[refactor] move some logic-related code

src/compiler/scala/tools/nsc/transform/patmat/Logic.scala

@@ -52,7 +52,8 @@ trait Logic { self: PatternMatching =>
 
   // http://www.cis.upenn.edu/~cis510/tcl/chap3.pdf
   // http://users.encs.concordia.ca/~ta_ahmed/ms_thesis.pdf
-  trait FirstOrderLogic {
+  // propositional logic with constants and equality
+  trait PropositionalLogic {
     class Prop
     case class Eq(p: Var, q: Const) extends Prop
 
@@ -297,7 +298,7 @@ trait Logic { self: PatternMatching =>
     def findAllModelsFor(f: Formula): List[Model]
   }
 
-  trait CNF extends FirstOrderLogic {
+  trait CNF extends PropositionalLogic {
 
     /** Override Array creation for efficiency (to not go through reflection). */
     private implicit val clauseTag: scala.reflect.ClassTag[Clause] = new scala.reflect.ClassTag[Clause] {
@@ -404,7 +405,6 @@ trait Logic { self: PatternMatching =>
 //      patmatDebug("cnf for\n"+ p +"\nis:\n"+cnfString(res))
       res
     }
-
   }
 
   trait DPLLSolver extends CNF {
@@ -524,4 +524,335 @@ trait Logic { self: PatternMatching =>
         satisfiableWithModel
     }
   }
+
+  trait TreesAndTypesDomain extends PropositionalLogic with CheckableTreeAndTypeAnalysis {
+    // resets hash consing -- only supposed to be called by TreeMakersToProps
+    def prepareNewAnalysis(): Unit = { Var.resetUniques(); Const.resetUniques() }
+
+    object Var extends VarExtractor {
+      private var _nextId = 0
+      def nextId = {_nextId += 1; _nextId}
+
+      def resetUniques() = {_nextId = 0; uniques.clear()}
+      private val uniques = new mutable.HashMap[Tree, Var]
+      def apply(x: Tree): Var = uniques getOrElseUpdate(x, new Var(x, x.tpe))
+      def unapply(v: Var) = Some(v.path)
+    }
+    class Var(val path: Tree, staticTp: Type) extends AbsVar {
+      private[this] val id: Int = Var.nextId
+
+      // private[this] var canModify: Option[Array[StackTraceElement]] = None
+      private[this] def ensureCanModify() = {} //if (canModify.nonEmpty) patmatDebug("BUG!"+ this +" modified after having been observed: "+ canModify.get.mkString("\n"))
+
+      private[this] def observed() = {} //canModify = Some(Thread.currentThread.getStackTrace)
+
+      // don't access until all potential equalities have been registered using registerEquality
+      private[this] val symForEqualsTo = new mutable.HashMap[Const, Sym]
+
+      // when looking at the domain, we only care about types we can check at run time
+      val staticTpCheckable: Type = checkableType(staticTp)
+
+      private[this] var _mayBeNull = false
+      def registerNull(): Unit = { ensureCanModify; if (NullTp <:< staticTpCheckable) _mayBeNull = true }
+      def mayBeNull: Boolean = _mayBeNull
+
+      // case None => domain is unknown,
+      // case Some(List(tps: _*)) => domain is exactly tps
+      // we enumerate the subtypes of the full type, as that allows us to filter out more types statically,
+      // once we go to run-time checks (on Const's), convert them to checkable types
+      // TODO: there seems to be bug for singleton domains (variable does not show up in model)
+      lazy val domain: Option[Set[Const]] = {
+        val subConsts = enumerateSubtypes(staticTp).map{ tps =>
+          tps.toSet[Type].map{ tp =>
+            val domainC = TypeConst(tp)
+            registerEquality(domainC)
+            domainC
+          }
+        }
+
+        val allConsts =
+          if (mayBeNull) {
+            registerEquality(NullConst)
+            subConsts map (_ + NullConst)
+          } else
+            subConsts
+
+        observed; allConsts
+      }
+
+      // populate equalitySyms
+      // don't care about the result, but want only one fresh symbol per distinct constant c
+      def registerEquality(c: Const): Unit = {ensureCanModify; symForEqualsTo getOrElseUpdate(c, Sym(this, c))}
+
+      // return the symbol that represents this variable being equal to the constant `c`, if it exists, otherwise False (for robustness)
+      // (registerEquality(c) must have been called prior, either when constructing the domain or from outside)
