Better control flow analyzer for loop

[codehz]

The problem:

local function test(value: isize): isize
  while true do
    -- some code (no break)
    if cond(value) then
      return value
    end
    -- another code (no break)
  end
end

got error: error: a return statement is missing before function end
but as we all know that it is impossible to break the loop without quit the whole function.

[edubart]

Thanks for reporting this case, I will look into the issue soon.

[codehz]

There is a small problem about the while true

If the loop conditions are unknown at compile time, this analysis is impossible.
However, it is too weird to determine the result of the entire control flow analysis based on whether the loop condition can be calculated at compile time. It make things inconsistency.

A possible solution is making while true as a special case of an infinite loop. In other cases, even if it can be determined at compile time(for example, taken from compile options), don't treat it as an infinite loop.

[edubart]

A possible solution is making while true as a special case of an infinite loop.

I made exactly that in commit 89435a7

That is, while true will be treated as a special case and the function will be allowed to omit the return in case the while loop does not have a break statement.