diff --git a/common/src/main/scala/scalan/package.scala b/common/src/main/scala/scalan/package.scala
index ab705c62e8..f89cc78d53 100644
--- a/common/src/main/scala/scalan/package.scala
+++ b/common/src/main/scala/scalan/package.scala
@@ -5,5 +5,19 @@ package object scalan {
   /** Allows implicit resolution to find appropriate instance of ClassTag in
     * the scope where RType is implicitly available. */
   implicit def rtypeToClassTag[A](implicit t: RType[A]): ClassTag[A] = t.classTag
-  
+
+  /** Immutable empty array of integers, should be used instead of allocating new empty arrays. */
+  val EmptyArrayOfInt = Array.empty[Int]
+
+  /** Immutable empty Seq[Int] backed by empty array.
+    * You should prefer using it instead of `Seq[Int]()` or `Seq.empty[Int]`
+    */
+  val EmptySeqOfInt: Seq[Int] = EmptyArrayOfInt
+
+  /** Create a new empty buffer around pre-allocated empty array.
+    * This method is preferred, rather that creating empty debox.Buffer directly
+    * because it allows to avoid allocation of the empty array.
+    */
+  def emptyDBufferOfInt: debox.Buffer[Int] = debox.Buffer.unsafe(EmptyArrayOfInt)
+
 }
diff --git a/common/src/main/scala/scalan/util/CollectionUtil.scala b/common/src/main/scala/scalan/util/CollectionUtil.scala
index bba14c516f..db16c17088 100644
--- a/common/src/main/scala/scalan/util/CollectionUtil.scala
+++ b/common/src/main/scala/scalan/util/CollectionUtil.scala
@@ -61,6 +61,7 @@ object CollectionUtil {
     res.toMap
   }
 
+  // TODO optimize: using cfor and avoiding allocations
   def joinSeqs[O, I, K](outer: GenIterable[O], inner: GenIterable[I])(outKey: O=>K, inKey: I=>K): GenIterable[(O,I)] = {
     val kvs = createMultiMap(inner.map(i => (inKey(i), i)))
     val res = outer.flatMap(o => {
diff --git a/core/src/main/scala/scalan/Base.scala b/core/src/main/scala/scalan/Base.scala
index 75b0b0a5de..d151bbeb0c 100644
--- a/core/src/main/scala/scalan/Base.scala
+++ b/core/src/main/scala/scalan/Base.scala
@@ -9,6 +9,7 @@ import scalan.compilation.GraphVizConfig
 import scalan.util.StringUtil
 import debox.{Buffer => DBuffer}
 import spire.syntax.all.cfor
+import scala.collection.mutable
 
 /**
   * The Base trait houses common AST nodes. It also manages a list of encountered definitions which
@@ -92,7 +93,7 @@ abstract class Base { scalan: Scalan =>
         _elements(i + 1) = element
         Def.extractSyms(element, symsBuf)
       }
-      _syms = symsBuf.toArray()
+      _syms = if (symsBuf.length > 0) symsBuf.toArray() else EmptyArrayOfSym
     }
 
     /** References to other nodes in this Def instance.
@@ -236,7 +237,7 @@ abstract class Base { scalan: Scalan =>
       override def mirror(t: Transformer): Ref[T] = self
     }
 
-    /** Describes lifting data values of type ST (Source Type) to IR nodes of the correspoding staged type T.
+    /** Describes lifting data values of type ST (Source Type) to IR nodes of the corresponding staged type T.
       * In general T is different type obtained by virtualization procedure from ST.
       * However ST can be the same as T as is the case for Byte, Int, String etc.
       */
@@ -452,22 +453,28 @@ abstract class Base { scalan: Scalan =>
     /** Transform a sequence of nodes into new sequence of nodes. */
     final def apply[A](xs: Seq[Ref[A]]): Seq[Ref[A]] = {
       val len = xs.length
-      val res = new Array[Ref[A]](len)
-      cfor(0)(_ < len, _ + 1) { i =>
-        res(i) = apply(xs(i))
+      if (len == 0) EmptySeqOfSym.asInstanceOf[Seq[Ref[A]]]
+      else {
+        val res = new Array[Ref[A]](len)
+        cfor(0)(_ < len, _ + 1) { i =>
+          res(i) = apply(xs(i))
+        }
+        res
       }
-      res
     }
     /** Apply this transformer to the nodes present in the sequence,
       * and leave non-Ref items unchanged. */
     final def apply(xs: Seq[Any])(implicit o: Overloaded1): Seq[Any] = {
       val len = xs.length
-      val res = new Array[Any](len)
-      cfor(0)(_ < len, _ + 1) { i =>
-        val x = xs(i) match { case s: Ref[_] => apply(s); case s => s }
-        res(i) = x
+      if (len == 0) mutable.WrappedArray.empty
+      else {
+        val res = new Array[Any](len)
+        cfor(0)(_ < len, _ + 1) { i =>
+          val x = xs(i) match { case s: Ref[_] => apply(s); case s => s }
+          res(i) = x
+        }
+        res
       }
-      res
     }
 
     def +[A](key: Sym, value: Sym): Transformer
@@ -815,5 +822,23 @@ abstract class Base { scalan: Scalan =>
     } while (res != currSym)
     res
   }
-}
 
+  /** Immutable empty array of symbols, can be used to avoid unnecessary allocations. */
+  val EmptyArrayOfSym = Array.empty[Sym]
+
+  /** Immutable empty Seq, can be used to avoid unnecessary allocations. */
+  val EmptySeqOfSym: Seq[Sym] = EmptyArrayOfSym
+
+  /** Create a new empty buffer around pre-allocated empty array.
+    * This method is preferred, rather that creating empty debox.Buffer directly
+    * because it allows to avoid allocation of the empty array.
+    */
+  @inline final def emptyDBufferOfSym: DBuffer[Sym] = DBuffer.unsafe(EmptyArrayOfSym)
+
+  /** Used internally in IR and should be used with care since it is mutable.
+    * At the same time, it is used in the hotspot and allows to avoid roughly tens of
+    * thousands of allocations per second.
+    * WARNING: Mutations of this instance can lead to undefined behavior.
+    */
+  protected val EmptyDSetOfInt: debox.Set[Int] = debox.Set.empty
+}
diff --git a/core/src/main/scala/scalan/Scalan.scala b/core/src/main/scala/scalan/Scalan.scala
index 9ce1599469..c2e9359261 100644
--- a/core/src/main/scala/scalan/Scalan.scala
+++ b/core/src/main/scala/scalan/Scalan.scala
@@ -1,8 +1,7 @@
 package scalan
 
-import scalan.compilation.GraphVizExport
 import scalan.primitives._
-import scalan.staged.{Transforming}
+import scalan.staged.Transforming
 
 /** Aggregate cake with all inter-dependent modules assembled together.
   * Each instance of this class contains independent IR context, thus many
@@ -30,7 +29,6 @@ class Scalan
   with Functions
   with IfThenElse
   with Transforming
-//  with GraphVizExport
   with Thunks
   with Entities
   with Modules
diff --git a/core/src/main/scala/scalan/TypeDescs.scala b/core/src/main/scala/scalan/TypeDescs.scala
index 9b669e3311..b63d49c2bb 100644
--- a/core/src/main/scala/scalan/TypeDescs.scala
+++ b/core/src/main/scala/scalan/TypeDescs.scala
@@ -81,7 +81,7 @@ abstract class TypeDescs extends Base { self: Scalan =>
 //    }
 //  }
 
-  // TODO optimize performance hot spot (45% of invokeUnlifted time)
+  // TODO optimize performance hot spot (45% of invokeUnlifted time), reduce allocation of Some
   final def getSourceValues(dataEnv: DataEnv, forWrapper: Boolean, stagedValues: AnyRef*): Seq[AnyRef] = {
     import OverloadHack._
     val limit = stagedValues.length
@@ -151,7 +151,7 @@ abstract class TypeDescs extends Base { self: Scalan =>
       !!!(s"Cannot get Liftable instance for $this")
 
     final lazy val sourceType: RType[_] = liftable.sourceType
-    protected def collectMethods: Map[Method, MethodDesc] = Map()
+    protected def collectMethods: Map[Method, MethodDesc] = Map() // TODO optimize: all implementations
     protected lazy val methods: Map[Method, MethodDesc] = collectMethods
 
     // TODO benchamrk against the version below it
@@ -244,6 +244,7 @@ abstract class TypeDescs extends Base { self: Scalan =>
         m.getName
     }
 
+    // TODO optimize
     /** Build a mapping between methods of staged class and the corresponding methods of source class.
       * The methods are related using names.
       * The computed mapping can be used to project MethodCalls IR nodes back to the corresponding
diff --git a/core/src/main/scala/scalan/primitives/Equal.scala b/core/src/main/scala/scalan/primitives/Equal.scala
index 32dc525f89..e2a35acf15 100644
--- a/core/src/main/scala/scalan/primitives/Equal.scala
+++ b/core/src/main/scala/scalan/primitives/Equal.scala
@@ -4,10 +4,14 @@ import scalan.{Base, Scalan}
 
 trait Equal extends Base { self: Scalan =>
   /** Binary operation representing structural equality between arguments. */
-  case class Equals[A: Elem]() extends BinOp[A, Boolean]("==", equalValues[A](_, _))
+  case class Equals[A: Elem]() extends BinOp[A, Boolean]("==") {
+    override def applySeq(x: A, y: A): Boolean = equalValues[A](x, y)
+  }
 
   /** Binary operation representing structural inequality between arguments. */
-  case class NotEquals[A: Elem]() extends BinOp[A, Boolean]("!=", !equalValues[A](_, _))
+  case class NotEquals[A: Elem]() extends BinOp[A, Boolean]("!=") {
+    override def applySeq(x: A, y: A): Boolean = !equalValues[A](x, y)
+  }
 
   protected def equalValues[A](x: Any, y: Any)(implicit eA: Elem[A]) = x == y
 
diff --git a/core/src/main/scala/scalan/primitives/Functions.scala b/core/src/main/scala/scalan/primitives/Functions.scala
index 1fc9844344..0acad6ca81 100644
--- a/core/src/main/scala/scalan/primitives/Functions.scala
+++ b/core/src/main/scala/scalan/primitives/Functions.scala
@@ -4,7 +4,7 @@ import java.util
 
 import scalan.staged.ProgramGraphs
 import scalan.util.GraphUtil
-import scalan.{Lazy, Base, Nullable, Scalan}
+import scalan.{Nullable, emptyDBufferOfInt, Base, Lazy, Scalan}
 import debox.{Buffer => DBuffer}
 
 import scala.language.implicitConversions
@@ -120,7 +120,7 @@ trait Functions extends Base with ProgramGraphs { self: Scalan =>
 
     override lazy val  scheduleIds: DBuffer[Int] = {
       val sch = if (isIdentity)
-        DBuffer.ofSize[Int](0)
+        emptyDBufferOfInt
       else {
         // graph g will contain all Defs reified as part of this Lambda, (due to `filterNode`)
         // BUT not all of them depend on boundVars, thus we need to filter them out
@@ -165,15 +165,6 @@ trait Functions extends Base with ProgramGraphs { self: Scalan =>
     }
 
     override protected def getDeps: Array[Sym] = freeVars.toArray
-
-    def isGlobalLambda: Boolean = {
-      freeVars.forall { x =>
-        x.isConst || {
-          val xIsGlobalLambda = x.isLambda && { val lam = x.node.asInstanceOf[Lambda[_, _]]; lam.isGlobalLambda }
-          xIsGlobalLambda
-        }
-      }
-    }
   }
 
   type LambdaData[A,B] = (Lambda[A,B], Nullable[Ref[A] => Ref[B]], Ref[A], Ref[B])
diff --git a/core/src/main/scala/scalan/primitives/LogicalOps.scala b/core/src/main/scala/scalan/primitives/LogicalOps.scala
index fd71800d95..e81b546139 100644
--- a/core/src/main/scala/scalan/primitives/LogicalOps.scala
+++ b/core/src/main/scala/scalan/primitives/LogicalOps.scala
@@ -2,17 +2,34 @@ package scalan.primitives
 
 import scalan.{Base, Scalan}
 
+/** Slice in Scala cake with definitions of logical operations. */
 trait LogicalOps extends Base { self: Scalan =>
-  val And = new EndoBinOp[Boolean]("&&", _ && _)
+  /** Logical AND binary operation. */
+  val And = new EndoBinOp[Boolean]("&&") {
+    override def applySeq(x: Boolean, y: Boolean): Boolean = x && y
+  }
 
-  val Or = new EndoBinOp[Boolean]("||", _ || _)
+  /** Logical AND binary operation. */
+  val Or = new EndoBinOp[Boolean]("||") {
+    override def applySeq(x: Boolean, y: Boolean): Boolean = x || y
+  }
 
-  val Not = new EndoUnOp[Boolean]("!", !_)
+  /** Logical NOT unary operation. */
+  val Not = new EndoUnOp[Boolean]("!") {
+    override def applySeq(x: Boolean): Boolean = !x
+  }
 
-  val BinaryXorOp = new EndoBinOp[Boolean]("^", _ ^ _)
+  /** Logical XOR binary operation. */
+  val BinaryXorOp = new EndoBinOp[Boolean]("^") {
+    override def applySeq(x: Boolean, y: Boolean): Boolean = x ^ y
+  }
 
-  val BooleanToInt = new UnOp[Boolean, Int]("ToInt", if (_) 1 else 0)
+  /** Boolean to Int conversion unary operation. */
+  val BooleanToInt = new UnOp[Boolean, Int]("ToInt") {
+    override def applySeq(x: Boolean): Int = if (x) 1 else 0
+  }
 
+  /** Extension methods over `Ref[Boolean]`. */
   implicit class RepBooleanOps(value: Ref[Boolean]) {
     def &&(y: Ref[Boolean]): Ref[Boolean] = And(value, y)
     def ||(y: Ref[Boolean]): Ref[Boolean] = Or(value, y)
@@ -26,6 +43,7 @@ trait LogicalOps extends Base { self: Scalan =>
   }
 
 
+  /** Helper method which defines rewriting rules with boolean constants. */
   @inline
   final def rewriteBoolConsts(lhs: Sym, rhs: Sym, ifTrue: Sym => Sym, ifFalse: Sym => Sym, ifEqual: Sym => Sym, ifNegated: Sym => Sym): Sym =
     lhs match {
diff --git a/core/src/main/scala/scalan/primitives/NumericOps.scala b/core/src/main/scala/scalan/primitives/NumericOps.scala
index 70216627d4..deca140dc4 100644
--- a/core/src/main/scala/scalan/primitives/NumericOps.scala
+++ b/core/src/main/scala/scalan/primitives/NumericOps.scala
@@ -2,7 +2,10 @@ package scalan.primitives
 
 import scalan.{ExactNumeric, Base, Scalan, ExactIntegral}
 
+/** Slice in Scala cake with definitions of numeric operations. */
 trait NumericOps extends Base { self: Scalan =>
+
+  /** Extension methods over `Ref[T]` where T is instance of ExactNumeric type-class. */
   implicit class NumericOpsCls[T](x: Ref[T])(implicit val n: ExactNumeric[T]) {
     def +(y: Ref[T]): Ref[T] = NumericPlus(n)(x.elem).apply(x, y)
     def -(y: Ref[T]): Ref[T] = NumericMinus(n)(x.elem).apply(x, y)
@@ -15,6 +18,7 @@ trait NumericOps extends Base { self: Scalan =>
     def toLong: Ref[Long] = NumericToLong(n).apply(x)
   }
 
+  /** Extension methods over `Ref[T]` where T is instance of ExactIntegral type-class. */
   implicit class IntegralOpsCls[T](x: Ref[T])(implicit i: ExactIntegral[T]) {
     def div(y: Ref[T]): Ref[T] = IntegralDivide(i)(x.elem).apply(x, y)
     def mod(y: Ref[T]): Ref[T] = IntegralMod(i)(x.elem).apply(x, y)
@@ -23,35 +27,80 @@ trait NumericOps extends Base { self: Scalan =>
     def %(y: Ref[T]): Ref[T] = mod(y)
   }
 
+  /** Return an ExactNumeric for a given type T. */
   def numeric[T:ExactNumeric]: ExactNumeric[T] = implicitly[ExactNumeric[T]]
+
+  /** Return an ExactIntegral for a given type T. */
   def integral[T:ExactIntegral]: ExactIntegral[T] = implicitly[ExactIntegral[T]]
 
-  case class NumericPlus[T: Elem](n: ExactNumeric[T]) extends EndoBinOp[T]("+", n.plus)
+  /** Descriptor of binary `+` operation. */
+  case class NumericPlus[T: Elem](n: ExactNumeric[T]) extends EndoBinOp[T]("+") {
+    override def applySeq(x: T, y: T): T = n.plus(x, y)
+  }
 
-  case class NumericMinus[T: Elem](n: ExactNumeric[T]) extends EndoBinOp[T]("-", n.minus)
+  /** Descriptor of binary `-` operation. */
+  case class NumericMinus[T: Elem](n: ExactNumeric[T]) extends EndoBinOp[T]("-") {
+    override def applySeq(x: T, y: T): T = n.minus(x, y)
+  }
 
-  case class NumericTimes[T: Elem](n: ExactNumeric[T]) extends EndoBinOp[T]("*", n.times)
+  /** Descriptor of binary `*` operation. */
+  case class NumericTimes[T: Elem](n: ExactNumeric[T]) extends EndoBinOp[T]("*") {
+    override def applySeq(x: T, y: T): T = n.times(x, y)
+  }
 
-  class DivOp[T: Elem](opName: String, applySeq: (T, T) => T, n: ExactIntegral[T]) extends EndoBinOp[T](opName, applySeq) {
+  /** Base class for descriptors of binary division operations. */
+  abstract class DivOp[T: Elem](opName: String, n: ExactIntegral[T]) extends EndoBinOp[T](opName) {
     override def shouldPropagate(lhs: T, rhs: T) = rhs != n.zero
   }
 
