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/* NSC -- new Scala compiler
* Copyright 2005-2011 LAMP/EPFL
* @author Martin Odersky
*/
package scala.tools.nsc
package backend.icode
package analysis
/** A complete lattice.
*/
trait SemiLattice {
type Elem <: AnyRef
/** Hold together local variable and stack state. The
* equals method uses reference equality for top and bottom,
* and structural equality for other values.
*/
final case class IState[V, S](vars: V, stack: S) {
override def hashCode = vars.hashCode + stack.hashCode
override def equals(other: Any): Boolean = other match {
case x: IState[_, _] =>
if ((this eq bottom) || (this eq top) || (x eq bottom) || (x eq top)) this eq x
else stack == x.stack && vars == x.vars
case _ =>
false
}
}
/** Return the least upper bound of a and b. */
def lub2(exceptional: Boolean)(a: Elem, b: Elem): Elem
/** Return the top element. */
def top: Elem
/** Return the bottom element. */
def bottom: Elem
/** Compute the least upper bound of a list of elements. */
def lub(xs: List[Elem], exceptional: Boolean): Elem =
if (xs.isEmpty) bottom
else try xs reduceLeft lub2(exceptional)
catch { case e: LubException => Console.println("Lub on blocks: " + xs) ; throw e }
}
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