Loop hoisting hoists incorrect variables

[cardillan]

Loop hoisting is broken. It doesn't hoist instructions that the loop control variable depends on, but it happily hoists instructions that change a variable which was already read by the loop, which is incorrect:

// To make the loop hoisting change more understandable
#set data-flow-optimization = none;
var a = 0;
do
    print(a);
    a = 1;
while switch1.enabled;

produces:

set .a 0
set .a 1
print .a
sensor *tmp0 switch1 @enabled
jump 2 notEqual *tmp0 false