Wrong codegen with while and &&

[asterite]

Given:

x = nil
y = nil

while !(x && y)
  pp x
  x = 1
end

The above code will print x # => nil forever, which is wrong because x is clearly assigned the value 1 inside the loop.

The same happens with until:

x = nil
y = nil

until x && y
  pp x
  x = 1
end

(but until exp is currently re-written to while !exp so the above is logical to happen)

Extracted from #4239

[zatherz]

Copying over from the other issue:
Using while !(a && b): https://carc.in/#/r/1t8j (unexpected behavior)
Using while !a || !b: https://carc.in/#/r/1t8n (expected behavior)
Using while !(Glob.a && b) (Glob is a class): https://carc.in/#/r/1t8p (expected behavior)
Using while !Glob.a || !b (same result): https://carc.in/#/r/1t8q (expected behavior)
Using while !(a && b), assigning a to Glob.a: https://carc.in/#/r/1t8r (unexpected behavior with a, expected behavior with Glob.a)
Using while !(a && b), assigning a to Glob.a: https://carc.in/#/r/1t8s (expected behavior with both a and Glob.a)

To sum it up, it seems like setting the value of a in the scope of a while !(a && b) actually creates a new local variable instead of modifying the one in the outer scope, while while !a || !b has the expected result of modifying the local variable in the outer scope.

EDIT:
First test, but printing the value of a after the loop: https://carc.in/#/r/1t8u
Actually, it does change the variable of the outer scope, but the value of a at the beginning of the scope of each loop is set back to the initial value before the loop?

EDIT 2:
Expanding the while condition of the first test from !(a && b) to !((a != nil) && b) produces expected behavior: https://carc.in/#/r/1t90
But, expanding the condition from !(a && b) to !(!a.nil? && b) retains the unexpected effect: https://carc.in/#/r/1t92