-  case class NumericNegate[T: Elem](n: ExactNumeric[T]) extends UnOp[T, T]("-", n.negate)
+  /** Descriptor of unary `-` operation. */
+  case class NumericNegate[T: Elem](n: ExactNumeric[T]) extends UnOp[T, T]("-") {
+    override def applySeq(x: T): T = n.negate(x)
+  }
 
-  case class NumericToDouble[T](n: ExactNumeric[T]) extends UnOp[T,Double]("ToDouble", n.toDouble)
+  /** Descriptor of unary `ToDouble` conversion operation. */
+  case class NumericToDouble[T](n: ExactNumeric[T]) extends UnOp[T,Double]("ToDouble") {
+    override def applySeq(x: T): Double = n.toDouble(x)
+  }
 
-  case class NumericToFloat[T](n: ExactNumeric[T]) extends UnOp[T, Float]("ToFloat", n.toFloat)
+  /** Descriptor of unary `ToFloat` conversion operation. */
+  case class NumericToFloat[T](n: ExactNumeric[T]) extends UnOp[T, Float]("ToFloat") {
+    override def applySeq(x: T): Float = n.toFloat(x)
+  }
 
-  case class NumericToInt[T](n: ExactNumeric[T]) extends UnOp[T,Int]("ToInt", n.toInt)
+  /** Descriptor of unary `ToInt` conversion operation. */
+  case class NumericToInt[T](n: ExactNumeric[T]) extends UnOp[T,Int]("ToInt") {
+    override def applySeq(x: T): Int = n.toInt(x)
+  }
 
-  case class NumericToLong[T](n: ExactNumeric[T]) extends UnOp[T,Long]("ToLong", n.toLong)
+  /** Descriptor of unary `ToLong` conversion operation. */
+  case class NumericToLong[T](n: ExactNumeric[T]) extends UnOp[T,Long]("ToLong") {
+    override def applySeq(x: T): Long = n.toLong(x)
+  }
 
-  case class Abs[T: Elem](n: ExactNumeric[T]) extends UnOp[T, T]("Abs", n.abs)
+  /** Descriptor of unary `abs` operation. */
+  case class Abs[T: Elem](n: ExactNumeric[T]) extends UnOp[T, T]("Abs") {
+    override def applySeq(x: T): T = n.abs(x)
+  }
 
-  case class IntegralDivide[T](i: ExactIntegral[T])(implicit elem: Elem[T]) extends DivOp[T]("/", i.quot, i)
+  /** Descriptor of binary `/` operation (integral division). */
+  case class IntegralDivide[T](i: ExactIntegral[T])(implicit elem: Elem[T]) extends DivOp[T]("/", i) {
+    override def applySeq(x: T, y: T): T = i.quot(x, y)
+  }
 
-  case class IntegralMod[T](i: ExactIntegral[T])(implicit elem: Elem[T]) extends DivOp[T]("%", i.rem, i)
+  /** Descriptor of binary `%` operation (reminder of integral division). */
+case class IntegralMod[T](i: ExactIntegral[T])(implicit elem: Elem[T]) extends DivOp[T]("%", i) {
+    /** Note, this is implemented using `ExactIntegral.rem` method which delegates to
+      * `scala.math.Integral.rem`. The later also implements `%` operator in Scala for
+      * numeric types.
+      * @see sigmastate.eval.NumericOps.BigIntIsIntegral
+      */
+    override def applySeq(x: T, y: T): T = i.rem(x, y)
+  }
 
+  /** Compares the given value with zero of the given ExactNumeric instance. */
   @inline final def isZero[T](x: T, n: ExactNumeric[T]) = x == n.zero
+
+  /** Compares the given value with 1 of the given ExactNumeric instance. */
   @inline final def isOne[T](x: T, n: ExactNumeric[T]) = x == n.fromInt(1)
 }
diff --git a/core/src/main/scala/scalan/primitives/OrderingOps.scala b/core/src/main/scala/scalan/primitives/OrderingOps.scala
index 19045be96a..7d997e1487 100644
--- a/core/src/main/scala/scalan/primitives/OrderingOps.scala
+++ b/core/src/main/scala/scalan/primitives/OrderingOps.scala
@@ -2,10 +2,12 @@ package scalan.primitives
 
 import scalan.{Base, Scalan, ExactOrdering}
 
+/** Slice in Scala cake with definitions of comparison operations. */
 trait OrderingOps extends Base { self: Scalan =>
   implicit def repOrderingToOrderingOps[T](x: Ref[T])(implicit n: ExactOrdering[T]) = new OrderingOpsCls(x)
   implicit def OrderingToOrderingOps[T](x: T)(implicit n: ExactOrdering[T], et: Elem[T]) = new OrderingOpsCls(toRep(x))
 
+  /** Extension method over `Ref[T]` given an instance of ExactOrdering for T. */
   class OrderingOpsCls[T](lhs: Ref[T])(implicit val n: ExactOrdering[T]) {
     def <(rhs: Ref[T]) = OrderingLT(n).apply(lhs,rhs)
     def <=(rhs: Ref[T]) = OrderingLTEQ(n).apply(lhs,rhs)
@@ -16,17 +18,38 @@ trait OrderingOps extends Base { self: Scalan =>
     def compare(rhs: Ref[T]): Ref[Int] = OrderingCompare(n).apply(lhs,rhs)
   }
 
-  case class OrderingLT[T](ord: ExactOrdering[T]) extends BinOp[T, Boolean]("<", ord.lt)
+  /** Descriptor of binary `<` operation. */
+  case class OrderingLT[T](ord: ExactOrdering[T]) extends BinOp[T, Boolean]("<") {
+    override def applySeq(x: T, y: T): Boolean = ord.lt(x, y)
+  }
 
-  case class OrderingLTEQ[T](ord: ExactOrdering[T]) extends BinOp[T, Boolean]("<=", ord.lteq)
+  /** Descriptor of binary `<=` operation. */
+  case class OrderingLTEQ[T](ord: ExactOrdering[T]) extends BinOp[T, Boolean]("<=") {
+    override def applySeq(x: T, y: T): Boolean = ord.lteq(x, y)
+  }
 
-  case class OrderingGT[T](ord: ExactOrdering[T]) extends BinOp[T, Boolean](">", ord.gt)
+  /** Descriptor of binary `>` operation. */
+  case class OrderingGT[T](ord: ExactOrdering[T]) extends BinOp[T, Boolean](">") {
+    override def applySeq(x: T, y: T): Boolean = ord.gt(x, y)
+  }
 
-  case class OrderingGTEQ[T](ord: ExactOrdering[T]) extends BinOp[T, Boolean](">=", ord.gteq)
+  /** Descriptor of binary `>=` operation. */
+  case class OrderingGTEQ[T](ord: ExactOrdering[T]) extends BinOp[T, Boolean](">=") {
+    override def applySeq(x: T, y: T): Boolean = ord.gteq(x, y)
+  }
 
-  case class OrderingMax[T: Elem](ord: ExactOrdering[T]) extends BinOp[T, T]("max", ord.max)
+  /** Descriptor of binary `max` operation. */
+  case class OrderingMax[T: Elem](ord: ExactOrdering[T]) extends BinOp[T, T]("max") {
+    override def applySeq(x: T, y: T): T = ord.max(x, y)
+  }
 
-  case class OrderingMin[T: Elem](ord: ExactOrdering[T]) extends BinOp[T, T]("min", ord.min)
+  /** Descriptor of binary `min` operation. */
+  case class OrderingMin[T: Elem](ord: ExactOrdering[T]) extends BinOp[T, T]("min") {
+    override def applySeq(x: T, y: T): T = ord.min(x, y)
+  }
 
-  case class OrderingCompare[T](ord: ExactOrdering[T]) extends BinOp[T, Int]("compare", ord.compare)
+  /** Descriptor of binary `compare` operation. */
+  case class OrderingCompare[T](ord: ExactOrdering[T]) extends BinOp[T, Int]("compare") {
+    override def applySeq(x: T, y: T): Int = ord.compare(x, y)
+  }
 }
\ No newline at end of file
diff --git a/core/src/main/scala/scalan/primitives/Thunks.scala b/core/src/main/scala/scalan/primitives/Thunks.scala
index 739285f648..323fd26042 100644
--- a/core/src/main/scala/scalan/primitives/Thunks.scala
+++ b/core/src/main/scala/scalan/primitives/Thunks.scala
@@ -10,50 +10,85 @@ import scalan.util.{Covariant, GraphUtil}
 
 import scala.collection.Seq
 
+/** Slice in the [[Scalan]] cake with definitions of Thunk operations.
+  * See https://en.wikipedia.org/wiki/Thunk.
+  * Thunks are used to represent lazy operations in the graph IR.
+  * @see ApplyBinOpLazy, IfThenElseLazy
+  */
 trait Thunks extends Functions with GraphVizExport { self: Scalan =>
 
   type Th[+T] = Ref[Thunk[T]]
+
+  /** Phantom type to define thunk-typed graph nodes and thunk based lazy operations.
+    * Usually used inside [[Ref]], see for example [[Th]].
+    * See also for details http://gigiigig.github.io/tlp-step-by-step/phantom-types.html
+    */
   trait Thunk[+A] { def value: A }
+
+  /** A class of factory to create new Thunks by use `Thunk { ... }` expressions. */
   class ThunkCompanion {
     def apply[T](block: => Ref[T]) = thunk_create(block)
     def forced[T](block: => Ref[T]) = thunk_create(block).force
   }
+
+  /** Allow expressions like `Thunk { ... }` to create new Thunks. */
   val Thunk: ThunkCompanion = new ThunkCompanion
 
+  /** Extension methods on `Ref[Thunk[T]]` values. */
   implicit class RepThunkOps[T](t: Th[T]) {
+    /** Forces evaluation of the thunk to produce the delayed value. */
     def force() = thunk_force(t)
+
+    /** Creates a new thunk which, when forced, in turn forces `t` and then maps the resulting
+      * value using `f`. The application of `f` may be inlined to the new thunk body, or
+      * may be reified as [[Apply]] node, this depends on parameters of Lambda node.
+      *
+      * @param f reference to graph node of type [[Lambda]]
+      */
     def map[R](f: Ref[T => R]): Th[R] = thunk_map(t, f)
+
+    /** Creates a new thunk which, when forced, in turn forces `t` and then maps the resulting
+      * value using `f`.
+      * @param f scala function which is always inlined (staged) into the new think body
+      */
     def map[R](f: Ref[T] => Ref[R]): Th[R] = thunk_map1(t, f)
   }
 
+  /** Thunk is an instance of container type class [[Cont]]. */
   implicit val thunkCont: Cont[Thunk] = new Cont[Thunk] {
-    def lift[T](implicit eT: Elem[T]) = element[Thunk[T]]
-    def unlift[T](implicit eFT: Elem[Thunk[T]]) = eFT.eItem
-    def unapply[T](e: Elem[_]) = e match {
+    override def lift[T](implicit eT: Elem[T]) = element[Thunk[T]]
+    override def unlift[T](implicit eFT: Elem[Thunk[T]]) = eFT.eItem
+    override def unapply[T](e: Elem[_]) = e match {
       case e: ThunkElem[_] => Some(asElem[Thunk[T]](e))
       case _ => None
     }
   }
 
   import Liftables._
-  import scala.reflect.{ClassTag, classTag}
+
+  /** Runtime representation of lazy values.
+    * Each [[Thunk]] typed graph node evaluates to a value of this type.
+    */
   type SThunk[T] = () => T
 
+  /** Graph node to represent constants of type [[Thunk]].
+    * @see scalan.Base.Liftables.Liftable */
   case class ThunkConst[ST, T](constValue: SThunk[ST], lT: Liftable[ST, T])
       extends BaseDef[Thunk[T]]()(thunkElement(lT.eW))
          with LiftedConst[SThunk[ST], Thunk[T]] {
     val liftable: Liftable[SThunk[ST], Thunk[T]] = liftableThunk(lT)
   }
 
+  /** Implementation of Liftable type class for `Thunk[T]` given liftable for `T`. */
   case class LiftableThunk[ST, T](lT: Liftable[ST, T]) extends Liftable[SThunk[ST], Thunk[T]] {
     import RType._
-    def eW: Elem[Thunk[T]] = thunkElement(lT.eW)
-    def sourceType: RType[SThunk[ST]] = {
+    override def eW: Elem[Thunk[T]] = thunkElement(lT.eW)
+    override def sourceType: RType[SThunk[ST]] = {
       implicit val tST = lT.sourceType
       RType[SThunk[ST]]
     }
-    def lift(x: SThunk[ST]): Ref[Thunk[T]] = ThunkConst(x, lT)
-    def unlift(w: Ref[Thunk[T]]): SThunk[ST] = w.node match {
+    override def lift(x: SThunk[ST]): Ref[Thunk[T]] = ThunkConst(x, lT)
+    override def unlift(w: Ref[Thunk[T]]): SThunk[ST] = w.node match {
       case ThunkConst(x: SThunk[_], l) if l == lT => x.asInstanceOf[SThunk[ST]]
       case _ => unliftError(w)
     }
@@ -63,6 +98,7 @@ trait Thunks extends Functions with GraphVizExport { self: Scalan =>
     LiftableThunk(lT)
 
 
+  /** Implements a type descriptor of `Thunk[A]` type given the instance of `A`. */
   case class ThunkElem[A](override val eItem: Elem[A])
     extends EntityElem1[A, Thunk[A], Thunk](eItem, container[Thunk]) {
     override lazy val liftable = asLiftable[SThunk[_], Thunk[A]](liftableThunk(eItem.liftable))
@@ -71,14 +107,24 @@ trait Thunks extends Functions with GraphVizExport { self: Scalan =>
 
   implicit def thunkElement[T](implicit eItem: Elem[T]): Elem[Thunk[T]] =
     cachedElemByClass(eItem)(classOf[ThunkElem[T]])
+
+  /** Implicit conversion (downcast) to access `ThunkElem.eItem` field. */
   implicit def extendThunkElement[T](elem: Elem[Thunk[T]]): ThunkElem[T] = elem.asInstanceOf[ThunkElem[T]]
 
-  class ThunkDef[A](val root: Ref[A], _scheduleIds: =>ScheduleIds)
+  /** Graph node representing thunk with reified body.
+    * Each thunk node is a specialized implementation of AstGraph abstract class.
+    * @param _scheduleIds compact representation of thunk body, i.e. a sequence of graph
+    *                     nodes, which will be executed when the thunk is forced. Each
+    *                     node is given by its id. The node can be resolved using
+    *                     `getSym(id).node` expression.
+    * @param root graph node, which represents the result value of thunk forcing.
+    */
+  class ThunkDef[A](val root: Ref[A], _scheduleIds: => ScheduleIds)
     extends AstGraph with Def[Thunk[A]] {
 
     implicit def eA: Elem[A] = root.elem
     private var _selfType: Elem[Thunk[A]] = _
-    def resultType: Elem[Thunk[A]] =
+    override def resultType: Elem[Thunk[A]] =
       if (_selfType != null) _selfType
       else {
         val res = thunkElement(eA)
@@ -94,7 +140,7 @@ trait Thunks extends Functions with GraphVizExport { self: Scalan =>
       * different nodeIds and hence they are NOT equal.
       * */
     override lazy val hashCode: Int = _nodeId //41 * (41 + root.hashCode) + schedule.hashCode
-    def canEqual(other: Any) = other.isInstanceOf[ThunkDef[_]]
+    override def canEqual(other: Any) = other.isInstanceOf[ThunkDef[_]]
     override def equals(other: Any) =
       other match {
         case that: ThunkDef[_] => _nodeId == that._nodeId
@@ -104,18 +150,20 @@ trait Thunks extends Functions with GraphVizExport { self: Scalan =>
 
 
     // Product implementation
-    def productElement(n: Int): Any = n match {
+    override def productElement(n: Int): Any = n match {
       case 0 => root
       case _ => throw new NoSuchElementException(s"ThunkDef.productElement($n) is undefined")
     }
-    def productArity: Int = 1
+    override def productArity: Int = 1
+
+    override def boundVars = EmptySeqOfSym
 
-    override def boundVars = Nil
-    override lazy val freeVars: Seq[Sym] = if (schedule.isEmpty) Array(root) else super.freeVars
+    override val roots: Seq[Sym] = Array(root)
+
+    override lazy val freeVars: Seq[Sym] = if (schedule.isEmpty) roots else super.freeVars
 
     override protected def getDeps: Array[Sym] = freeVars.toArray
 
-    val roots: Seq[Sym] = Array(root)
     override lazy val rootIds: DBuffer[Int] = super.rootIds
     override def isIdentity: Boolean = false
   }
@@ -126,18 +174,27 @@ trait Thunks extends Functions with GraphVizExport { self: Scalan =>
     }
   }
 
+  /** Helper object to handle construction of nested thunks. One instance is created for
+    * each ThunkDef under construction. This corresponds to syntactic nesting of thunks.
+    * @param parent  the scope of the parent thunk
+    * @param thunkSym reference to the Graph node for which this scope is created.
+    */
   class ThunkScope(val parent: ThunkScope, val thunkSym: Ref[Any]) {
     private val bodyIds: DSet[Int] = DSet.ofSize(16)
     private val bodyDefs: AVHashMap[Def[_], Def[_]] = AVHashMap(32)
 
     @inline final def isEmptyBody: Boolean = bodyIds.isEmpty
 
+    /** Add the given graph node (by symbol) to this scope. */
     def +=(sym: Sym): Unit = {
       val d = sym.node
       bodyIds += d.nodeId
       bodyDefs.put(d, d)
     }
 
