IfRedundantLinesRemovalTransformation.md

If Statement Redundant Lines Removal Transformation

Overview

The goal of this transformation is to extract all common lines from if-else branches and move them before or after the statement.

Example

Before:

s = input()

if s:
    a = 2
    b = a + a
    print('foo')
    x = 1
    y = x
    print(y)
else:
    a = 2
    b = a + a
    print('bar')
    x = 1
    y = x
    print(y)

After:

s = input()

a = 2
b = a + a
if s:
    print('foo')
else:
    print('bar')
x = 1
y = x
print(y)

Algorithm

1. Traverse the AST and find the node which represents the if statement

2. Calculate the length of the common suffix and prefix

3. Move the common suffix and prefix before or after the operator respectively

4. Remove the common parts from the if operator

5. Validate the new if operator

Exceptions

• If the common part is in the middle of the statements list the statement does not change, because in this case, the length of the common suffix and prefix is zero. An example of unchanged code:

s = input()

if s:
    print('foo')
    a = 2
    b = a + a
    print('bar')
else:
    print('foo1')
    a = 2
    b = a + a
    print('bar1')

• The PyStatment comparison is done using the textMatches function, which compares the text within these statements