Address review comments.

Author: DarkDimius

src/dotty/tools/dotc/core/Hashable.scala

@@ -88,6 +88,10 @@ trait Hashable {
   protected final def doHash(x1: Any, tp2: Type, tps3: List[Type]): Int =
     finishHash(hashing.mix(hashSeed, x1.hashCode), 1, tp2, tps3)
 
+
+  protected final def doHash(x1: Int, x2: Int): Int =
+    finishHash(hashing.mix(hashing.mix(hashSeed, x1), x2), 1)
+
   protected final def addDelta(hc: Int, delta: Int) = avoidNotCached(hc + delta)
 
   private def avoidNotCached(h: Int) = if (h == NotCached) NotCachedAlt else h

src/dotty/tools/dotc/core/Types.scala

@@ -2374,7 +2374,8 @@ object Types {
     // no customized hashCode/equals needed because cycle is broken in PolyType
     override def toString = s"PolyParam(${binder.paramNames(paramNum)})"
 
-    override def computeHash = finishHash(hashing.mix(hashing.mix(hashSeed, paramNum), binder.identityHash), 1)
+    override def computeHash = doHash(paramNum, binder.identityHash)
+
     override def equals(that: Any) = that match {
       case that: PolyParam =>
         (this.binder eq that.binder) && this.paramNum == that.paramNum