%d\n",temp,lno);
    i_[0]++;
    label[++ltop]=lno;
    lno++;
    printf("goto L%d\n",lno);
    label[++ltop]=lno;
    printf("L%d: \n",++lno);
 }
lab3()
{
    int x;
    x=label[ltop--];
    printf("goto L%d \n",start);
    printf("L%d: \n",x);
   
}

lab4()
{
    int x;
    x=label[ltop--];
    printf("goto L%d \n",lno);   
    printf("L%d: \n",x);
}

Output:
nn@linuxmint ~ $ lex im4.l
nn@linuxmint ~ $ yacc im4.y
conflicts: 4 shift/reduce
nn@linuxmint ~ $ gcc y.tab.c -ll -ly
nn@linuxmint ~ $ ./a.out
Enter the expression:
for(i=0;i=b;i=i+1) a=a+b;
i = 0
L0:
i = b
t0 = not i
if t0 goto L1
goto L2
L3:
t1 = i + 1
i = t1
goto L0
L2:
t2 = a + b
a = t2
goto L3
L1:
nn@linuxmint ~ $

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