+    /** Sort graph nodes of this scope topologically using depth-first search along
+      * node dependencies (graph edges). This will give evaluation order of the thunk.
+      */
     def scheduleForResult(root: Ref[Any]): DBuffer[Int] = {
       val sch = GraphUtil.depthFirstOrderFrom(
         DBuffer(root.node.nodeId),
@@ -156,6 +213,11 @@ trait Thunks extends Functions with GraphVizExport { self: Scalan =>
       sch
     }
 
+    /** Find the given node among definitions accessible from this scope.
+      * It searches in the chain of nested scopes for the first match.
+      * If not found, searches in the global scope.
+      * @return null if not found at all.
+      */
     def findDef[T](d: Def[T]): Ref[T] = {
       val existingOpt = bodyDefs.get(d)
       if (existingOpt.isDefined) return existingOpt.get.self.asInstanceOf[Ref[T]]
@@ -166,27 +228,49 @@ trait Thunks extends Functions with GraphVizExport { self: Scalan =>
     }
   }
 
+  /** The stack of nested thunks during graph construction. */
   class ThunkStack {
+    /** Stack is represented as simple list with th first element as a top of the stack. */
     var stack = List[ThunkScope]()
+
+    /** @return optional top scope. */
     @inline def top: Nullable[ThunkScope] = if (stack.isEmpty) Nullable.None else Nullable(stack.head)
+
+    /** Push new scope when start constructing new thunk. */
     def push(e: ThunkScope): this.type = { stack = e :: stack; this }
+
+    /** Pop new scope when thunk has been constructed. */
     @inline def pop: ThunkScope = {
       val res = stack.head
       stack = stack.tail
       res
     }
+
+    /** For a given thunk node, create a new scope and push it on the stack. */
     def beginScope(thunkSym: Ref[Any]): ThunkScope = {
       val parent = if (stack.isEmpty) null else stack.head
       val scope = new ThunkScope(parent, thunkSym)
       this.push(scope)
       scope
     }
+
+    /** End current scope and pop it from the stack. */
     @inline def endScope(): Unit = { this.pop }
   }
+
   protected val thunkStack = new ThunkStack
 
   implicit def repToThunk[A](block: Ref[A]): Ref[Thunk[A]] = thunk_create(block)
 
+  /** Constructs a new thunk node by executing the given `block` and collecting all the
+    * graph node created along the way.
+    * This methods:
+    * 1) starts a new nested ThunkScope,
+    * 2) executes the `block` to obtain resulting graph node
+    * 3) schedule thunk body for execution order
+    * 4) adds a new ThunkDef node and returns its reference.
+    * @return a reference to the newly created [[ThunkDef]] node
+    */
   def thunk_create[A](block: => Ref[A]): Ref[Thunk[A]] = {
     var scheduleIds: ScheduleIds = null
     val resPH = placeholder(Lazy(AnyElement)).asInstanceOf[Ref[A]] // will be known after block is evaluated
@@ -219,18 +303,38 @@ trait Thunks extends Functions with GraphVizExport { self: Scalan =>
     }
   }
 
+  /** Specifies thunk staging strategy with respect to handling thunk_force operation.
+    * @see thunk_force
+    */
   var isInlineThunksOnForce = false
 
+  /** Inlines the given thunk by cloning all its nodes and applying the given substitution (transformer).
+    * @param thunk reference to the thunk node
+    * @param subst transformer to be applied for each mirrored (cloned) node.
+    * @return the reference to the graph node, which represents the resulting value of the thunk
+    */
   def forceThunkByMirror[A](thunk: Th[A], subst: MapTransformer = MapTransformer.empty()): Ref[A] = {
     val th = thunk.node.asInstanceOf[ThunkDef[A]]
     forceThunkDefByMirror(th, subst)
   }
+
+  /** Inlines the given thunk by cloning all its nodes and applying the given substitution (transformer).
+    * @param th the thunk node
+    * @param subst transformer to be applied for each mirrored (cloned) node.
+    * @return the reference to the graph node, which represents the resulting value of the thunk
+    */
   def forceThunkDefByMirror[A](th: ThunkDef[A], subst: MapTransformer = MapTransformer.empty()): Ref[A] = {
     val body = th.scheduleIds
     val t = DefaultMirror.mirrorSymbols(subst, NoRewriting, th, body)
     t(th.root)
   }
 
+  /** Logical force of the thunk. Depending on isInlineThunksOnForce it either inlines the
+    * thunk body or creates a new ThunkForce node.
+    *
+    * @return a reference to the graph node, which represent the result of the thunk's
+    *         evaluation.
+    */
   def thunk_force[A](t: Th[A]): Ref[A] =
     if (isInlineThunksOnForce)
       t.node match {
@@ -241,6 +345,7 @@ trait Thunks extends Functions with GraphVizExport { self: Scalan =>
     else
       ThunkForce(t)
 
+  /** Graph node to represent thunk forcing operation. */
   case class ThunkForce[A](thunk: Ref[Thunk[A]]) extends Def[A] {
     implicit def resultType = thunk.elem.eItem
     override def transform(t: Transformer) = ThunkForce(t(thunk))
diff --git a/core/src/main/scala/scalan/primitives/UnBinOps.scala b/core/src/main/scala/scalan/primitives/UnBinOps.scala
index ed690e7aa6..749556bf0e 100644
--- a/core/src/main/scala/scalan/primitives/UnBinOps.scala
+++ b/core/src/main/scala/scalan/primitives/UnBinOps.scala
@@ -4,44 +4,75 @@ import scalan.{Scalan, Base}
 
 trait UnBinOps extends Base { self: Scalan =>
 
-  class UnOp[A, R](val opName: String, val applySeq: A => R)(implicit val eResult: Elem[R]) {
+  /** Base class for descriptors of unary operations. */
+  abstract class UnOp[A, R](val opName: String)(implicit val eResult: Elem[R]) {
     override def toString = opName
+    /** Called as part of graph interpretation to execute the given unary operation.
+      * @param x operation argument
+      * @return result of applying this operation to x
+      */
+    def applySeq(x: A): R
 
+    /** Builds a new graph node by applying this operation to the given argument. */
     def apply(arg: Ref[A]) = applyUnOp(this, arg)
 
+    /** Whether the constants should be propagated through this operations by rewriting. */
     def shouldPropagate(arg: A) = true
   }
 
-  class BinOp[A, R](val opName: String, val applySeq: (A, A) => R)(implicit val eResult: Elem[R]) {
+  /** Base class for descriptors of binary operations. */
+  abstract class BinOp[A, R](val opName: String)(implicit val eResult: Elem[R]) {
     override def toString = opName
 
+    /** Called as part of graph interpretation to execute the given binary operation.
+      * @param x operation argument
+      * @param y operation argument
+      * @return result of applying this operation to (x, y)
+      */
+    def applySeq(x: A, y: A): R
+
+    /** Builds a new graph node by applying this operation to the given arguments. */
     def apply(lhs: Ref[A], rhs: Ref[A]) = applyBinOp(this, lhs, rhs)
+
+    /** Builds a new graph node by applying this operation to the given arguments.
+      * This is a short-cuting (aka lazy) version of the operation, where the lazyness is
+      * represented by Thunk.
+      */
     def applyLazy(lhs: Ref[A], rhs: Ref[Thunk[A]]) = applyBinOpLazy(this, lhs, rhs)
 
-    // ideally shouldn't be necessary, but
-    // we curently can't handle division by zero properly
+    /** Whether the constants should be propagated through this operations by rewriting. */
     def shouldPropagate(lhs: A, rhs: A) = true
   }
 
   type EndoUnOp[A] = UnOp[A, A]
   type EndoBinOp[A] = BinOp[A, A]
 
+  /** Graph node which represents application of the given unary operation to the given argument. */
   case class ApplyUnOp[A, R](op: UnOp[A, R], arg: Ref[A]) extends BaseDef[R]()(op.eResult) {
     override def toString = s"$op($arg)"
     override def transform(t: Transformer): Def[R] = ApplyUnOp[A,R](op, t(arg))
   }
 
+  /** Graph node which represents application of the given binary operation to the given arguments. */
   case class ApplyBinOp[A, R](op: BinOp[A, R], lhs: Ref[A], rhs: Ref[A]) extends BaseDef[R]()(op.eResult) {
     override def toString = s"$op($lhs, $rhs)"
     override def transform(t: Transformer): Def[R] = ApplyBinOp[A,R](op, t(lhs), t(rhs))
   }
+
+  /** Graph node which represents application of the given binary operation to the given arguments
+    * where the second argument is lazy.
+    */
   case class ApplyBinOpLazy[A, R](op: BinOp[A, R], lhs: Ref[A], rhs: Ref[Thunk[A]]) extends BaseDef[R]()(op.eResult) {
     override def toString = s"$lhs $op { $rhs }"
     override def transform(t: Transformer): Def[R] = ApplyBinOpLazy[A,R](op, t(lhs), t(rhs))
   }
 
+  /** Overridable constructor of an unary operation node. */
   def applyUnOp[A, R](op: UnOp[A, R], arg: Ref[A]): Ref[R] = ApplyUnOp(op, arg)
 
+  /** Overridable constructor of a binary operation node. */
   def applyBinOp[A, R](op: BinOp[A, R], lhs: Ref[A], rhs: Ref[A]): Ref[R] = ApplyBinOp(op, lhs, rhs)
+
+  /** Overridable constructor of a binary operation node with lazy argument. */
   def applyBinOpLazy[A, R](op: BinOp[A, R], lhs: Ref[A], rhs: Ref[Thunk[A]]): Ref[R] = ApplyBinOpLazy(op, lhs, rhs)
 }
\ No newline at end of file
diff --git a/core/src/main/scala/scalan/primitives/UniversalOps.scala b/core/src/main/scala/scalan/primitives/UniversalOps.scala
index 30aeb28dae..eaca5821ce 100644
--- a/core/src/main/scala/scalan/primitives/UniversalOps.scala
+++ b/core/src/main/scala/scalan/primitives/UniversalOps.scala
@@ -3,9 +3,13 @@ package scalan.primitives
 import scalan.{Base, Scalan}
 
 trait UniversalOps extends Base { scalan: Scalan =>
-  case class HashCode[A]() extends UnOp[A, Int]("hashCode", _.hashCode)
+  case class HashCode[A]() extends UnOp[A, Int]("hashCode") {
+    override def applySeq(x: A): Int = x.hashCode
+  }
 
-  case class ToString[A]() extends UnOp[A, String]("toString", _.toString)
+  case class ToString[A]() extends UnOp[A, String]("toString") {
+    override def applySeq(x: A): String = x.toString
+  }
 
   /** Represents calculation of size in bytes of the given value.
     * The descriptor value.elem can be used to decompose value into components.
diff --git a/core/src/main/scala/scalan/staged/AstGraphs.scala b/core/src/main/scala/scalan/staged/AstGraphs.scala
index a9967bf100..dd801e25e3 100644
--- a/core/src/main/scala/scalan/staged/AstGraphs.scala
+++ b/core/src/main/scala/scalan/staged/AstGraphs.scala
@@ -1,7 +1,7 @@
 package scalan.staged
 
 import scala.collection._
-import scalan.Scalan
+import scalan.{Base, Scalan, emptyDBufferOfInt}
 import scalan.compilation.GraphVizConfig
 import spire.syntax.all.cfor
 import debox.{Set => DSet, Buffer => DBuffer, Map => DMap}
@@ -70,11 +70,16 @@ trait AstGraphs extends Transforming { self: Scalan =>
           }
         }
       }
-      val res = new Array[Sym](resIds.length)
-      cfor(0)(_ < resIds.length, _ + 1) { i =>
-        res(i) = getSym(resIds(i))
+      val resLength = resIds.length
+      if (resLength == 0)
+        EmptySeqOfSym
+      else {
+        val res = new Array[Sym](resLength)
+        cfor(0)(_ < resLength, _ + 1) { i =>
+          res(i) = getSym(resIds(i))
+        }
+        res
       }
-      res
     }
 
     /** Schedule represents a body of compound definition - topologically ordered
@@ -86,21 +91,31 @@ trait AstGraphs extends Transforming { self: Scalan =>
     /** Sequence of node references forming a schedule.
       * @hotspot don't beautify the code */
     lazy val schedule: Schedule = {
-      val len = scheduleIds.length
-      val res = new Array[Sym](len)
-      cfor(0)(_ < len, _ + 1) { i =>
-        res(i) = getSym(scheduleIds(i))
+      val ids = scheduleIds
+      val len = ids.length
+      if (len == 0) EmptySeqOfSym
+      else {
+        val res = new Array[Sym](len)
+        cfor(0)(_ < len, _ + 1) { i =>
+          res(i) = getSym(ids(i))
+        }
+        res
       }
-      res
     }
 
     /** Set of symbol ids in the schedule. Can be used to quickly recognize
       * symbols belonging to the body of this definition.
       */
     lazy val domain: DSet[Int] = {
-      val res = DSet.ofSize[Int](scheduleIds.length)
-      res ++= scheduleIds.toArray
-      res
+      val ids = scheduleIds
+      val len = ids.length
+      if (len == 0) {
+        EmptyDSetOfInt
+      } else {
+        val res = DSet.ofSize[Int](len)
+        res ++= ids.toArray
+        res
+      }
     }
 
     /** Whether this graph represents identity function. */
@@ -132,7 +147,10 @@ trait AstGraphs extends Transforming { self: Scalan =>
     lazy val flatSchedule: Schedule = {
       val flatBuf = DBuffer.ofSize[Sym](schedule.length)
       buildFlatSchedule(schedule, flatBuf)
-      flatBuf.toArray
+      if (flatBuf.length > 0)
+        flatBuf.toArray
+      else
+        EmptySeqOfSym
     }
 
     /** Build usage information induced by the given schedule.
@@ -180,21 +198,15 @@ trait AstGraphs extends Transforming { self: Scalan =>
 
     def globalUsagesOf(s: Sym): DBuffer[Sym] = allNodes.get(s.node.nodeId) match {
       case Some(node) => node.outSyms
-      case None => DBuffer.empty[Sym]
+      case None => emptyDBufferOfSym
     }
 
     def hasManyUsagesGlobal(s: Sym): Boolean = globalUsagesOf(s).length > 1
 
-    /** This empty buffer is returned every time the usages are requested for the node
-      * that is not in usageMap.
-      * WARNING! Since it is mutable, special care should be taken to not change this buffer.
-      * @hotspot used havily in scheduling */
-    private val NoUsages = DBuffer.unsafe(new Array[Int](0))
-
     /** @hotspot  for performance we return mutable structure, but it should never be changed. */
     def usagesOf(id: Int): DBuffer[Int] = {
       val node = usageMap.getOrElse(id, null)
-      if (node == null) return NoUsages
+      if (node == null) return emptyDBufferOfInt
       node.usages
     }
 
diff --git a/sigma-impl/src/main/scala/special/sigma/TestBigInt.scala b/sigma-impl/src/main/scala/special/sigma/TestBigInt.scala
index b23cea1e81..423386051b 100644
--- a/sigma-impl/src/main/scala/special/sigma/TestBigInt.scala
+++ b/sigma-impl/src/main/scala/special/sigma/TestBigInt.scala
@@ -4,8 +4,9 @@ import special.collection.Coll
 import java.math.BigInteger
 import scalan.util.Extensions.BigIntegerOps
 
+// TODO refactor: this class should be removed before v5.0
 abstract class TestBigInt(private[sigma] val value: BigInteger) extends BigInt {
-  val dsl: TestSigmaDslBuilder = new TestSigmaDslBuilder
+  def dsl: TestSigmaDslBuilder
 
   override def toByte : Byte  = value.byteValueExact()
   override def toShort: Short = value.shortValueExact()
diff --git a/sigma-impl/src/main/scala/special/sigma/TestGroupElement.scala b/sigma-impl/src/main/scala/special/sigma/TestGroupElement.scala
index bf57777773..d8b84fd2f2 100644
--- a/sigma-impl/src/main/scala/special/sigma/TestGroupElement.scala
+++ b/sigma-impl/src/main/scala/special/sigma/TestGroupElement.scala
@@ -3,8 +3,9 @@ package special.sigma
 import org.bouncycastle.math.ec.ECPoint
 import special.collection.Coll
 
+// TODO refactor: this class should be removed before v5.0
 abstract class TestGroupElement(private[sigma] val value: ECPoint) extends GroupElement {
-  val dsl: TestSigmaDslBuilder = new TestSigmaDslBuilder
+  def dsl: TestSigmaDslBuilder
 
   override def toString: String = s"GroupElement(${Extensions.showECPoint(value)})"
 
diff --git a/sigmastate/src/main/scala/org/ergoplatform/ErgoAddress.scala b/sigmastate/src/main/scala/org/ergoplatform/ErgoAddress.scala
index 6adc685cc6..1116b9fbf4 100644
--- a/sigmastate/src/main/scala/org/ergoplatform/ErgoAddress.scala
+++ b/sigmastate/src/main/scala/org/ergoplatform/ErgoAddress.scala
@@ -262,7 +262,7 @@ case class ErgoAddressEncoder(networkPrefix: NetworkPrefix) {
   import ErgoAddressEncoder._
 
   /** This value is be used implicitly in the methods below. */
-  implicit private val ergoAddressEncoder: ErgoAddressEncoder = this
+  implicit private def ergoAddressEncoder: ErgoAddressEncoder = this
 