+      def propForEqualsTo(c: Const): Prop = {observed; symForEqualsTo.getOrElse(c, False)}
+
+      // [implementation NOTE: don't access until all potential equalities have been registered using registerEquality]p
+      /** the information needed to construct the boolean proposition that encods the equality proposition (V = C)
+       *
+       * that models a type test pattern `_: C` or constant pattern `C`, where the type test gives rise to a TypeConst C,
+       * and the constant pattern yields a ValueConst C
+       *
+       * for exhaustivity, we really only need implication (e.g., V = 1 implies that V = 1 /\ V = Int, if both tests occur in the match,
+       * and thus in this variable's equality symbols), but reachability also requires us to model things like V = 1 precluding V = "1"
+       */
+      lazy val implications = {
+        /** when we know V = C, which other equalities must hold
+         *
+         * in general, equality to some type implies equality to its supertypes
+         * (this multi-valued kind of equality is necessary for unreachability)
+         * note that we use subtyping as a model for implication between instanceof tests
+         * i.e., when S <:< T we assume x.isInstanceOf[S] implies x.isInstanceOf[T]
+         * unfortunately this is not true in general (see e.g. SI-6022)
+         */
+        def implies(lower: Const, upper: Const): Boolean =
+          // values and null
+            lower == upper ||
+          // type implication
+            (lower != NullConst && !upper.isValue &&
+             instanceOfTpImplies(if (lower.isValue) lower.wideTp else lower.tp, upper.tp))
+
+          // if(r) patmatDebug("implies    : "+(lower, lower.tp, upper, upper.tp))
+          // else  patmatDebug("NOT implies: "+(lower, upper))
+
+
+        /** does V = C preclude V having value `other`?
+         (1) V = null is an exclusive assignment,
+         (2) V = A and V = B, for A and B value constants, are mutually exclusive unless A == B
+             we err on the safe side, for example:
+               - assume `val X = 1; val Y = 1`, then
+                 (2: Int) match { case X => case Y =>  <falsely considered reachable>  }
+               - V = 1 does not preclude V = Int, or V = Any, it could be said to preclude V = String, but we don't model that
+
+         (3) for types we could try to do something fancy, but be conservative and just say no
+         */
+        def excludes(a: Const, b: Const): Boolean =
+          a != b && ((a == NullConst || b == NullConst) || (a.isValue && b.isValue))
+
+          // if(r) patmatDebug("excludes    : "+(a, a.tp, b, b.tp))
+          // else  patmatDebug("NOT excludes: "+(a, b))
+
+/*
+[ HALF BAKED FANCINESS: //!equalitySyms.exists(common => implies(common.const, a) && implies(common.const, b)))
+ when type tests are involved, we reason (conservatively) under a closed world assumption,
+ since we are really only trying to counter the effects of the symbols that we introduce to model type tests
+ we don't aim to model the whole subtyping hierarchy, simply to encode enough about subtyping to do unreachability properly
+
+ consider the following hierarchy:
+
+    trait A
+    trait B
+    trait C
+    trait AB extends B with A
+
+  // two types are mutually exclusive if there is no equality symbol whose constant implies both
+  object Test extends App {
+    def foo(x: Any) = x match {
+      case _ : C  => println("C")
+      case _ : AB => println("AB")
+      case _ : (A with B) => println("AB'")
+      case _ : B  => println("B")
+      case _ : A  => println("A")
+    }
+
+ of course this kind of reasoning is not true in general,
+ but we can safely pretend types are mutually exclusive as long as there are no counter-examples in the match we're analyzing}
+*/
+
+        val excludedPair = new mutable.HashSet[ExcludedPair]
+
+        case class ExcludedPair(a: Const, b: Const) {
+          override def equals(o: Any) = o match {
+            case ExcludedPair(aa, bb) => (a == aa && b == bb) || (a == bb && b == aa)
+            case _ => false
+          }
+          // make ExcludedPair(a, b).hashCode == ExcludedPair(b, a).hashCode
