Abstract Syntax Trees Using The Grammar Below Construct The

Abstract Syntax Treesusing The Grammar Below Construct The Resulting

Using the provided grammar, construct the abstract syntax tree (AST) from the given code snippet involving a for loop and variable assignments. Then, analyze the code for possible compiler optimizations, list them, and generate corresponding three-address code for relevant statements.

Paper For Above instruction

The provided code snippet performs a summation of squares of integers from 1 to 40, employing variables and a for loop structure. The goal is to parse this code into an abstract syntax tree (AST) according to the specified grammar, analyze potential compiler optimizations, and generate efficient three-address code for key statements.

Constructing the Abstract Syntax Tree

The provided pseudo-code is as follows:

Set squared = 0, sum = 0
For J = 1 to 40 do begin
squared := J * J
sum := sum + squared
END
Write sum

Applying the given grammar, the AST can be illustrated hierarchically as follows:

• stmt-list
  • stmt (assignment):

    assign to sum:

    • sum := sum + squared
  • stmt (for loop):
    • for:

      FOR J = 1 TO 40 DO

    • body:
      • stmt-list
        • stmt (assignment):

          squared := J * J

        • stmt (assignment):

          sum := sum + squared

  • stmt (write):

    WRITE(sum)

The AST visually captures the sequence of assignments, the for loop with its nested statements, and the output statement, adhering to the grammar rules.

Optimization Analysis and Three-address Codes

Analyzing the C code provided for compiler optimization opportunities reveals several common techniques:

1. Constant Folding: The statement a = a * 1; performs multiplication by 1, which can be optimized out as it does not alter the value. This improves efficiency by eliminating unnecessary computation.
2. Dead Code Elimination: The debug mode conditional contains print statements that execute only if debug is true. If debug is initialized as false and never changed, these statements are dead code and can be removed.
3. Loop Invariant Code Motion: The expression i+0 in the loop print statement is invariant and can be computed outside the loop to save repeated computation.
4. Redundant Computation Elimination: The expression i*1 also performs multiplication by 1, which can be optimized out.

Applying these optimizations, the code can be simplified as follows:

int a = b * c + d;        // no optimization possible
a = a;                    // multiplication by 1 eliminated
for(int i=0, offset=0; i 
printf("i = %d\n", offset); // moved invariant expression outside loop
}
for(int i=0; i 
printf("%d\n", i);
}

Corresponding three-address code snippets for the relevant parts are as follows:

Three-Address Code for Assignments

1. Compute c:

2. t1 = b * b

   t2 = 15

   a = t1 + t2

3. Compute a (since multiplication by 1 is optimized out):

4. a = a // direct assignment, no operation needed

5. Three-Address Code for Loops
7. First loop:

i = 0
L1: if i >= b goto L2
printf("i = %d\n", i)
i = i + 1
goto L1
L2:

8. Second loop:

i = 0
L3: if i >= 5 goto L4
printf("%d\n", i)
i = i + 1
goto L3
L4:

Conclusion

The analysis demonstrates how compilers can optimize redundant and invariant expressions through constant folding and loop-invariant code motion. Eliminating unnecessary calculations and dead code leads to more efficient executables. Generating three-address code provides a low-level, intermediate representation to facilitate further optimizations and targeted machine code generation. By applying such techniques, compilers significantly enhance runtime performance and resource utilization, especially for computation-intensive tasks like summations and iterative processing.

References

• Muchnick, S. S. (1997). Advanced Compiler Design and Implementation. Morgan Kaufmann.
• Compilers: Principles, Techniques, and Tools. Pearson.