   /** Converts the given [[ErgoAddress]] to Base58 string. */
   def toString(address: ErgoAddress): String = {
diff --git a/sigmastate/src/main/scala/org/ergoplatform/ErgoLikeContext.scala b/sigmastate/src/main/scala/org/ergoplatform/ErgoLikeContext.scala
index 438978fd34..6f5544e847 100644
--- a/sigmastate/src/main/scala/org/ergoplatform/ErgoLikeContext.scala
+++ b/sigmastate/src/main/scala/org/ergoplatform/ErgoLikeContext.scala
@@ -118,17 +118,16 @@ class ErgoLikeContext(val lastBlockUtxoRoot: AvlTreeData,
       dataBoxes, boxesToSpend, newSpendingTransaction, selfIndex, extension, validationSettings, costLimit, initCost)
 
 
-  override def toSigmaContext(IR: Evaluation, isCost: Boolean, extensions: Map[Byte, AnyValue] = Map()): sigma.Context = {
-    implicit val IRForBox: Evaluation = IR
+  override def toSigmaContext(isCost: Boolean, extensions: Map[Byte, AnyValue] = Map()): sigma.Context = {
     import Evaluation._
 
-    def contextVars(m: Map[Byte, AnyValue])(implicit IR: Evaluation): Coll[AnyValue] = {
+    def contextVars(m: Map[Byte, AnyValue]): Coll[AnyValue] = {
       val maxKey = if (m.keys.isEmpty) 0 else m.keys.max
       val res = new Array[AnyValue](maxKey + 1)
       for ((id, v) <- m) {
         res(id) = v
       }
-      IR.sigmaDslBuilderValue.Colls.fromArray(res)
+      CostingSigmaDslBuilder.Colls.fromArray(res)
     }
 
     val dataInputs = this.dataBoxes.toArray.map(_.toTestBox(isCost)).toColl
diff --git a/sigmastate/src/main/scala/sigmastate/Values.scala b/sigmastate/src/main/scala/sigmastate/Values.scala
index cb029de642..b2a0409761 100644
--- a/sigmastate/src/main/scala/sigmastate/Values.scala
+++ b/sigmastate/src/main/scala/sigmastate/Values.scala
@@ -37,6 +37,7 @@ import sigmastate.lang.SourceContext
 import special.collection.Coll
 
 import scala.collection.mutable
+import scala.collection.mutable.ArrayBuffer
 
 object Values {
 
@@ -114,6 +115,12 @@ object Values {
     }
     def notSupportedError(v: SValue, opName: String) =
       throw new IllegalArgumentException(s"Method $opName is not supported for node $v")
+
+    /** Immutable empty array of values. Can be used to avoid allocation. */
+    val EmptyArray = Array.empty[SValue]
+
+    /** Immutable empty Seq of values. Can be used to avoid allocation. */
+    val EmptySeq: IndexedSeq[SValue] = EmptyArray
   }
 
   trait ValueCompanion extends SigmaNodeCompanion {
@@ -183,7 +190,17 @@ object Values {
 
   object Constant extends ValueCompanion {
     override def opCode: OpCode = ConstantCode
+
+    /** Immutable empty array, can be used to save allocations in many places. */
+    val EmptyArray = Array.empty[Constant[SType]]
+
+    /** Immutable empty IndexedSeq, can be used to save allocations in many places. */
+    val EmptySeq: IndexedSeq[Constant[SType]] = Array.empty[Constant[SType]]
+
+    /** Helper factory method. */
     def apply[S <: SType](value: S#WrappedType, tpe: S): Constant[S] = ConstantNode(value, tpe)
+
+    /** Recognizer of Constant tree nodes used in patterns. */
     def unapply[S <: SType](v: EvaluatedValue[S]): Option[(S#WrappedType, S)] = v match {
       case ConstantNode(value, tpe) => Some((value, tpe))
       case _ => None
@@ -672,8 +689,12 @@ object Values {
 //      NOTE, the assert below should be commented before production release.
 //      Is it there for debuging only, basically to catch call stacks where the fancy types may
 //      occasionally be used.
-//    assert(items.isInstanceOf[mutable.WrappedArray[_]] || items.isInstanceOf[mutable.IndexedSeq[_]],
+//    assert(
+//      items.isInstanceOf[mutable.WrappedArray[_]] ||
+//      items.isInstanceOf[ArrayBuffer[_]] ||
+//      items.isInstanceOf[mutable.ArraySeq[_]],
 //      s"Invalid types of items ${items.getClass}")
+
     private val isBooleanConstants = elementType == SBoolean && items.forall(_.isInstanceOf[Constant[_]])
     override def companion =
       if (isBooleanConstants) ConcreteCollectionBooleanConstant
@@ -751,6 +772,13 @@ object Values {
     def rhs: SValue
     def isValDef: Boolean
   }
+  object BlockItem {
+    /** Immutable empty array, can be used to save allocations in many places. */
+    val EmptyArray = Array.empty[BlockItem]
+
+    /** Immutable empty IndexedSeq to save allocations in many places. */
+    val EmptySeq: IndexedSeq[BlockItem] = EmptyArray
+  }
 
   /** IR node for let-bound expressions `let x = rhs` which is ValDef, or `let f[T] = rhs` which is FunDef.
     * These nodes are used to represent ErgoTrees after common sub-expression elimination.
@@ -810,7 +838,14 @@ object Values {
     */
   case class FuncValue(args: IndexedSeq[(Int,SType)], body: Value[SType]) extends NotReadyValue[SFunc] {
     override def companion = FuncValue
-    lazy val tpe: SFunc = SFunc(args.toArray.map(_._2), body.tpe)
+    lazy val tpe: SFunc = {
+      val nArgs = args.length
+      val argTypes = new Array[SType](nArgs)
+      cfor(0)(_ < nArgs, _ + 1) { i =>
+        argTypes(i) = args(i)._2
+      }
+      SFunc(argTypes, body.tpe)
+    }
     /** This is not used as operation, but rather to form a program structure */
     override def opType: SFunc = SFunc(mutable.WrappedArray.empty, tpe)
   }
diff --git a/sigmastate/src/main/scala/sigmastate/eval/BigIntegerOps.scala b/sigmastate/src/main/scala/sigmastate/eval/BigIntegerOps.scala
index 547092bad6..799382cf10 100644
--- a/sigmastate/src/main/scala/sigmastate/eval/BigIntegerOps.scala
+++ b/sigmastate/src/main/scala/sigmastate/eval/BigIntegerOps.scala
@@ -53,6 +53,17 @@ object NumericOps {
     def toFloat(x: BigInt): Float = CostingSigmaDslBuilder.toBigInteger(x).floatValue()
     def toDouble(x: BigInt): Double = CostingSigmaDslBuilder.toBigInteger(x).doubleValue()
   }
+
+  /** The instance of Integral for BigInt.
+    *
+    * Note: ExactIntegral is not defined for [[special.sigma.BigInt]].
+    * This is because arithmetic BigInt operations are handled specially
+    * (see `case op: ArithOp[t] if op.tpe == SBigInt =>` in RuntimeCosting.scala).
+    * As result [[scalan.primitives.UnBinOps.ApplyBinOp]] nodes are not created for BigInt
+    * operations, and hence operation descriptors such as
+    * [[scalan.primitives.NumericOps.IntegralDivide]] and
+    * [[scalan.primitives.NumericOps.IntegralMod]] are not used for BigInt.
+    */
   implicit object BigIntIsIntegral extends BigIntIsIntegral with OrderingOps.BigIntOrdering
 
   implicit object BigIntIsExactNumeric extends ExactNumeric[BigInt] {
@@ -62,13 +73,6 @@ object NumericOps {
     override def times(x: BigInt, y: BigInt): BigInt = n.times(x, y)
   }
 
-  implicit object BigIntIsExactIntegral extends ExactIntegral[BigInt] {
-    val n = BigIntIsIntegral
-    override def plus(x: BigInt, y: BigInt): BigInt = n.plus(x, y)
-    override def minus(x: BigInt, y: BigInt): BigInt = n.minus(x, y)
-    override def times(x: BigInt, y: BigInt): BigInt = n.times(x, y)
-  }
-
   implicit object BigIntIsExactOrdering extends ExactOrderingImpl[BigInt](BigIntIsIntegral)
 }
 
diff --git a/sigmastate/src/main/scala/sigmastate/eval/Evaluation.scala b/sigmastate/src/main/scala/sigmastate/eval/Evaluation.scala
index c1a6fe3d54..0ce67b66ff 100644
--- a/sigmastate/src/main/scala/sigmastate/eval/Evaluation.scala
+++ b/sigmastate/src/main/scala/sigmastate/eval/Evaluation.scala
@@ -25,6 +25,7 @@ import special.Types._
 import scala.collection.immutable.HashSet
 import scala.collection.mutable
 import scala.collection.mutable.ArrayBuffer
+import spire.syntax.all.cfor
 
 /** This is a slice in IRContext cake which implements evaluation of graphs.
   */
@@ -81,99 +82,17 @@ trait Evaluation extends RuntimeCosting { IR: IRContext =>
   private val SPCM = WSpecialPredefCompanionMethods
   private val MBM = MonoidBuilderMethods
 
-  private val _allowedOpCodesInCosting: HashSet[OpCodeExtra] = HashSet[OpCode](
-    AppendCode,
-    ByIndexCode,
-    ConstantCode,
-    DivisionCode,
-    DowncastCode,
-    ExtractBytesWithNoRefCode,
-    ExtractRegisterAs,
-    ExtractScriptBytesCode,
-    FoldCode,
-    FuncApplyCode,
-    FuncValueCode,
-    GetVarCode,
-    InputsCode,
-    LastBlockUtxoRootHashCode,
-    MapCollectionCode,
-    FlatMapCollectionCode,
-    MaxCode,
-    MethodCallCode,
-    MinCode,
-    MinusCode,
-    ModuloCode,
-    MultiplyCode,
-    OptionGetCode,
-    OptionGetOrElseCode,
-    OptionIsDefinedCode,
-    OutputsCode,
-    PlusCode,
-    SelectFieldCode,
-    SelfCode,
-    SigmaPropBytesCode,
-    SizeOfCode,
-    SliceCode,
-    TupleCode,
-    UpcastCode
-  ).map(toExtra) ++ HashSet[OpCodeExtra](
-    OpCostCode,
-    PerKbCostOfCode,
-    CastCode,
-    IntPlusMonoidCode,
-    ThunkDefCode,
-    ThunkForceCode,
-    SCMInputsCode,
-    SCMOutputsCode,
-    SCMDataInputsCode,
-    SCMSelfBoxCode,
-    SCMLastBlockUtxoRootHashCode,
-    SCMHeadersCode,
-    SCMPreHeaderCode,
-    SCMGetVarCode,
-    SBMPropositionBytesCode,
-    SBMBytesCode,
-    SBMBytesWithoutRefCode,
-    SBMRegistersCode,
-    SBMGetRegCode,
-    SBMTokensCode,
-    SSPMPropBytesCode,
-    SAVMTValCode,
-    SAVMValueSizeCode,
-    SizeMDataSizeCode,
-    SPairLCode,
-    SPairRCode,
-    SCollMSizesCode,
-    SOptMSizeOptCode,
-    SFuncMSizeEnvCode,
-    CSizePairCtorCode,
-    CSizeFuncCtorCode,
-    CSizeOptionCtorCode,
-    CSizeCollCtorCode,
-    CSizeBoxCtorCode,
-    CSizeContextCtorCode,
-    CSizeAnyValueCtorCode,
-    CReplCollCtorCode,
-    PairOfColsCtorCode,
-    CollMSumCode,
-    CBMReplicateCode,
-    CBMFromItemsCode,
-    CostOfCode,
-    UOSizeOfCode,
-    SPCMSomeCode
-  )
-
   /** Returns a set of opCodeEx values (extended op codes) which are allowed in cost function.
     * This may include both ErgoTree codes (from OpCodes) and also additional non-ErgoTree codes
     * from OpCodesExtra.
     * Any IR graph node can be uniquely assigned to extended op code value
     * from OpCodes + OpCodesExtra combined range. (See getOpCodeEx) */
-  protected def allowedOpCodesInCosting: HashSet[OpCodeExtra] = _allowedOpCodesInCosting
+  protected def allowedOpCodesInCosting: HashSet[OpCodeExtra] = Evaluation.AllowedOpCodesInCosting
 
+  /** Checks the given opCode belong to an operation allowed in cost function. */
   def isAllowedOpCodeInCosting(opCode: OpCodeExtra): Boolean = allowedOpCodesInCosting.contains(opCode)
 
-  /** Returns extended op code assigned to the given IR graph node.
-    */
+  /** Returns extended op code assigned to the given IR graph node. */
   def getOpCodeEx(d: Def[_]): OpCodeExtra = d match {
     case _: OpCost => OpCostCode
     case _: PerKbCostOf => PerKbCostOfCode
@@ -451,8 +370,6 @@ trait Evaluation extends RuntimeCosting { IR: IRContext =>
     case _ => error(s"Cannot find value in environment for $s (dataEnv = $dataEnv)")
   }
 
-  def msgCostLimitError(cost: Long, limit: Long) = s"Estimated execution cost $cost exceeds the limit $limit"
-
   /** Incapsulate simple monotonic (add only) counter with reset. */
   class CostCounter(val initialCost: Int) {
     private var _currentCost: Int = initialCost
@@ -558,7 +475,7 @@ trait Evaluation extends RuntimeCosting { IR: IRContext =>
 //          if (cost < limit)
 //            println(s"FAIL FAST in loop: $accumulatedCost > $limit")
           // TODO cover with tests
-          throw new CostLimitException(accumulatedCost, msgCostLimitError(accumulatedCost, limit), None)
+          throw new CostLimitException(accumulatedCost, Evaluation.msgCostLimitError(accumulatedCost, limit), None)
         }
       }
 
@@ -635,11 +552,22 @@ trait Evaluation extends RuntimeCosting { IR: IRContext =>
 
           case wc: LiftedConst[_,_] => out(wc.constValue)
 
-          case _: SigmaDslBuilder | _: CollBuilder | _: CostedBuilder |
-               _: WSpecialPredefCompanion |
-               _: IntPlusMonoid | _: LongPlusMonoid |
-               MBM.intPlusMonoid(_) | MBM.longPlusMonoid(_) => // TODO no HF proof
-            out(dataEnv.getOrElse(sym, !!!(s"Cannot resolve companion instance for $sym -> ${sym.node}")))
+          case _: IntPlusMonoid | MBM.intPlusMonoid(_)  =>
+            // always return the same value since monoids are singletons
+            out(monoidBuilderValue.intPlusMonoid)
+
+          case _: LongPlusMonoid | MBM.longPlusMonoid(_) =>
+            // always return the same value since monoids are singletons
+            out(monoidBuilderValue.longPlusMonoid)
+
+          case _: SigmaDslBuilder =>
+            // always return the same value since SigmaDslBuilder is singleton
+            out(sigmaDslBuilderValue)
+
+          case _: CollBuilder | _: CostedBuilder | _: WSpecialPredefCompanion =>
+            out(dataEnv.getOrElse(sym, {
+               !!!(s"Cannot resolve companion instance for $sym -> ${sym.node}")
+            }))
 
           case SigmaM.isValid(In(prop: AnyRef)) =>
             out(prop)
@@ -852,6 +780,91 @@ trait Evaluation extends RuntimeCosting { IR: IRContext =>
 object Evaluation {
   import special.sigma._
   import special.collection._
+  import OpCodes._
+
+  val AllowedOpCodesInCosting: HashSet[OpCodeExtra] = HashSet[OpCode](
+    AppendCode,
+    ByIndexCode,
+    ConstantCode,
+    DivisionCode,
+    DowncastCode,
+    ExtractBytesWithNoRefCode,
+    ExtractRegisterAs,
+    ExtractScriptBytesCode,
+    FoldCode,
+    FuncApplyCode,
+    FuncValueCode,
+    GetVarCode,
+    InputsCode,
+    LastBlockUtxoRootHashCode,
+    MapCollectionCode,
+    FlatMapCollectionCode,
+    MaxCode,
+    MethodCallCode,
+    MinCode,
+    MinusCode,
+    ModuloCode,
+    MultiplyCode,
+    OptionGetCode,
+    OptionGetOrElseCode,
+    OptionIsDefinedCode,
+    OutputsCode,
+    PlusCode,
+    SelectFieldCode,
+    SelfCode,
+    SigmaPropBytesCode,
+    SizeOfCode,
+    SliceCode,
+    TupleCode,
+    UpcastCode
+  ).map(toExtra) ++ HashSet[OpCodeExtra](
+    OpCostCode,
+    PerKbCostOfCode,
+    CastCode,
+    IntPlusMonoidCode,
+    ThunkDefCode,
+    ThunkForceCode,
+    SCMInputsCode,
+    SCMOutputsCode,
+    SCMDataInputsCode,
+    SCMSelfBoxCode,
+    SCMLastBlockUtxoRootHashCode,
+    SCMHeadersCode,
+    SCMPreHeaderCode,
+    SCMGetVarCode,
+    SBMPropositionBytesCode,
+    SBMBytesCode,
+    SBMBytesWithoutRefCode,
+    SBMRegistersCode,
+    SBMGetRegCode,
+    SBMTokensCode,
+    SSPMPropBytesCode,
+    SAVMTValCode,
+    SAVMValueSizeCode,
+    SizeMDataSizeCode,
+    SPairLCode,
+    SPairRCode,
+    SCollMSizesCode,
+    SOptMSizeOptCode,
+    SFuncMSizeEnvCode,
+    CSizePairCtorCode,
+    CSizeFuncCtorCode,
+    CSizeOptionCtorCode,
+    CSizeCollCtorCode,
+    CSizeBoxCtorCode,
+    CSizeContextCtorCode,
+    CSizeAnyValueCtorCode,
+    CReplCollCtorCode,
+    PairOfColsCtorCode,
+    CollMSumCode,
+    CBMReplicateCode,
+    CBMFromItemsCode,
+    CostOfCode,
+    UOSizeOfCode,
+    SPCMSomeCode
+  )
+
+  def msgCostLimitError(cost: Long, limit: Long) = s"Estimated execution cost $cost exceeds the limit $limit"
 