+          override def hashCode = a.hashCode ^ b.hashCode
+        }
+
+        equalitySyms map { sym =>
+          // if we've already excluded the pair at some point (-A \/ -B), then don't exclude the symmetric one (-B \/ -A)
+          // (nor the positive implications -B \/ A, or -A \/ B, which would entail the equality axioms falsifying the whole formula)
+          val todo = equalitySyms filterNot (b => (b.const == sym.const) || excludedPair(ExcludedPair(b.const, sym.const)))
+          val (excluded, notExcluded) = todo partition (b => excludes(sym.const, b.const))
+          val implied = notExcluded filter (b => implies(sym.const, b.const))
+
+          patmatDebug("eq axioms for: "+ sym.const)
+          patmatDebug("excluded: "+ excluded)
+          patmatDebug("implied: "+ implied)
+
+          excluded foreach { excludedSym => excludedPair += ExcludedPair(sym.const, excludedSym.const)}
+
+          (sym, implied, excluded)
+        }
+      }
+
+      // accessing after calling registerNull will result in inconsistencies
+      lazy val domainSyms: Option[Set[Sym]] = domain map { _ map symForEqualsTo }
+
+      lazy val symForStaticTp: Option[Sym]  = symForEqualsTo.get(TypeConst(staticTpCheckable))
+
+      // don't access until all potential equalities have been registered using registerEquality
+      private lazy val equalitySyms = {observed; symForEqualsTo.values.toList}
+
+      // don't call until all equalities have been registered and registerNull has been called (if needed)
+      def describe = {
+        def domain_s = domain match {
+          case Some(d) => d mkString (" ::= ", " | ", "// "+ symForEqualsTo.keys)
+          case _       => symForEqualsTo.keys mkString (" ::= ", " | ", " | ...")
+        }
+        s"$this: ${staticTp}${domain_s} // = $path"
+      }
+      override def toString = "V"+ id
+    }
+
+
+    import global.{ConstantType, Constant, SingletonType, Literal, Ident, singleType}
+    import global.definitions.{AnyClass, UnitClass}
+
+
+    // all our variables range over types
+    // a literal constant becomes ConstantType(Constant(v)) when the type allows it (roughly, anyval + string + null)
+    // equality between variables: SingleType(x) (note that pattern variables cannot relate to each other -- it's always patternVar == nonPatternVar)
+    object Const {
+      def resetUniques() = {_nextTypeId = 0; _nextValueId = 0; uniques.clear() ; trees.clear()}
+
+      private var _nextTypeId = 0
+      def nextTypeId = {_nextTypeId += 1; _nextTypeId}
+
+      private var _nextValueId = 0
+      def nextValueId = {_nextValueId += 1; _nextValueId}
+
+      private val uniques = new mutable.HashMap[Type, Const]
+      private[TreesAndTypesDomain] def unique(tp: Type, mkFresh: => Const): Const =
+        uniques.get(tp).getOrElse(
+          uniques.find {case (oldTp, oldC) => oldTp =:= tp} match {
+            case Some((_, c)) =>
+              patmatDebug("unique const: "+ (tp, c))
+              c
+            case _ =>
+              val fresh = mkFresh
+              patmatDebug("uniqued const: "+ (tp, fresh))
+              uniques(tp) = fresh
+              fresh
+          })
+
+      private val trees = mutable.HashSet.empty[Tree]
+
+      // hashconsing trees (modulo value-equality)
+      private[TreesAndTypesDomain] def uniqueTpForTree(t: Tree): Type =
+        // a new type for every unstable symbol -- only stable value are uniqued
+        // technically, an unreachable value may change between cases
+        // thus, the failure of a case that matches on a mutable value does not exclude the next case succeeding
+        // (and thuuuuus, the latter case must be considered reachable)
+        if (!t.symbol.isStable) t.tpe.narrow
+        else trees find (a => a.correspondsStructure(t)(sameValue)) match {
+          case Some(orig) =>
+            patmatDebug("unique tp for tree: "+ (orig, orig.tpe))
+            orig.tpe
+          case _ =>
+            // duplicate, don't mutate old tree (TODO: use a map tree -> type instead?)
+            val treeWithNarrowedType = t.duplicate setType t.tpe.narrow
