While Loop
<while-loop>
while    <cond>    do      <stat>
(lab , L1   , ,      )
 // evaluation of cond
 // to c.val 
(not , c.val, , c.val)
(goto, c.val, , L2   )
 // code of stat
(goto,      , , L1   )
(lab ,  L2  , ,      )
Rule:
Semantic action:
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