   /** Transforms a serializable ErgoTree type descriptor to the corresponding RType descriptor of SigmaDsl,
     * which is used during evaluation.
@@ -874,15 +887,25 @@ object Evaluation {
     case SGroupElement => GroupElementRType
     case SAvlTree => AvlTreeRType
     case SSigmaProp => SigmaPropRType
-    case STuple(Seq(tpeA, tpeB)) =>
+    case tup: STuple if tup.items.length == 2 =>
+      val tpeA = tup.items(0)
+      val tpeB = tup.items(1)
       pairRType(stypeToRType(tpeA), stypeToRType(tpeB))
     case STuple(items) =>
       val types = items.toArray
-      tupleRType(types.map(t => stypeToRType(t).asInstanceOf[SomeType]))
+      val len = types.length
+      val rtypes = new Array[SomeType](len)
+      cfor(0)(_ < len, _ + 1) { i =>
+        rtypes(i) = stypeToRType(types(i)).asInstanceOf[SomeType]
+      }
+      tupleRType(rtypes)
     case c: SCollectionType[a] => collRType(stypeToRType(c.elemType))
     case o: SOption[a] => optionRType(stypeToRType(o.elemType))
-    case SFunc(Seq(tpeArg), tpeRange, Nil) => funcRType(stypeToRType(tpeArg), stypeToRType(tpeRange))
-    case _ => sys.error(s"Don't know how to convert SType $t to RType")
+    case SFunc(args, tpeRange, Nil) if args.length == 1 =>
+      val tpeArg = args(0)
+      funcRType(stypeToRType(tpeArg), stypeToRType(tpeRange))
+    case _ =>
+      sys.error(s"Don't know how to convert SType $t to RType")
   }).asInstanceOf[RType[T#WrappedType]]
 
   /** Transforms RType descriptor of SigmaDsl, which is used during evaluation,
diff --git a/sigmastate/src/main/scala/sigmastate/eval/IRContext.scala b/sigmastate/src/main/scala/sigmastate/eval/IRContext.scala
index 3f5b27b762..9d24faec88 100644
--- a/sigmastate/src/main/scala/sigmastate/eval/IRContext.scala
+++ b/sigmastate/src/main/scala/sigmastate/eval/IRContext.scala
@@ -131,7 +131,7 @@ trait IRContext extends Evaluation with TreeBuilding {
     val totalCost = JMath.addExact(initCost, scaledCost)
     if (totalCost > maxCost) {
       // TODO cover with tests
-      throw new CostLimitException(totalCost, msgCostLimitError(totalCost, maxCost), None)
+      throw new CostLimitException(totalCost, Evaluation.msgCostLimitError(totalCost, maxCost), None)
     }
     totalCost.toInt
   }
diff --git a/sigmastate/src/main/scala/sigmastate/eval/RuntimeCosting.scala b/sigmastate/src/main/scala/sigmastate/eval/RuntimeCosting.scala
index 9cf0178843..02124bac5d 100644
--- a/sigmastate/src/main/scala/sigmastate/eval/RuntimeCosting.scala
+++ b/sigmastate/src/main/scala/sigmastate/eval/RuntimeCosting.scala
@@ -903,8 +903,7 @@ trait RuntimeCosting extends CostingRules { IR: IRContext =>
     (ByteElement,   ByteIsExactIntegral),
     (ShortElement,  ShortIsExactIntegral),
     (IntElement,    IntIsExactIntegral),
-    (LongElement,   LongIsExactIntegral),
-    (bigIntElement, BigIntIsExactIntegral)
+    (LongElement,   LongIsExactIntegral)
   )
   private lazy val elemToExactOrderingMap = Map[Elem[_], ExactOrdering[_]](
     (ByteElement,   ByteIsExactOrdering),
@@ -1232,7 +1231,11 @@ trait RuntimeCosting extends CostingRules { IR: IRContext =>
 
       case BlockValue(binds, res) =>
         var curEnv = env
-        for (vd @ ValDef(n, _, b) <- binds) {
+        val len = binds.length
+        cfor(0)(_ < len, _ + 1) { i =>
+          val vd = binds(i).asInstanceOf[ValDef]
+          val n = vd.id
+          val b = vd.rhs
           if (curEnv.contains(n)) error(s"Variable $n already defined ($n = ${curEnv(n)}", vd.sourceContext.toOption)
           val bC = evalNode(ctx, curEnv, b)
           curEnv = curEnv + (n -> bC)
@@ -1601,10 +1604,17 @@ trait RuntimeCosting extends CostingRules { IR: IRContext =>
         RCCostedPrim(v, opCost(v, Array(lC.cost, rC.cost), costOf(node)), SizeBigInt)
 
       case OR(input) => input match {
-        case ConcreteCollection(items, tpe) =>
-          val itemsC = items.map(item => eval(adaptSigmaBoolean(item)))
-          val res = sigmaDslBuilder.anyOf(colBuilder.fromItems(itemsC.map(_.value): _*))
-          val costs = itemsC.map(_.cost)
+        case ConcreteCollection(items, _) =>
+          val len = items.length
+          val values = new Array[Ref[Boolean]](len)
+          val costs = new Array[Ref[Int]](len)
+          cfor(0)(_ < len, _ + 1) { i =>
+            val item = items(i)
+            val itemC = eval(adaptSigmaBoolean(item))
+            values(i) = itemC.value
+            costs(i) = itemC.cost
+          }
+          val res = sigmaDslBuilder.anyOf(colBuilder.fromItems(values: _*))
           val nOps = costs.length - 1
           val cost = opCost(res, costs, perItemCostOf(node, nOps))
           withConstantSize(res, cost)
@@ -1617,10 +1627,17 @@ trait RuntimeCosting extends CostingRules { IR: IRContext =>
       }
 
       case AND(input) => input match {
-        case ConcreteCollection(items, tpe) =>
-          val itemsC = items.map(item => eval(adaptSigmaBoolean(item)))
-          val res = sigmaDslBuilder.allOf(colBuilder.fromItems(itemsC.map(_.value): _*))
-          val costs = itemsC.map(_.cost)
+        case ConcreteCollection(items, _) =>
+          val len = items.length
+          val values = new Array[Ref[Boolean]](len)
+          val costs = new Array[Ref[Int]](len)
+          cfor(0)(_ < len, _ + 1) { i =>
+            val item = items(i)
+            val itemC = eval(adaptSigmaBoolean(item))
+            values(i) = itemC.value
+            costs(i) = itemC.cost
+          }
+          val res = sigmaDslBuilder.allOf(colBuilder.fromItems(values: _*))
           val nOps = costs.length - 1
           val cost = opCost(res, costs, perItemCostOf(node, nOps))
           withConstantSize(res, cost)
@@ -1633,10 +1650,17 @@ trait RuntimeCosting extends CostingRules { IR: IRContext =>
       }
 
       case XorOf(input) => input match {
-        case ConcreteCollection(items, tpe) =>
-          val itemsC = items.map(item => eval(item))
-          val res = sigmaDslBuilder.xorOf(colBuilder.fromItems(itemsC.map(_.value): _*))
-          val costs = itemsC.map(_.cost)
+        case ConcreteCollection(items, _) =>
+          val len = items.length
+          val values = new Array[Ref[Boolean]](len)
+          val costs = new Array[Ref[Int]](len)
+          cfor(0)(_ < len, _ + 1) { i =>
+            val item = items(i)
+            val itemC = eval(adaptSigmaBoolean(item))
+            values(i) = itemC.value
+            costs(i) = itemC.cost
+          }
+          val res = sigmaDslBuilder.xorOf(colBuilder.fromItems(values: _*))
           val nOps = costs.length - 1
           val cost = opCost(res, costs, perItemCostOf(node, nOps))
           withConstantSize(res, cost)
@@ -1680,16 +1704,30 @@ trait RuntimeCosting extends CostingRules { IR: IRContext =>
         }
 
       case SigmaAnd(items) =>
-        val itemsC = items.map(eval)
-        val res = sigmaDslBuilder.allZK(colBuilder.fromItems(itemsC.map(s => asRep[SigmaProp](s.value)): _*))
-        val costs = itemsC.map(_.cost)
+        val len = items.length
+        val values = new Array[Ref[SigmaProp]](len)
+        val costs = new Array[Ref[Int]](len)
+        cfor(0)(_ < len, _ + 1) { i =>
+          val item = items(i)
+          val itemC = eval(item)
+          values(i) = asRep[SigmaProp](itemC.value)
+          costs(i) = itemC.cost
+        }
+        val res = sigmaDslBuilder.allZK(colBuilder.fromItems(values: _*))
         val cost = opCost(res, costs, perItemCostOf(node, costs.length))
         RCCostedPrim(res, cost, SizeSigmaProposition)
 
       case SigmaOr(items) =>
-        val itemsC = items.map(eval)
-        val res = sigmaDslBuilder.anyZK(colBuilder.fromItems(itemsC.map(s => asRep[SigmaProp](s.value)): _*))
-        val costs = itemsC.map(_.cost)
+        val len = items.length
+        val values = new Array[Ref[SigmaProp]](len)
+        val costs = new Array[Ref[Int]](len)
+        cfor(0)(_ < len, _ + 1) { i =>
+          val item = items(i)
+          val itemC = eval(item)
+          values(i) = asRep[SigmaProp](itemC.value)
+          costs(i) = itemC.cost
+        }
+        val res = sigmaDslBuilder.anyZK(colBuilder.fromItems(values: _*))
         val cost = opCost(res, costs, perItemCostOf(node, costs.length))
         RCCostedPrim(res, cost, SizeSigmaProposition)
 
@@ -1802,8 +1840,29 @@ trait RuntimeCosting extends CostingRules { IR: IRContext =>
       // fallback rule for MethodCall, should be the last case in the list
       case Terms.MethodCall(obj, method, args, typeSubst) if method.objType.coster.isDefined =>
         val objC = eval(obj)
-        val argsC = args.map(eval)
-        val elems = typeSubst.values.toSeq.map(tpe => liftElem(stypeToElem(tpe).asInstanceOf[Elem[Any]]))
+        val argsC: Seq[RCosted[SType#WrappedType]] =
+          if (args.isEmpty)
+            EmptySeqOfSym.asInstanceOf[Seq[RCosted[SType#WrappedType]]]
+          else {
+            val len = args.length
+            val res = new Array[RCosted[SType#WrappedType]](len)
+            cfor(0)(_ < len, _ + 1) { i =>
+              res(i) = eval(args(i))
+            }
+            res
+          }
+        val elems: Seq[Sym] =
+          if (typeSubst.isEmpty)
+            EmptySeqOfSym
+          else {
+            val ts = typeSubst.values.toArray
+            val len = ts.length
+            val res = new Array[Sym](len)
+            cfor(0)(_ < len, _ + 1) { i =>
+              res(i) = liftElem(stypeToElem(ts(i)).asInstanceOf[Elem[Any]])
+            }
+            res
+          }
         method.objType.coster.get(IR)(objC, method, argsC, elems)
 
       case _ =>
diff --git a/sigmastate/src/main/scala/sigmastate/eval/TreeBuilding.scala b/sigmastate/src/main/scala/sigmastate/eval/TreeBuilding.scala
index 92e4018a96..0e8253391a 100644
--- a/sigmastate/src/main/scala/sigmastate/eval/TreeBuilding.scala
+++ b/sigmastate/src/main/scala/sigmastate/eval/TreeBuilding.scala
@@ -1,7 +1,7 @@
 package sigmastate.eval
 
 
-import sigmastate.Values.{BlockValue, BoolValue, Constant, ConstantNode, SValue, SigmaPropConstant, ValDef, ValUse, Value}
+import sigmastate.Values.{BlockItem, BlockValue, BoolValue, Constant, ConstantNode, SValue, SigmaPropConstant, ValDef, ValUse, Value}
 import org.ergoplatform._
 
 import org.ergoplatform.{Height, Inputs, Outputs, Self}
@@ -254,7 +254,7 @@ trait TreeBuilding extends RuntimeCosting { IR: IRContext =>
           case (mth @ SCollection.ZipMethod, Seq(coll)) =>
             val typeSubst = Map(SCollection.tOV -> coll.asCollection[SType].tpe.elemType)
             typeSubst
-          case (mth, _) => SigmaTyper.emptySubst
+          case (mth, _) => SigmaTyper.EmptySubst
         }
         val specMethod = method.withConcreteTypes(typeSubst + (SCollection.tIV -> colTpe.elemType))
         builder.mkMethodCall(col, specMethod, args.toIndexedSeq, Map())
@@ -422,7 +422,7 @@ trait TreeBuilding extends RuntimeCosting { IR: IRContext =>
     }
     val Seq(root) = subG.roots
     val rhs = buildValue(ctx, mainG, curEnv, root, curId, constantsProcessing)
-    val res = if (valdefs.nonEmpty) BlockValue(valdefs.toIndexedSeq, rhs) else rhs
+    val res = if (valdefs.nonEmpty) BlockValue(valdefs.toArray[BlockItem], rhs) else rhs
     res
   }
 
diff --git a/sigmastate/src/main/scala/sigmastate/interpreter/Interpreter.scala b/sigmastate/src/main/scala/sigmastate/interpreter/Interpreter.scala
index 1c78a7f82f..619505720a 100644
--- a/sigmastate/src/main/scala/sigmastate/interpreter/Interpreter.scala
+++ b/sigmastate/src/main/scala/sigmastate/interpreter/Interpreter.scala
@@ -10,7 +10,7 @@ import sigmastate.basics.DLogProtocol.{DLogInteractiveProver, FirstDLogProverMes
 import scorex.util.ScorexLogging
 import sigmastate.SCollection.SByteArray
 import sigmastate.Values._
-import sigmastate.eval.{IRContext, Sized}
+import sigmastate.eval.{IRContext, Sized, Evaluation}
 import sigmastate.lang.Terms.ValueOps
 import sigmastate.basics._
 import sigmastate.interpreter.Interpreter.{ScriptEnv, VerificationResult}
@@ -53,7 +53,7 @@ trait Interpreter extends ScorexLogging {
     val currCost = JMath.addExact(context.initCost, scriptComplexity)
     val remainingLimit = context.costLimit - currCost
     if (remainingLimit <= 0)
-      throw new CostLimitException(currCost, msgCostLimitError(currCost, context.costLimit), None) // TODO cover with tests
+      throw new CostLimitException(currCost, Evaluation.msgCostLimitError(currCost, context.costLimit), None) // TODO cover with tests
 
     val ctx1 = context.withInitCost(currCost).asInstanceOf[CTX]
     (ctx1, script)
@@ -115,7 +115,7 @@ trait Interpreter extends ScorexLogging {
     (res, currContext.value)
   }
 
-  def calcResult(context: special.sigma.Context, calcF: Ref[IR.Context => Any]): special.sigma.SigmaProp = {
+  private def calcResult(context: special.sigma.Context, calcF: Ref[IR.Context => Any]): special.sigma.SigmaProp = {
     import IR._
     import Context._
     import SigmaProp._
@@ -156,7 +156,7 @@ trait Interpreter extends ScorexLogging {
 
       CheckCostFunc(IR)(asRep[Any => Int](costF))
 
-      val costingCtx = context.toSigmaContext(IR, isCost = true)
+      val costingCtx = context.toSigmaContext(isCost = true)
       val estimatedCost = IR.checkCostWithContext(costingCtx, costF, maxCost, initCost).getOrThrow
 
       IR.onEstimatedCost(env, exp, costingRes, costingCtx, estimatedCost)
@@ -164,7 +164,7 @@ trait Interpreter extends ScorexLogging {
       // check calc
       val calcF = costingRes.calcF
       CheckCalcFunc(IR)(calcF)
-      val calcCtx = context.toSigmaContext(IR, isCost = false)
+      val calcCtx = context.toSigmaContext(isCost = false)
       val res = calcResult(calcCtx, calcF)
       SigmaDsl.toSigmaBoolean(res) -> estimatedCost
     }
@@ -232,7 +232,7 @@ trait Interpreter extends ScorexLogging {
       val initCost = JMath.addExact(ergoTree.complexity.toLong, context.initCost)
       val remainingLimit = context.costLimit - initCost
       if (remainingLimit <= 0)
-        throw new CostLimitException(initCost, msgCostLimitError(initCost, context.costLimit), None) // TODO cover with tests
+        throw new CostLimitException(initCost, Evaluation.msgCostLimitError(initCost, context.costLimit), None) // TODO cover with tests
 
       val contextWithCost = context.withInitCost(initCost).asInstanceOf[CTX]
 
diff --git a/sigmastate/src/main/scala/sigmastate/interpreter/InterpreterContext.scala b/sigmastate/src/main/scala/sigmastate/interpreter/InterpreterContext.scala
index ea2470c0e7..5965c533e1 100644
--- a/sigmastate/src/main/scala/sigmastate/interpreter/InterpreterContext.scala
+++ b/sigmastate/src/main/scala/sigmastate/interpreter/InterpreterContext.scala
@@ -64,6 +64,12 @@ trait InterpreterContext {
   /** Creates a new instance with given validation settings. */
   def withValidationSettings(newVs: SigmaValidationSettings): InterpreterContext
 