+            patmatDebug("uniqued: "+ (t, t.tpe, treeWithNarrowedType.tpe))
+            trees += treeWithNarrowedType
+            treeWithNarrowedType.tpe
+        }
+    }
+
+    sealed abstract class Const {
+      def tp: Type
+      def wideTp: Type
+
+      def isAny = wideTp.typeSymbol == AnyClass
+      def isValue: Boolean //= tp.isStable
+
+      // note: use reference equality on Const since they're hash-consed (doing type equality all the time is too expensive)
+      // the equals inherited from AnyRef does just this
+    }
+
+    // find most precise super-type of tp that is a class
+    // we skip non-class types (singleton types, abstract types) so that we can
+    // correctly compute how types relate in terms of the values they rule out
+    // e.g., when we know some value must be of type T, can it still be of type S? (this is the positive formulation of what `excludes` on Const computes)
+    // since we're talking values, there must have been a class involved in creating it, so rephrase our types in terms of classes
+    // (At least conceptually: `true` is an instance of class `Boolean`)
+    private def widenToClass(tp: Type): Type =
+      if (tp.typeSymbol.isClass) tp
+      else tp.baseType(tp.baseClasses.head)
+
+    object TypeConst extends TypeConstExtractor {
+      def apply(tp: Type) = {
+        if (tp =:= NullTp) NullConst
+        else if (tp.isInstanceOf[SingletonType]) ValueConst.fromType(tp)
+        else Const.unique(tp, new TypeConst(tp))
+      }
+      def unapply(c: TypeConst): Some[Type] = Some(c.tp)
+    }
+
+    // corresponds to a type test that does not imply any value-equality (well, except for outer checks, which we don't model yet)
+    sealed class TypeConst(val tp: Type) extends Const {
+      assert(!(tp =:= NullTp))
+      /*private[this] val id: Int = */ Const.nextTypeId
+
+      val wideTp = widenToClass(tp)
+      def isValue = false
+      override def toString = tp.toString //+"#"+ id
+    }
+
+    // p is a unique type or a constant value
+    object ValueConst extends ValueConstExtractor {
+      def fromType(tp: Type) = {
+        assert(tp.isInstanceOf[SingletonType])
+        val toString = tp match {
+          case ConstantType(c) => c.escapedStringValue
+          case _ => tp.toString
+        }
+        Const.unique(tp, new ValueConst(tp, tp.widen, toString))
+      }
+      def apply(p: Tree) = {
+        val tp = p.tpe.normalize
+        if (tp =:= NullTp) NullConst
+        else {
+          val wideTp = widenToClass(tp)
+
+          val narrowTp =
+            if (tp.isInstanceOf[SingletonType]) tp
+            else p match {
+              case Literal(c) =>
+                if (c.tpe.typeSymbol == UnitClass) c.tpe
+                else ConstantType(c)
+              case Ident(_) if p.symbol.isStable =>
+                // for Idents, can encode uniqueness of symbol as uniqueness of the corresponding singleton type
+                // for Selects, which are handled by the next case, the prefix of the select varies independently of the symbol (see pos/virtpatmat_unreach_select.scala)
+                singleType(tp.prefix, p.symbol)
+              case _ =>
+                Const.uniqueTpForTree(p)
+            }
+
+          val toString =
+            if (hasStableSymbol(p)) p.symbol.name.toString // tp.toString
+            else p.toString //+"#"+ id
+
+          Const.unique(narrowTp, new ValueConst(narrowTp, checkableType(wideTp), toString)) // must make wide type checkable so that it is comparable to types from TypeConst
+        }
+      }
+    }
+    sealed class ValueConst(val tp: Type, val wideTp: Type, override val toString: String) extends Const {
+      // patmatDebug("VC"+(tp, wideTp, toString))
+      assert(!(tp =:= NullTp)) // TODO: assert(!tp.isStable)
+      /*private[this] val id: Int = */Const.nextValueId
+      def isValue = true
+    }
+
+
+    lazy val NullTp = ConstantType(Constant(null))
+    case object NullConst extends Const {
+      def tp     = NullTp
+      def wideTp = NullTp
+
+      def isValue = true
+      override def toString = "null"
+    }
+  }
 }