Add rule for splitting ifs in predicates

src/main/scala/leon/synthesis/Rules.scala

@@ -18,6 +18,7 @@ object Rules {
     OnePoint,
     Ground,
     CaseSplit,
+    IfSplit,
     UnusedInput,
     UnconstrainedOutput,
     OptimisticGround,

src/main/scala/leon/synthesis/rules/IfSplit.scala

+/* Copyright 2009-2014 EPFL, Lausanne */
+
+package leon
+package synthesis
+package rules
+
+import purescala.Trees._
+import purescala.TreeOps._
+import purescala.Extractors._
+
+case object IfSplit extends Rule("If-Split") {
+  def instantiateOn(sctx: SynthesisContext, p: Problem): Traversable[RuleInstantiation] = {
+    val ifs = collect{
+      case i: IfExpr => Set(i)
+      case _ => Set[IfExpr]()
+    }(p.phi)
+
+    ifs.toList match {
+      case i :: _ =>
+        List(split(i, p, "Split top-level If"))
+      case _ =>
+        Nil
+    }
+  }
+
+  def split(i: IfExpr, p: Problem, description: String): RuleInstantiation = {
+    val subs = List(
+      Problem(p.as, And(p.pc, i.cond), replace(Map(i -> i.thenn), p.pc), p.xs),
+      Problem(p.as, And(p.pc, Not(i.cond)), replace(Map(i -> i.elze), p.pc), p.xs)
+    )
+
+    val onSuccess: List[Solution] => Option[Solution] = {
+      case sols if sols.size == 2 =>
+        val List(ts, es) = sols
+
+        val pre = Or(And(i.cond, ts.pre), And(Not(i.cond), es.pre))
+        val defs = ts.defs ++ es.defs
+        val term = IfExpr(i.cond, ts.term, es.term)
+
+        Some(Solution(pre, defs, term))
+
+      case _ =>
+        None
+    }
+
+    RuleInstantiation.immediateDecomp(p, this, subs, onSuccess, description)
+  }
+}
+