-  /** Creates `special.sigma.Context` instance based on this context. */
-  def toSigmaContext(IR: Evaluation, isCost: Boolean, extensions: Map[Byte, AnyValue] = Map()): sigma.Context
+  /** Creates `special.sigma.Context` instance based on this context. The created instance
+    * contains all data represented using types form [[special.sigma]] package.
+    * These types are used internally by ErgoTree interpreter.
+    * Thus, this method performs transformation from Ergo to internal Sigma representation
+    * of all context data.
+    * @see sigmastate.eval.Evaluation
+    */
+  def toSigmaContext(isCost: Boolean, extensions: Map[Byte, AnyValue] = Map()): sigma.Context
 }
diff --git a/sigmastate/src/main/scala/sigmastate/lang/SigmaTyper.scala b/sigmastate/src/main/scala/sigmastate/lang/SigmaTyper.scala
index e1b6c1df03..79f24ab509 100644
--- a/sigmastate/src/main/scala/sigmastate/lang/SigmaTyper.scala
+++ b/sigmastate/src/main/scala/sigmastate/lang/SigmaTyper.scala
@@ -36,9 +36,9 @@ class SigmaTyper(val builder: SigmaBuilder, predefFuncRegistry: PredefinedFuncRe
     val global = Global.withPropagatedSrcCtx(srcCtx)
     val node = for {
       pf <- method.irInfo.irBuilder
-      res <- pf.lift((builder, global, method, args, emptySubst))
+      res <- pf.lift((builder, global, method, args, EmptySubst))
     } yield res
-    node.getOrElse(mkMethodCall(global, method, args, emptySubst).withPropagatedSrcCtx(srcCtx))
+    node.getOrElse(mkMethodCall(global, method, args, EmptySubst).withPropagatedSrcCtx(srcCtx))
   }
   /**
     * Rewrite tree to typed tree.  Checks constituent names and types.  Uses
@@ -286,7 +286,7 @@ class SigmaTyper(val builder: SigmaBuilder, predefFuncRegistry: PredefinedFuncRe
                   case None =>
                     error(s"Invalid argument type of method call $mc : expected ${sfunc.tDom}; actual: $actualTypes", mc.sourceContext)
                 }
-              case _ => emptySubst
+              case _ => EmptySubst
             }
             method.irInfo.irBuilder.flatMap(_.lift(builder, newObj, method, newArgs, typeSubst))
               .getOrElse(mkMethodCall(newObj, method, newArgs, typeSubst))
@@ -614,7 +614,7 @@ class SigmaTyper(val builder: SigmaBuilder, predefFuncRegistry: PredefinedFuncRe
 object SigmaTyper {
 
   type STypeSubst = Map[STypeVar, SType]
-  val emptySubst = Map.empty[STypeVar, SType]
+  val EmptySubst = Map.empty[STypeVar, SType]
 
   /** Performs pairwise type unification making sure each type variable is equally
     * substituted in all items. */
@@ -623,7 +623,7 @@ object SigmaTyper {
     val itemsUni = (items1, items2).zipped.map((t1, t2) => unifyTypes(t1,t2))
     if (itemsUni.forall(_.isDefined)) {
       // merge substitutions making sure the same id is equally substituted in all items
-      val merged = itemsUni.foldLeft(emptySubst)((acc, subst) => {
+      val merged = itemsUni.foldLeft(EmptySubst)((acc, subst) => {
         var res = acc
         for ((id, t) <- subst.get) {
           if (res.contains(id) && res(id) != t) return None
@@ -636,7 +636,7 @@ object SigmaTyper {
       None
   }
 
-  private val unifiedWithoutSubst = Some(emptySubst)
+  private val unifiedWithoutSubst = Some(EmptySubst)
 
   /** Finds a substitution `subst` of type variables such that unifyTypes(applySubst(t1, subst), t2) shouldBe Some(emptySubst) */
   def unifyTypes(t1: SType, t2: SType): Option[STypeSubst] = (t1, t2) match {
diff --git a/sigmastate/src/main/scala/sigmastate/lang/Terms.scala b/sigmastate/src/main/scala/sigmastate/lang/Terms.scala
index 1e4d86af83..2b4bc61f11 100644
--- a/sigmastate/src/main/scala/sigmastate/lang/Terms.scala
+++ b/sigmastate/src/main/scala/sigmastate/lang/Terms.scala
@@ -11,6 +11,8 @@ import sigmastate.serialization.OpCodes.OpCode
 import sigmastate.lang.TransformingSigmaBuilder._
 
 import scala.language.implicitConversions
+import scala.collection.mutable.WrappedArray
+import spire.syntax.all.cfor
 
 object Terms {
 
@@ -99,7 +101,7 @@ object Terms {
     * compilation environment value. */
   case class Ident(name: String, tpe: SType = NoType) extends Value[SType] {
     override def companion = Ident
-    override def opType: SFunc = SFunc(Vector(), tpe)
+    override def opType: SFunc = SFunc(WrappedArray.empty, tpe)
   }
   object Ident extends ValueCompanion {
     override def opCode: OpCode = OpCodes.Undefined
@@ -107,6 +109,10 @@ object Terms {
   }
 
   // TODO HF: move to sigmastate.Values
+  /** ErgoTree node which represents application of function `func` to the given arguments.
+    * @param func expression which evaluates to a function
+    * @param args arguments of the function application
+    */
   case class Apply(func: Value[SType], args: IndexedSeq[Value[SType]]) extends Value[SType] {
     override def companion = Apply
     override lazy val tpe: SType = func.tpe match {
@@ -114,7 +120,15 @@ object Terms {
       case tColl: SCollectionType[_] => tColl.elemType
       case _ => NoType
     }
-    override def opType: SFunc = SFunc(Vector(func.tpe +: args.map(_.tpe):_*), tpe)
+    override lazy val opType: SFunc = {
+      val nArgs = args.length
+      val argTypes = new Array[SType](nArgs + 1)
+      argTypes(0) = func.tpe
+      cfor(0)(_ < nArgs, _ + 1) { i =>
+        argTypes(i + 1) = args(i).tpe
+      }
+      SFunc(argTypes, tpe)
+    }
   }
   object Apply extends ValueCompanion {
     override def opCode: OpCode = OpCodes.FuncApplyCode
diff --git a/sigmastate/src/main/scala/sigmastate/serialization/BlockValueSerializer.scala b/sigmastate/src/main/scala/sigmastate/serialization/BlockValueSerializer.scala
index b595af5740..04b05ea70d 100644
--- a/sigmastate/src/main/scala/sigmastate/serialization/BlockValueSerializer.scala
+++ b/sigmastate/src/main/scala/sigmastate/serialization/BlockValueSerializer.scala
@@ -6,6 +6,7 @@ import scorex.util.Extensions._
 import sigmastate.utils.{SigmaByteReader, SigmaByteWriter}
 import ValueSerializer._
 import sigmastate.utils.SigmaByteWriter.{Vlq, U, DataInfo}
+import spire.syntax.all.cfor
 
 case class BlockValueSerializer(cons: (IndexedSeq[BlockItem], Value[SType]) => Value[SType])
   extends ValueSerializer[BlockValue] {
@@ -24,7 +25,16 @@ case class BlockValueSerializer(cons: (IndexedSeq[BlockItem], Value[SType]) => V
 
   override def parse(r: SigmaByteReader): Value[SType] = {
     val itemsSize = r.getUInt().toIntExact
-    val values = (1 to itemsSize).map(_ => r.getValue().asInstanceOf[BlockItem])
+    val values: IndexedSeq[BlockItem] = if (itemsSize == 0)
+      BlockItem.EmptySeq
+    else {
+      // @hotspot: allocate new array only if it is not empty
+      val buf = new Array[BlockItem](itemsSize)
+      cfor(0)(_ < itemsSize, _ + 1) { i =>
+        buf(i) = r.getValue().asInstanceOf[BlockItem]
+      }
+      buf
+    }
     val result = r.getValue()
     cons(values, result)
   }
diff --git a/sigmastate/src/main/scala/sigmastate/serialization/ConcreteCollectionBooleanConstantSerializer.scala b/sigmastate/src/main/scala/sigmastate/serialization/ConcreteCollectionBooleanConstantSerializer.scala
index 8dd4b22be3..500056251a 100644
--- a/sigmastate/src/main/scala/sigmastate/serialization/ConcreteCollectionBooleanConstantSerializer.scala
+++ b/sigmastate/src/main/scala/sigmastate/serialization/ConcreteCollectionBooleanConstantSerializer.scala
@@ -30,10 +30,17 @@ case class ConcreteCollectionBooleanConstantSerializer(cons: (IndexedSeq[Value[S
   override def parse(r: SigmaByteReader): Value[SCollection[SBoolean.type]] = {
     val size = r.getUShort()    // READ
     val bits = r.getBits(size)  // READ
-    val items = new Array[BoolValue](size)
-    cfor(0)(_ < size, _ + 1) { i =>
-      items(i) = BooleanConstant.fromBoolean(bits(i))
+    val items: IndexedSeq[Value[SBoolean.type]] = if (size == 0) {
+      // reusing pre-allocated immutable instances
+      Value.EmptySeq.asInstanceOf[IndexedSeq[Value[SBoolean.type]]]
+    } else {
+      val items = new Array[BoolValue](size)
+      cfor(0)(_ < size, _ + 1) { i =>
+        items(i) = BooleanConstant.fromBoolean(bits(i))
+      }
+      items
     }
     cons(items, SBoolean)
   }
+
 }
diff --git a/sigmastate/src/main/scala/sigmastate/serialization/ConcreteCollectionSerializer.scala b/sigmastate/src/main/scala/sigmastate/serialization/ConcreteCollectionSerializer.scala
index d5e41465a1..82c3e24f22 100644
--- a/sigmastate/src/main/scala/sigmastate/serialization/ConcreteCollectionSerializer.scala
+++ b/sigmastate/src/main/scala/sigmastate/serialization/ConcreteCollectionSerializer.scala
@@ -25,11 +25,18 @@ case class ConcreteCollectionSerializer(cons: (IndexedSeq[Value[SType]], SType)
   override def parse(r: SigmaByteReader): Value[SCollection[SType]] = {
     val size = r.getUShort()   // READ
     val tItem = r.getType()    // READ
-    val values = new Array[SValue](size)
-    cfor(0)(_ < size, _ + 1) { i =>
-      values(i) = r.getValue() // READ
+    val values: IndexedSeq[Value[SType]] = if (size == 0) {
+      // reusing pre-allocated immutable instances
+      Value.EmptySeq
+    } else {
+      val values = new Array[SValue](size)
+      cfor(0)(_ < size, _ + 1) { i =>
+        val v = r.getValue() // READ
+        values(i) = v
+        assert(v.tpe == tItem, s"Invalid type of collection value in $values")
+      }
+      values
     }
-    assert(values.forall(_.tpe == tItem), s"Invalid type of collection value in $values")
     cons(values, tItem)
   }
 }
diff --git a/sigmastate/src/main/scala/sigmastate/serialization/ConstantStore.scala b/sigmastate/src/main/scala/sigmastate/serialization/ConstantStore.scala
index 70e9bbf8a6..0bd4588828 100644
--- a/sigmastate/src/main/scala/sigmastate/serialization/ConstantStore.scala
+++ b/sigmastate/src/main/scala/sigmastate/serialization/ConstantStore.scala
@@ -6,7 +6,7 @@ import sigmastate.lang.SigmaBuilder
 import debox.Buffer
 
 /** @hotspot used in deserialization (don't beautify this code) */
-class ConstantStore(private val constants: IndexedSeq[Constant[SType]] = Array[Constant[SType]]()) {
+class ConstantStore(private val constants: IndexedSeq[Constant[SType]] = Constant.EmptySeq) {
 
   private val store: Buffer[Constant[SType]] = Buffer.fromIterable(constants)
 
diff --git a/sigmastate/src/main/scala/sigmastate/serialization/ErgoTreeSerializer.scala b/sigmastate/src/main/scala/sigmastate/serialization/ErgoTreeSerializer.scala
index 719cb576cc..279f0866b0 100644
--- a/sigmastate/src/main/scala/sigmastate/serialization/ErgoTreeSerializer.scala
+++ b/sigmastate/src/main/scala/sigmastate/serialization/ErgoTreeSerializer.scala
@@ -210,22 +210,28 @@ class ErgoTreeSerializer {
   /** Deserialize constants section only.
     * @hotspot don't beautify this code
     */
-  private def deserializeConstants(header: Byte, r: SigmaByteReader): Array[Constant[SType]] = {
-    val constants = if (ErgoTree.isConstantSegregation(header)) {
-      val nConsts = r.getUInt().toInt
-      val res = new Array[Constant[SType]](nConsts)
-      cfor(0)(_ < nConsts, _ + 1) { i =>
-        res(i) = constantSerializer.deserialize(r)
+  private def deserializeConstants(header: Byte, r: SigmaByteReader): IndexedSeq[Constant[SType]] = {
+    val constants: IndexedSeq[Constant[SType]] =
+      if (ErgoTree.isConstantSegregation(header)) {
+        val nConsts = r.getUInt().toInt
+        if (nConsts > 0) {
+          // @hotspot: allocate new array only if it is not empty
+          val res = new Array[Constant[SType]](nConsts)
+          cfor(0)(_ < nConsts, _ + 1) { i =>
+            res(i) = constantSerializer.deserialize(r)
+          }
+          res
+        }
+        else
+          Constant.EmptySeq
       }
-      res
-    }
-    else
-      Array.empty[Constant[SType]]
+      else
+        Constant.EmptySeq
     constants
   }
 
   /** Deserialize header and constant sections, but output the rest of the bytes as separate array. */
-  def deserializeHeaderWithTreeBytes(r: SigmaByteReader): (Byte, Option[Int], Array[Constant[SType]], Array[Byte]) = {
+  def deserializeHeaderWithTreeBytes(r: SigmaByteReader): (Byte, Option[Int], IndexedSeq[Constant[SType]], Array[Byte]) = {
     val (header, sizeOpt) = deserializeHeaderAndSize(r)
     val constants = deserializeConstants(header, r)
     val treeBytes = r.getBytes(r.remaining)
diff --git a/sigmastate/src/main/scala/sigmastate/serialization/FuncValueSerializer.scala b/sigmastate/src/main/scala/sigmastate/serialization/FuncValueSerializer.scala
index a5e41fdbb2..5448963a65 100644
--- a/sigmastate/src/main/scala/sigmastate/serialization/FuncValueSerializer.scala
+++ b/sigmastate/src/main/scala/sigmastate/serialization/FuncValueSerializer.scala
@@ -6,8 +6,7 @@ import scorex.util.Extensions._
 import sigmastate.utils.{SigmaByteReader, SigmaByteWriter}
 import ValueSerializer._
 import sigmastate.utils.SigmaByteWriter.{DataInfo, U, Vlq}
-
-import scala.collection.mutable
+import spire.syntax.all.cfor
 
 case class FuncValueSerializer(cons: (IndexedSeq[(Int, SType)], Value[SType]) => Value[SType])
   extends ValueSerializer[FuncValue] {
@@ -28,14 +27,14 @@ case class FuncValueSerializer(cons: (IndexedSeq[(Int, SType)], Value[SType]) =>
 
   override def parse(r: SigmaByteReader): Value[SType] = {
     val argsSize = r.getUInt().toIntExact
-    val argsBuilder = mutable.ArrayBuilder.make[(Int, SType)]()
-    for (_ <- 0 until argsSize) {
+    val args = new Array[(Int, SType)](argsSize)
+    cfor(0)(_ < argsSize, _ + 1) { i =>
       val id = r.getUInt().toInt
       val tpe = r.getType()
       r.valDefTypeStore(id) = tpe
-      argsBuilder += ((id, tpe))
+      args(i) = (id, tpe)
     }
     val body = r.getValue()
-    cons(argsBuilder.result(), body)
+    cons(args, body)
   }
 }
diff --git a/sigmastate/src/main/scala/sigmastate/serialization/MethodCallSerializer.scala b/sigmastate/src/main/scala/sigmastate/serialization/MethodCallSerializer.scala
index 17dbc964f6..99f4dc29e8 100644
--- a/sigmastate/src/main/scala/sigmastate/serialization/MethodCallSerializer.scala
+++ b/sigmastate/src/main/scala/sigmastate/serialization/MethodCallSerializer.scala
@@ -49,10 +49,17 @@ case class MethodCallSerializer(cons: (Value[SType], SMethod, IndexedSeq[Value[S
     val complexity = ComplexityTable.MethodCallComplexity.getOrElse((typeId, methodId), ComplexityTable.MinimalComplexity)
     r.addComplexity(complexity)
     val nArgs = args.length
-    val types = new Array[SType](nArgs)
-    cfor(0)(_ < nArgs, _ + 1) { i =>
-      types(i) = args(i).tpe
-    }
+
+    val types: Seq[SType] =
+      if (nArgs == 0) SType.EmptySeq
+      else {
+        val types = new Array[SType](nArgs)
+        cfor(0)(_ < nArgs, _ + 1) { i =>
+          types(i) = args(i).tpe
+        }
+        types
+      }
+
     val specMethod = method.specializeFor(obj.tpe, types)
     cons(obj, specMethod, args, Map.empty)
   }
diff --git a/sigmastate/src/main/scala/sigmastate/serialization/PropertyCallSerializer.scala b/sigmastate/src/main/scala/sigmastate/serialization/PropertyCallSerializer.scala
index f382c203e1..3a2ae84002 100644
--- a/sigmastate/src/main/scala/sigmastate/serialization/PropertyCallSerializer.scala
+++ b/sigmastate/src/main/scala/sigmastate/serialization/PropertyCallSerializer.scala
@@ -2,6 +2,7 @@ package sigmastate.serialization
 
