Papyrinth Optimizations

[erri120]

From @cadpnq

• When two labels are next to one another all branches pointing at the first can be rewritten to point to the second.
• When a label is followed by a jump all branches to the label can be rewritten to point to the target of the jump.
• A label with no branches targeting it can be removed.
• All code between a jump or return and the next label is dead and can be removed.
• Branches followed by their target can be removed.
• A conditional branch pointing at an identical conditional branch can be written to point at the target of the second one.
• A conditional branch pointing at an opposite conditional branch can be written to point at just after the second branch.
• Assigning or casting something to itself can be removed.
• With the exception of function calls, any instruction storing to ::nonevar can be removed.
• A cast instruction where dest and source are of the same type can be turned into an assign instruction.
• Any instruction except function calls that store a value that is not used can be removed.
• Two groups of temporaries can be combined if they are of the same type and none of them interfere with each other.
• When a value is not'ed and only used in a branch the not can be removed and the branch can be rewritten to use the opposite condition.
• Anything storing to a temp that is only used in an assign to another variable can be rewritten to store directly to that variable.
• Any assign to a temporary that is only used in the next instruction can be removed and the next instruction rewritten to use the source of the assign.

[cadpnq]

It's worth noting that on some of these referencing labels we're talking about branch destinations. You will likely have something different, but during script loading in papyrith I convert branch offsets into references to uniquely named psuedo-instructions that I inserted into the bytecode.