--optimize can produce non-compiling code when simplifying statements

[9382]

--optimize can cause non-compiling code, for example in the case of:

local function hi()
	if true then
		return 1
	end
	return 2
end
print(hi())

the if true then's block gets inlined. However, this causes a statement block with 2 return statements, which will never compile. Ideally, if a block collapses due to being always true and the block ends with a return or similar (break, continue, I think that's it), everything after it should not be written, though I'm not immediately sure how such a thing would be implemented. Alternatively, the if then end could be replaced with a do end

[TechHog8984]

This is an issue that I've been made aware of and tried implementing a fix but slowly dropped as I over complicated things and never stumbled upon an actually solution. Please feel free to discuss or implement any solutions you come up with, as I do not have one.

[9382]

I see 2 solutions here

1. Instead of collapsing the guaranteed if statement into the parent statlist, the if statement is replaced with a surrounding do end. This is easy to implement and removes the useless check while still producing valid code, but it's also a very minimal simplification and could be better

E.g.

local function hi()
    do
        return 1
    end
    return 2
end

2. Keep the current behaviour of moving the guaranteed to run block into the parent statlist, but check if the block moved ends in a return, break, or continue statement. If it does, remove any code that would've come after it, perhaps with a nice comment to say if something was removed. This is the best way to simplify it, but could be difficult to implement

E.g.

local function hi()
    return 1
    -- Unreachable code removed
end

[TechHog8984]

I like both. I'll go with the do end for simplicity. Thanks.

[TechHog8984]

Pushed and released, but I hope to keep the issue open so we can come back to this with a better fix.