 import sigmastate.Values._
 import sigmastate._
+import sigmastate.lang.SigmaTyper
 import sigmastate.lang.SigmaTyper.STypeSubst
 import sigmastate.lang.Terms.{PropertyCall, MethodCall}
 import sigmastate.utils.SigmaByteWriter.DataInfo
@@ -26,11 +27,10 @@ case class PropertyCallSerializer(cons: (Value[SType], SMethod, IndexedSeq[Value
     val typeId = r.getByte()
     val methodId = r.getByte()
     val obj = r.getValue()
-    val args = IndexedSeq()
     val method = SMethod.fromIds(typeId, methodId)
     val complexity = ComplexityTable.MethodCallComplexity.getOrElse((typeId, methodId), ComplexityTable.MinimalComplexity)
     r.addComplexity(complexity)
-    val specMethod = method.specializeFor(obj.tpe, args)
-    cons(obj, specMethod, args, Map())
+    val specMethod = method.specializeFor(obj.tpe, SType.EmptySeq)
+    cons(obj, specMethod, Value.EmptySeq, SigmaTyper.EmptySubst)
   }
 }
diff --git a/sigmastate/src/main/scala/sigmastate/serialization/TupleSerializer.scala b/sigmastate/src/main/scala/sigmastate/serialization/TupleSerializer.scala
index 0578f4dc66..f579803f62 100644
--- a/sigmastate/src/main/scala/sigmastate/serialization/TupleSerializer.scala
+++ b/sigmastate/src/main/scala/sigmastate/serialization/TupleSerializer.scala
@@ -5,6 +5,7 @@ import sigmastate.Values._
 import sigmastate.utils.{SigmaByteReader, SigmaByteWriter}
 import ValueSerializer._
 import sigmastate.utils.SigmaByteWriter.{DataInfo, U}
+import spire.syntax.all.cfor
 
 case class TupleSerializer(cons: Seq[Value[SType]] => Value[SType])
   extends ValueSerializer[Tuple] {
@@ -22,7 +23,10 @@ case class TupleSerializer(cons: Seq[Value[SType]] => Value[SType])
 
   override def parse(r: SigmaByteReader): Value[SType] = {
     val size = r.getByte()
-    val values =  (1 to size).map(_ => r.getValue())
+    val values = new Array[SValue](size) // assume size > 0 so always create a new array
+    cfor(0)(_ < size, _ + 1) { i =>
+      values(i) = r.getValue()
+    }
     cons(values)
   }
 
diff --git a/sigmastate/src/main/scala/sigmastate/serialization/ValDefSerializer.scala b/sigmastate/src/main/scala/sigmastate/serialization/ValDefSerializer.scala
index 8d83ea0b21..e485df7580 100644
--- a/sigmastate/src/main/scala/sigmastate/serialization/ValDefSerializer.scala
+++ b/sigmastate/src/main/scala/sigmastate/serialization/ValDefSerializer.scala
@@ -39,7 +39,7 @@ case class ValDefSerializer(override val opDesc: ValueCompanion) extends ValueSe
         }
         inputs
       case ValDefCode =>
-        Nil
+        STypeVar.EmptySeq
     }
     val rhs = r.getValue()
     r.valDefTypeStore(id) = rhs.tpe
diff --git a/sigmastate/src/main/scala/sigmastate/trees.scala b/sigmastate/src/main/scala/sigmastate/trees.scala
index eb56661cd2..117d0308bd 100644
--- a/sigmastate/src/main/scala/sigmastate/trees.scala
+++ b/sigmastate/src/main/scala/sigmastate/trees.scala
@@ -15,7 +15,7 @@ import sigmastate.utxo.{Transformer, SimpleTransformerCompanion}
 
 import scala.collection.mutable
 import scala.collection.mutable.ArrayBuffer
-
+import spire.syntax.all.cfor
 
 /**
   * Basic trait for inner nodes of crypto-trees, so AND/OR/THRESHOLD sigma-protocol connectives
@@ -41,10 +41,19 @@ case class CAND(override val children: Seq[SigmaBoolean]) extends SigmaConjectur
 
 object CAND {
   import TrivialProp._
+
+  /** Connects the given sigma propositions into CAND proposition performing
+    * partial evaluation when some of them are trivial propositioins.
+    *
+    * @param items propositions to combine into CAND
+    * @return CAND, TrueProp, FalseProp or even one of the items depending on partial evaluation
+    */
   def normalized(items: Seq[SigmaBoolean]): SigmaBoolean = {
     require(items.nonEmpty)
     val res = new ArrayBuffer[SigmaBoolean]()
-    for (x <- items) {
+    val nItems = items.length
+    cfor(0)(_ < nItems, _ + 1) { i =>
+      val x = items(i)
       x match {
         case FalseProp => return FalseProp
         case TrueProp => // skip
@@ -67,10 +76,19 @@ case class COR(children: Seq[SigmaBoolean]) extends SigmaConjecture {
 
 object COR {
   import TrivialProp._
+
+  /** Connects the given sigma propositions into COR proposition performing
+    * partial evaluation when some of them are trivial propositioins.
+    *
+    * @param items propositions to combine into COR
+    * @return COR, TrueProp, FalseProp or even one of the items depending on partial evaluation
+    */
   def normalized(items: Seq[SigmaBoolean]): SigmaBoolean = {
     require(items.nonEmpty)
     val res = new ArrayBuffer[SigmaBoolean]()
-    for (x <- items) {
+    val nItems = items.length
+    cfor(0)(_ < nItems, _ + 1) { i =>
+      val x = items(i)
       x match {
         case FalseProp => // skip
         case TrueProp => return TrueProp
@@ -153,11 +171,11 @@ case class CreateAvlTree(operationFlags: ByteValue,
     valueLengthOpt: Value[SIntOption]) extends AvlTreeValue {
   override def companion = CreateAvlTree
   override def tpe = SAvlTree
-  override def opType = CreateAvlTree.opType
+  override def opType = CreateAvlTree.OpType
 }
 object CreateAvlTree extends ValueCompanion {
   override def opCode: OpCode = OpCodes.AvlTreeCode
-  val opType = SFunc(IndexedSeq(SByte, SByteArray, SInt, SIntOption), SAvlTree)
+  val OpType = SFunc(Array(SByte, SByteArray, SInt, SIntOption), SAvlTree)
 }
 
 /** ErgoTree operation to create a new SigmaProp value representing public key
diff --git a/sigmastate/src/main/scala/sigmastate/types.scala b/sigmastate/src/main/scala/sigmastate/types.scala
index 2cec907904..1bc2017caf 100644
--- a/sigmastate/src/main/scala/sigmastate/types.scala
+++ b/sigmastate/src/main/scala/sigmastate/types.scala
@@ -152,6 +152,12 @@ object SType {
   val IndexedSeqOfT1: IndexedSeq[SType] = Array(SType.tT)
   val IndexedSeqOfT2: IndexedSeq[SType] = Array(SType.tT, SType.tT)
 
+  /** Immutable empty array, can be used to avoid repeated allocations. */
+  val EmptyArray = Array.empty[SType]
+
+  /** Immutable empty IndexedSeq, can be used to avoid repeated allocations. */
+  val EmptySeq: IndexedSeq[SType] = EmptyArray
+
   /** All pre-defined types should be listed here. Note, NoType is not listed.
     * Should be in sync with sigmastate.lang.Types.predefTypes. */
   val allPredefTypes = Seq(SBoolean, SByte, SShort, SInt, SLong, SBigInt, SContext, SGlobal, SHeader, SPreHeader, SAvlTree, SGroupElement, SSigmaProp, SString, SBox, SUnit, SAny)
@@ -1336,6 +1342,12 @@ case class STypeVar(name: String) extends SType {
 object STypeVar {
   val TypeCode: TypeCode = 103: Byte
   implicit def liftString(n: String): STypeVar = STypeVar(n)
+
+  /** Immutable empty array, can be used to avoid repeated allocations. */
+  val EmptyArray = Array.empty[STypeVar]
+
+  /** Immutable empty IndexedSeq, can be used to avoid repeated allocations. */
+  val EmptySeq: IndexedSeq[STypeVar] = EmptyArray
 }
 
 case object SBox extends SProduct with SPredefType with SMonoType {
diff --git a/sigmastate/src/main/scala/sigmastate/utils/SigmaByteReader.scala b/sigmastate/src/main/scala/sigmastate/utils/SigmaByteReader.scala
index 1d679c3b53..cf51dd8b5d 100644
--- a/sigmastate/src/main/scala/sigmastate/utils/SigmaByteReader.scala
+++ b/sigmastate/src/main/scala/sigmastate/utils/SigmaByteReader.scala
@@ -2,10 +2,11 @@ package sigmastate.utils
 
 import scorex.util.serialization.Reader
 import sigmastate.SType
-import sigmastate.Values.SValue
-import sigmastate.lang.exceptions.{DeserializeCallDepthExceeded, InputSizeLimitExceeded}
+import sigmastate.Values.{SValue, Value}
+import sigmastate.lang.exceptions.{InputSizeLimitExceeded, DeserializeCallDepthExceeded}
 import sigmastate.serialization._
 import scorex.util.Extensions._
+import spire.syntax.all.cfor
 
 class SigmaByteReader(val r: Reader,
                       var constantStore: ConstantStore,
@@ -117,13 +118,21 @@ class SigmaByteReader(val r: Reader,
     lvl = v
   }
 
+  /** Read sequence of values from this reader.
+    * It first reads the number of values and then reads each value using `getValue` method.
+    *
+    * @return a sequence of zero of more values read
+    */
   @inline def getValues(): IndexedSeq[SValue] = {
     val size = getUInt().toIntExact
-    val xs = new Array[SValue](size)
-    for (i <- 0 until size) {
-      xs(i) = getValue()
+    if (size == 0) Value.EmptySeq // quick short-cut when there is nothing to read
+    else {
+      val xs = new Array[SValue](size)
+      cfor(0)(_ < size, _ + 1) { i =>
+        xs(i) = getValue()
+      }
+      xs
     }
-    xs
   }
 
   private var positionLmt: Int = r.position + r.remaining
diff --git a/sigmastate/src/main/scala/sigmastate/utxo/transformers.scala b/sigmastate/src/main/scala/sigmastate/utxo/transformers.scala
index bed8d10335..2c79e001e6 100644
--- a/sigmastate/src/main/scala/sigmastate/utxo/transformers.scala
+++ b/sigmastate/src/main/scala/sigmastate/utxo/transformers.scala
@@ -231,10 +231,14 @@ case class ExtractRegisterAs[V <: SType]( input: Value[SBox.type],
                                           override val tpe: SOption[V])
   extends Extract[SOption[V]] with NotReadyValue[SOption[V]] {
   override def companion = ExtractRegisterAs
-  override val opType = SFunc(Array(SBox, SByte), tpe)
+  override val opType = SFunc(ExtractRegisterAs.BoxAndByte, tpe)
 }
 object ExtractRegisterAs extends ValueCompanion {
   override def opCode: OpCode = OpCodes.ExtractRegisterAs
+
+  //@hotspot: avoids thousands of allocations per second
+  private val BoxAndByte: IndexedSeq[SType] = Array(SBox, SByte)
+
   def apply[V <: SType](input: Value[SBox.type],
                         registerId: RegisterId)(implicit tpe: V): ExtractRegisterAs[V] =
     ExtractRegisterAs(input, registerId, SOption(tpe))
diff --git a/sigmastate/src/test/scala/org/ergoplatform/dsl/TestContractSpec.scala b/sigmastate/src/test/scala/org/ergoplatform/dsl/TestContractSpec.scala
index 1467acf92c..b63e9dbf3d 100644
--- a/sigmastate/src/test/scala/org/ergoplatform/dsl/TestContractSpec.scala
+++ b/sigmastate/src/test/scala/org/ergoplatform/dsl/TestContractSpec.scala
@@ -88,7 +88,7 @@ case class TestContractSpec(testSuite: SigmaTestingCommons)(implicit val IR: IRC
       ctx
     }
     def runDsl(extensions: Map[Byte, AnyValue] = Map()): SigmaProp = {
-      val ctx = toErgoContext.toSigmaContext(IR, false, extensions)
+      val ctx = toErgoContext.toSigmaContext(false, extensions)
       val res = utxoBox.propSpec.dslSpec(ctx)
       res
     }
diff --git a/sigmastate/src/test/scala/sigmastate/eval/ErgoScriptTestkit.scala b/sigmastate/src/test/scala/sigmastate/eval/ErgoScriptTestkit.scala
index 2abaf1c128..593806f3f3 100644
--- a/sigmastate/src/test/scala/sigmastate/eval/ErgoScriptTestkit.scala
+++ b/sigmastate/src/test/scala/sigmastate/eval/ErgoScriptTestkit.scala
@@ -173,14 +173,14 @@ trait ErgoScriptTestkit extends ContractsTestkit with LangTests
       }
 
       if (ergoCtx.isDefined) {
-        val calcCtx = ergoCtx.get.toSigmaContext(IR, isCost = false)
+        val calcCtx = ergoCtx.get.toSigmaContext(isCost = false)
         val testContractRes = testContract.map(_(calcCtx))
         testContractRes.foreach { res =>
           checkExpected(res, expectedResult.calc, "Test Contract actual: %s, expected: %s")
         }
 
         // check cost
-        val costCtx = ergoCtx.get.toSigmaContext(IR, isCost = true)
+        val costCtx = ergoCtx.get.toSigmaContext(isCost = true)
         val estimatedCost = IR.checkCost(costCtx, tree, costF, CostTable.ScriptLimit)
 
         // check size
diff --git a/sigmastate/src/test/scala/sigmastate/helpers/SigmaTestingCommons.scala b/sigmastate/src/test/scala/sigmastate/helpers/SigmaTestingCommons.scala
index e41d3cedad..8826339ad4 100644
--- a/sigmastate/src/test/scala/sigmastate/helpers/SigmaTestingCommons.scala
+++ b/sigmastate/src/test/scala/sigmastate/helpers/SigmaTestingCommons.scala
@@ -205,7 +205,7 @@ trait SigmaTestingCommons extends PropSpec
           val ergoCtx = ErgoLikeContextTesting.dummy(createBox(0, TrueProp))
               .withBindings(1.toByte -> Constant[SType](x.asInstanceOf[SType#WrappedType], tpeA))
               .withBindings(bindings: _*)
-          val calcCtx = ergoCtx.toSigmaContext(IR, isCost = false).asInstanceOf[CostingDataContext]
+          val calcCtx = ergoCtx.toSigmaContext(isCost = false).asInstanceOf[CostingDataContext]
           val costCtx = calcCtx.copy(isCost = true)
           (costCtx, calcCtx)
       }
diff --git a/sigmastate/src/test/scala/sigmastate/lang/SigmaCompilerTest.scala b/sigmastate/src/test/scala/sigmastate/lang/SigmaCompilerTest.scala
index a2f005ba0f..786c31eeef 100644
--- a/sigmastate/src/test/scala/sigmastate/lang/SigmaCompilerTest.scala
+++ b/sigmastate/src/test/scala/sigmastate/lang/SigmaCompilerTest.scala
@@ -87,8 +87,8 @@ class SigmaCompilerTest extends SigmaTestingCommons with LangTests with ObjectGe
   }
 
   property("global methods") {
-    comp(env, "{ groupGenerator }") shouldBe MethodCall(Global, SGlobal.groupGeneratorMethod, IndexedSeq(), SigmaTyper.emptySubst)
-    comp(env, "{ Global.groupGenerator }") shouldBe MethodCall(Global, SGlobal.groupGeneratorMethod, IndexedSeq(), SigmaTyper.emptySubst)
+    comp(env, "{ groupGenerator }") shouldBe MethodCall(Global, SGlobal.groupGeneratorMethod, IndexedSeq(), SigmaTyper.EmptySubst)
+    comp(env, "{ Global.groupGenerator }") shouldBe MethodCall(Global, SGlobal.groupGeneratorMethod, IndexedSeq(), SigmaTyper.EmptySubst)
     comp(env, "{ Global.xor(arr1, arr2) }") shouldBe Xor(ByteArrayConstant(arr1), ByteArrayConstant(arr2))
     comp(env, "{ xor(arr1, arr2) }") shouldBe Xor(ByteArrayConstant(arr1), ByteArrayConstant(arr2))
   }
diff --git a/sigmastate/src/test/scala/sigmastate/lang/SigmaTyperTest.scala b/sigmastate/src/test/scala/sigmastate/lang/SigmaTyperTest.scala
index 00286d5f25..4926824bb1 100644
--- a/sigmastate/src/test/scala/sigmastate/lang/SigmaTyperTest.scala
+++ b/sigmastate/src/test/scala/sigmastate/lang/SigmaTyperTest.scala
@@ -312,12 +312,12 @@ class SigmaTyperTest extends PropSpec with PropertyChecks with Matchers with Lan
   property("compute unifying type substitution: prim types") {
     import SigmaTyper._
     forAll { t: SPredefType =>
-      unifyTypes(t, t) shouldBe Some(emptySubst)
-      unifyTypes(SAny, t) shouldBe Some(emptySubst)
-      unifyTypes(SAny, SCollection(t)) shouldBe Some(emptySubst)
-      unifyTypes(SCollection(SAny), SCollection(t)) shouldBe Some(emptySubst)
-      unifyTypes(SCollection(SAny), STuple(t, t, t)) shouldBe Some(emptySubst)
-      unifyTypes(SCollection(SAny), STuple(t, STuple(t, t))) shouldBe Some(emptySubst)
+      unifyTypes(t, t) shouldBe Some(EmptySubst)
+      unifyTypes(SAny, t) shouldBe Some(EmptySubst)
+      unifyTypes(SAny, SCollection(t)) shouldBe Some(EmptySubst)
+      unifyTypes(SCollection(SAny), SCollection(t)) shouldBe Some(EmptySubst)
+      unifyTypes(SCollection(SAny), STuple(t, t, t)) shouldBe Some(EmptySubst)
+      unifyTypes(SCollection(SAny), STuple(t, STuple(t, t))) shouldBe Some(EmptySubst)
     }
   }
 
