TYPE

  VarVarPair = Var * Var
  VarVarPairSet = set(VarVarPair)
  VarVarPairSetLifted = lift(VarVarPairSet)

PROBLEM Copy_Propagation

  direction  : forward
  carrier    : VarVarPairSetLifted
  init       : top
  init_start : lift({})
  combine    : glb

TRANSFER

  ASSIGN(var, exp) =  
    let entry <= @ in
      lift(entry - { varpair | varpair in entry; 
			       varpair#1 = var || varpair#2 = var }
	         + (if expType(exp) = "VAR" then {(var,expVar(exp))} else {} endif))

/* could test whether (x,y) is in carrier while given y:=x, and not kill (x,y) */
/* could also test for x := y; z:=x;  (z is now both a copy of y and x!) */