Performance improvement: Cache uninstatiated typevars in constraints

Pro: Much faster to iterate through uninstantiated type variables
Con: Constraints can no longer be value classes.

Still this seems to give a net win of ~2%.

1 files changed, 2 insertions, 5 deletions

diff --git a/src/dotty/tools/dotc/typer/Inferencing.scala b/src/dotty/tools/dotc/typer/Inferencing.scala
index cd30f8ff6..a8003f8c2 100644
--- a/src/dotty/tools/dotc/typer/Inferencing.scala
+++ b/src/dotty/tools/dotc/typer/Inferencing.scala
@@ -606,9 +606,7 @@ object Inferencing {
     val constraint = ctx.typerState.constraint
 
     constr.println(s"interpolate undet vars in ${tp.show}, pos = ${tree.pos}, mode = ${ctx.mode}, undets = ${constraint.uninstVars map (tvar => s"${tvar.show}@${tvar.owningTree.pos}")}")
-    constr.println(s"qualifying undet vars: ${constraint.uninstVars filter qualifies map (tvar => s"$tvar / ${tvar.show}")}")
-    constr.println(s"fulltype: $tp") // !!! DEBUG
-    constr.println(s"constraint: ${constraint.show}")
+    constr.println(s"qualifying undet vars: ${constraint.uninstVars filter qualifies map (tvar => s"$tvar / ${tvar.show}")}, constraint: ${constraint.show}")
 
     def qualifies(tvar: TypeVar) = tree contains tvar.owningTree
     val vs = tp.variances(tvar => (constraint contains tvar) && qualifies(tvar))
@@ -623,12 +621,11 @@ object Inferencing {
     if (changed) // instantiations might have uncovered new typevars to interpolate
       interpolateUndetVars(tree)
     else
-      constraint.foreachUninstVar { tvar =>
+      for (tvar <- constraint.uninstVars)
         if (!(vs contains tvar) && qualifies(tvar)) {
           typr.println(s"instantiating non-occurring ${tvar.show} in ${tp.show}")
           tvar.instantiate(fromBelow = true)
         }
-      }
   }
 
   /** Instantiate undetermined type variables to that type `tp` is