@@ -327,11 +327,11 @@ class SigmaTyperTest extends PropSpec with PropertyChecks with Matchers with Lan
       unifyTypes(t1, t2) shouldBe exp
       exp match {
         case Some(subst) =>
-          unifyTypes(applySubst(t1, subst), t2) shouldBe Some(emptySubst)
+          unifyTypes(applySubst(t1, subst), t2) shouldBe Some(EmptySubst)
         case None =>
       }
     }
-    def check(s1: String, s2: String, exp: Option[STypeSubst] = Some(emptySubst)): Unit = {
+    def check(s1: String, s2: String, exp: Option[STypeSubst] = Some(EmptySubst)): Unit = {
       val t1 = ty(s1); val t2 = ty(s2)
       checkTypes(t1, t2, exp)
     }
@@ -408,7 +408,7 @@ class SigmaTyperTest extends PropSpec with PropertyChecks with Matchers with Lan
       "((Int,Int), Coll[Boolean] => Coll[(Coll[C], Boolean)]) => Int",
       ("A", SInt), ("B", SBoolean))
 
-    unifyTypes(SBoolean, SSigmaProp) shouldBe Some(emptySubst)
+    unifyTypes(SBoolean, SSigmaProp) shouldBe Some(EmptySubst)
     unifyTypes(SSigmaProp, SBoolean) shouldBe None
     check("(Int, Boolean)", "(Int, SigmaProp)")
     check("(Int, Boolean, Boolean)", "(Int, SigmaProp, SigmaProp)")
diff --git a/sigmastate/src/test/scala/sigmastate/utxo/benchmarks/CrowdFundingContract.scala b/sigmastate/src/test/scala/sigmastate/utxo/benchmarks/CrowdFundingContract.scala
deleted file mode 100644
index 1ef6cc5102..0000000000
--- a/sigmastate/src/test/scala/sigmastate/utxo/benchmarks/CrowdFundingContract.scala
+++ /dev/null
@@ -1,26 +0,0 @@
-package sigmastate.utxo.benchmarks
-
-import org.ergoplatform.ErgoLikeContext
-import sigmastate.helpers.{ContextEnrichingTestProvingInterpreter, ErgoLikeTestInterpreter}
-import sigmastate.interpreter.Interpreter
-import sigmastate.utxo.SigmaContract
-
-import scala.util.Try
-
-abstract class CrowdFundingContract(
-                                     val timeout: Int,
-                                     val minToRaise: Long,
-                                     val backerProver: ContextEnrichingTestProvingInterpreter,
-                                     val projectProver: ContextEnrichingTestProvingInterpreter
-) extends SigmaContract {
-  //a blockchain node verifying a block containing a spending transaction
-  val verifier = new ErgoLikeTestInterpreter()(backerProver.IR)
-  val backerPubKey = backerProver.dlogSecrets.head.publicImage
-  val projectPubKey = projectProver.dlogSecrets.head.publicImage
-
-  def prove(ctx: ErgoLikeContext, fakeMessage: Array[Byte]): Array[Byte]
-
-  def verify(proof: Array[Byte],
-             ctx: ErgoLikeContext,
-             fakeMessage: Array[Byte]): Try[Interpreter.VerificationResult]
-}
diff --git a/sigmastate/src/test/scala/sigmastate/utxo/benchmarks/CrowdFundingKernelContract.scala b/sigmastate/src/test/scala/sigmastate/utxo/benchmarks/CrowdFundingKernelContract.scala
deleted file mode 100644
index 8cd0722134..0000000000
--- a/sigmastate/src/test/scala/sigmastate/utxo/benchmarks/CrowdFundingKernelContract.scala
+++ /dev/null
@@ -1,86 +0,0 @@
-package sigmastate.utxo.benchmarks
-
-import java.math.BigInteger
-import java.util
-
-import org.ergoplatform.ErgoLikeContext
-import sigmastate.basics.DLogProtocol.{DLogInteractiveProver, DLogProverInput, FirstDLogProverMessage, ProveDlog}
-import sigmastate.basics.VerifierMessage.Challenge
-import scorex.crypto.hash.Blake2b256
-import sigmastate._
-import sigmastate.helpers.ContextEnrichingTestProvingInterpreter
-import sigmastate.interpreter.{CryptoConstants, Interpreter}
-import sigmastate.utils.Helpers
-
-import scala.util.Try
-
-class CrowdFundingKernelContract(
-                                  timeout: Int,
-                                  minToRaise: Long,
-                                  override val backerProver: ContextEnrichingTestProvingInterpreter,
-                                  override val projectProver: ContextEnrichingTestProvingInterpreter
-) extends CrowdFundingContract(timeout, minToRaise, backerProver, projectProver) {
-
-  def isProven(pubKey: ProveDlog, message: Array[Byte]): projectProver.ProofT = {
-    import projectProver._
-    var su = UnprovenSchnorr(pubKey, None, None, None, simulated = false)
-    val secret = secrets.find {
-      case in: DLogProverInput => in.publicImage == pubKey
-      case _ => false
-    }
-    val secretKnown = secret.isDefined
-    val simulated = !secretKnown
-    val step4: UnprovenTree = if (simulated) {
-      assert(su.challengeOpt.isDefined)
-      DLogInteractiveProver.simulate(su.proposition,su.challengeOpt.get).asInstanceOf[UnprovenTree]
-    } else {
-      val (r, commitment) = DLogInteractiveProver.firstMessage()
-      UnprovenSchnorr(pubKey, Some(commitment), Some(r), None, simulated = false)
-    }
-
-    val commitments = step4 match {
-      case ul: UnprovenLeaf => ul.commitmentOpt.toSeq
-      case _ => ???
-      /*case uc: UnprovenConjecture => uc.childrenCommitments*/ // can't do this anymore because internal nodes no longer have commitments
-    }
-
-    val rootChallenge = Challenge @@ Blake2b256(Helpers.concatBytes(commitments.map(_.bytes) :+ message))
-
-    su = step4.asInstanceOf[UnprovenSchnorr]
-    val privKey = secret.get.asInstanceOf[DLogProverInput]
-    val z = DLogInteractiveProver.secondMessage(privKey, su.randomnessOpt.get, rootChallenge)
-    UncheckedSchnorr(su.proposition, None, rootChallenge, z)
-  }
-
-  def prove(ctx: ErgoLikeContext, message: Array[Byte]): Array[Byte] = {
-    val c1 = ctx.preHeader.height >= timeout //&& isProven(backerPubKey, fakeMessage)
-    val c2 = Array(
-      ctx.preHeader.height < timeout,
-      ctx.spendingTransaction.outputs.exists(out => {
-        out.value >= minToRaise &&
-          util.Arrays.equals(out.propositionBytes, projectPubKey.toSigmaProp.treeWithSegregation.bytes)
-      })
-    ).forall(identity)
-    var proof: projectProver.ProofT = null
-    c1 || (c2 && { proof = isProven(projectPubKey, message); true})
-    SigSerializer.toBytes(proof)
-  }
-
-  def verify(proof: Array[Byte],
-             ctx: ErgoLikeContext,
-             message: Array[Byte]): Try[Interpreter.VerificationResult] = Try {
-    val sn = proof.asInstanceOf[UncheckedSchnorr]
-    val dlog = CryptoConstants.dlogGroup
-    val g = dlog.generator
-    val h = sn.proposition.h
-
-    val a = dlog.multiplyGroupElements(
-      dlog.exponentiate(g, sn.secondMessage.z.underlying()),
-      dlog.inverseOf(dlog.exponentiate(h, new BigInteger(1, sn.challenge))))
-
-    val rootCommitment = FirstDLogProverMessage(a)
-
-    val expectedChallenge = Blake2b256(Helpers.concatBytes(Seq(rootCommitment.bytes, message)))
-    util.Arrays.equals(sn.challenge, expectedChallenge) -> 0
-  }
-}
diff --git a/sigmastate/src/test/scala/sigmastate/utxo/benchmarks/CrowdFundingScriptContract.scala b/sigmastate/src/test/scala/sigmastate/utxo/benchmarks/CrowdFundingScriptContract.scala
deleted file mode 100644
index 24057cca7f..0000000000
--- a/sigmastate/src/test/scala/sigmastate/utxo/benchmarks/CrowdFundingScriptContract.scala
+++ /dev/null
@@ -1,54 +0,0 @@
-package sigmastate.utxo.benchmarks
-
-import org.ergoplatform.ErgoLikeContext
-import sigmastate.SBoolean
-import sigmastate.Values.{Value, SigmaPropValue}
-import sigmastate.helpers.ContextEnrichingTestProvingInterpreter
-import sigmastate.interpreter.Interpreter
-import sigmastate.interpreter.Interpreter._
-import sigmastate.lang.Terms._
-
-import scala.util.Try
-
-class CrowdFundingScriptContract(
-                                  timeout: Int,
-                                  minToRaise: Long,
-                                  override val backerProver: ContextEnrichingTestProvingInterpreter,
-                                  override val projectProver: ContextEnrichingTestProvingInterpreter
-) extends CrowdFundingContract(timeout, minToRaise, backerProver, projectProver) {
-
-  val compiledProposition: SigmaPropValue = {
-    val env = Map(
-      "timeout" -> timeout,
-      "minToRaise" -> minToRaise,
-      "backerPubKey" -> backerPubKey,
-      "projectPubKey" -> projectPubKey
-    )
-    val compiledScript = compiler.compileWithoutCosting(env,
-      """{
-       | val c1 = HEIGHT >= timeout && backerPubKey
-       | val c2 = allOf(Coll(
-       |   HEIGHT < timeout,
-       |   projectPubKey,
-       |   OUTPUTS.exists({ (out: Box) =>
-       |     out.value >= minToRaise && out.propositionBytes == projectPubKey.propBytes
-       |   })
-       | ))
-       | c1 || c2
-       | }
-      """.stripMargin).asSigmaProp
-    compiledScript
-  }
-
-  def prove(ctx: ErgoLikeContext, fakeMessage: Array[Byte]): Array[Byte] = {
-    val proofP = projectProver.prove(compiledProposition, ctx, fakeMessage).get.proof
-    proofP
-  }
-
-  def verify(proof: Array[Byte],
-             ctx: ErgoLikeContext,
-             fakeMessage: Array[Byte]): Try[Interpreter.VerificationResult] = {
-    val res = verifier.verify(emptyEnv, compiledProposition, ctx, proof, fakeMessage)
-    res
-  }
-}
diff --git a/sigmastate/src/test/scala/sigmastate/utxo/benchmarks/CrowdfundingBenchmark.scala b/sigmastate/src/test/scala/sigmastate/utxo/benchmarks/CrowdfundingBenchmark.scala
deleted file mode 100644
index 26f1948312..0000000000
--- a/sigmastate/src/test/scala/sigmastate/utxo/benchmarks/CrowdfundingBenchmark.scala
+++ /dev/null
@@ -1,82 +0,0 @@
-package sigmastate.utxo.benchmarks
-
-
-import org.ergoplatform.{ErgoLikeContext, ErgoScriptPredef}
-import sigmastate.Values._
-import sigmastate._
-import sigmastate.helpers.{ContextEnrichingTestProvingInterpreter, ErgoLikeContextTesting, SigmaTestingCommons}
-import sigmastate.helpers.TestingHelpers._
-import scalan.util.BenchmarkUtil._
-
-class CrowdfundingBenchmark extends SigmaTestingCommons {
-  implicit lazy val IR = new TestingIRContext
-  def createTestContext(contract: CrowdFundingContract): ErgoLikeContext = {
-    val outputToSpend = testBox(10, ErgoScriptPredef.TrueProp, 0)
-    //First case: height < timeout, project is able to claim amount of tokens not less than required threshold
-    val tx1Output1 = testBox(contract.minToRaise, contract.projectPubKey, 0)
-    val tx1Output2 = testBox(1, contract.projectPubKey, 0)
-    //normally this transaction would invalid, but we're not checking it in this test
-    val tx = createTransaction(IndexedSeq(tx1Output1, tx1Output2))
-    val ctx = ErgoLikeContextTesting(
-      currentHeight = contract.timeout - 1, // HEIGHT < timeout,
-      lastBlockUtxoRoot = AvlTreeData.dummy,
-      minerPubkey = ErgoLikeContextTesting.dummyPubkey,
-      boxesToSpend = IndexedSeq(),
-      spendingTransaction = tx,
-      self = outputToSpend)
-    ctx
-  }
-
-  val timeout = 100
-  val minToRaise = 1000L
-  val nIters = 10000
-  val nTasks = 1
-
-  ignore("Evaluation by Precompiled Kernel(!!! ignore)") {
-    runTasks(nTasks) { iTask =>
-      //backer's prover with his private key
-      val backerProver = new ContextEnrichingTestProvingInterpreter
-      //project's prover with his private key
-      val projectProver = new ContextEnrichingTestProvingInterpreter
-      val contract = new CrowdFundingKernelContract(timeout, minToRaise, backerProver, projectProver)
-      val ctx = createTestContext(contract)
-
-      val (ok, time) = measureTime {
-        var res = true
-        for (_ <- 1 to nIters) {
-          val proof = contract.prove(ctx, fakeMessage)
-          res = contract.verify(proof, ctx, fakeMessage).get._1
-          res shouldBe true
-        }
-        res
-      }
-      ok shouldBe true
-      println(s"Task $iTask: Thread ${Thread.currentThread().getId}: Completed $nIters iterations in $time msec")
-    }
-  }
-
-  ignore("Evaluation by Script Interpretation(!!! ignore)") {
-    runTasks(nTasks) { iTask =>
-      //backer's prover with his private key
-      val backerProver = new ContextEnrichingTestProvingInterpreter
-      //project's prover with his private key
-      val projectProver = new ContextEnrichingTestProvingInterpreter
-      val contract = new CrowdFundingScriptContract(timeout, minToRaise, backerProver, projectProver)
-      val ctx = createTestContext(contract)
-
-      val (ok, time) = measureTime {
-        var res = true
-        for (_ <- 1 to nIters) {
-          val proof = contract.prove(ctx, fakeMessage)
-          res = contract.verify(proof, ctx, fakeMessage).get._1
-          res shouldBe true
-        }
-        res
-      }
-      ok shouldBe true
-      println(s"Task $iTask: Thread ${Thread.currentThread().getId}: Completed $nIters iterations in $time msec")
-    }
-  }
-
-
-}
diff --git a/sigmastate/src/test/scala/sigmastate/utxo/examples/LetsSpecification.scala b/sigmastate/src/test/scala/sigmastate/utxo/examples/LetsSpecification.scala
index c3af822427..97746d4381 100644
--- a/sigmastate/src/test/scala/sigmastate/utxo/examples/LetsSpecification.scala
+++ b/sigmastate/src/test/scala/sigmastate/utxo/examples/LetsSpecification.scala
@@ -166,8 +166,7 @@ import scala.util.Random
  some day this article will be continued!
   */
 
-class LetsSpecification extends SigmaTestingCommons {
-  suite =>
+class LetsSpecification extends SigmaTestingCommons { suite =>
   // Not mixed with TestContext since it is not possible to call compiler.compile outside tests if mixed
   implicit lazy val IR: IRContext = new TestingIRContext
 
diff --git a/sigmastate/src/test/scala/special/sigma/SigmaDslSpecification.scala b/sigmastate/src/test/scala/special/sigma/SigmaDslSpecification.scala
index 86b996700f..71e16fb564 100644
--- a/sigmastate/src/test/scala/special/sigma/SigmaDslSpecification.scala
+++ b/sigmastate/src/test/scala/special/sigma/SigmaDslSpecification.scala
@@ -2341,7 +2341,7 @@ class SigmaDslSpecification extends SigmaDslTesting { suite =>
   //    doApply((CFunc[Int, Int](ctx, code), 10))
   //  }
 
-  lazy val ctx = ergoCtx.toSigmaContext(IR, false)
+  lazy val ctx = ergoCtx.toSigmaContext(false)
 
   property("Box properties equivalence") {
     val b1 = CostingBox(
diff --git a/sigmastate/src/test/scala/special/sigma/SigmaDslTesting.scala b/sigmastate/src/test/scala/special/sigma/SigmaDslTesting.scala
index 2d27ab1523..ce066c9f26 100644
--- a/sigmastate/src/test/scala/special/sigma/SigmaDslTesting.scala
+++ b/sigmastate/src/test/scala/special/sigma/SigmaDslTesting.scala
@@ -305,7 +305,7 @@ class SigmaDslTesting extends PropSpec
         // Add additional oparations which are not yet implemented in ErgoScript compiler
         val multisig = sigmastate.AtLeast(
           IntConstant(2),
-          Seq(
+          Array(
             pkAlice,
             DeserializeRegister(ErgoBox.R5, SSigmaProp),  // deserialize pkBob
             DeserializeContext(2, SSigmaProp)))           // deserialize pkCarol
@@ -430,7 +430,7 @@ class SigmaDslTesting extends PropSpec
     FeatureTest(AddedFeature, script, scalaFunc, Option(expectedExpr), oldImpl, newImpl)
   }
 
-  val contextGen: Gen[Context] = ergoLikeContextGen.map(c => c.toSigmaContext(createIR(), isCost = false))
+  val contextGen: Gen[Context] = ergoLikeContextGen.map(c => c.toSigmaContext(isCost = false))
   implicit val arbContext: Arbitrary[Context] = Arbitrary(contextGen)
 
   /** NOTE, this should be `def` to allow overriding of generatorDrivenConfig in derived Spec classes. */
@@ -467,7 +467,7 @@ class SigmaDslTesting extends PropSpec
        printTestCases: Boolean = PrintTestCasesDefault,
        failOnTestVectors: Boolean = FailOnTestVectorsDefault,
        preGeneratedSamples: Option[Seq[A]] = None): Unit = {
-
+    System.gc() // force GC to avoid occasional OOM exception
     val table = Table(("x", "y"), cases:_*)
     forAll(table) { (x: A, expectedRes: Try[B]) =>
       val res = f.checkEquality(x, printTestCases).map(_._1)