GDScript: Improve IF statement performance when using logical and/or expressions

[aurpine]

Summary

Improve GDScript IF statement performance when and and or operators are used. Instead of storing the result of these logical operators, we can use jumps.

TODO

• Tests
• Proper benchmarks
• Logical not (possibly separate PR)

Problem

Currently the code

if a and b:
    pass

will compile to

 0: line 2:    if a and b:
 2: jump-if-not stack(3) to 12
 5: jump-if-not stack(4) to 12
 8: assign stack(5) = true
 10: jump 14
 12: assign stack(5) = false
 14: jump-if-not stack(5) to 21
 17: assign stack(5) = null
 19: line 3:           pass
 21: == END ==

Essentially, we are assigning the result of the condition expression to a variable before branching based on the variable. Though it is short-circuiting, the assignment happens regardless.

Solution

Instead of jumping to set a variable, we will directly jump to either the if branch or else branch (if applicable).

With the fix applied, the generated bytecode for the previous example is

 0: line 2:    if a and b:
 2: jump-if-not stack(3) to 10
 5: jump-if-not stack(4) to 10
 8: line 3:            pass
 10: == END ==

Result

Initial testing shows the change is 30-35% faster when a single operator is used.

Generated bytecode is reduced by up to 79%. Old code would add at least 14 addresses per additional operator, while the new code adds at least 3.

Future Work

Apply similar changes to:

• while
• match