Abstract Syntax Trees & Compiler Optimizations & Three-address Codes
tegus23
JHU_SP20_CompOrg_Module9_Assignment1.pdf
Abstract Syntax Trees
Using the grammar below, construct the resulting abstract syntax tree from the code below. You may
find the following tool helpful: https://app.diagrams.net/
squared = 0
sum = 0
FOR J = 1 to 40 DO
BEGIN
squared:= J * J
sum = sum + squared
END
WRITE sum
<stmt-list> ::= <stmt> { ; <stmt> }
<stmt> ::= <assign> | <read> | <write> | <for>
<assign> ::= id = <exp>
<exp> ::= <term> { + <term> | - <term> }
<term> ::= <factor> { * <factor> | DIV <factor> }
<factor> ::= id | int | ( <exp> )
<id-list> ::= id { , id }
<for> ::= FOR <index-exp> DO <body>
<index-exp> ::= id = <exp> TO <exp>
<write> ::= WRITE ( <id-list> )
<body> ::= <stmt> | BEGIN <stmt-list> END
Compiler Optimizations & Three-address Codes
For the following piece of C code, examine each line and determine whether or not a compiler
optimization can be applied. If an optimization can be used, write the name of the optimization you would
apply if you were the compiler and, in 2-3 sentences, describe how it makes the program more efficient.
Once you’ve simplified the code, provide a list of three-address codes for the lines of source code
remaining (focus only on the relevant lines, you do not need to provide three-address codes for things
like ‘#include’ and ‘return 0’).
#include <stdio.h>
int main(void) {
bool debug = false;
int a = 0;
int b = 5;
int c = b + b;
int d = 15;
int e = b * c;
if(debug)
{
printf("Running in debug mode.");
// debug code
// debug code
// debug code
// debug code
}
a = b * c + d;
a = a * 1;
for(int i = 0; i < b; i++)
printf("i = %d\n", i+0);
for(int i = 0; i < 5; i++)
printf("%d\n", i*1);
int j = 0;
return 0;
}
- Abstract Syntax Trees
- Compiler Optimizations & Three-address Codes
