Some smaller optimizations and refactorings

compiler/src/dotty/tools/dotc/core/Constraint.scala

@@ -121,6 +121,13 @@ abstract class Constraint extends Showable {
   /** A new constraint with entry `tl` renamed to a fresh type lambda */
   def rename(tl: TypeLambda)(using Context): This
 
+  /** Gives for each instantiated type var that does not yet have its `inst` field
+   *  set, the instance value stored in the constraint. Storing instances in constraints
+   *  is done only in a temporary way for contexts that may be retracted
+   *  without also retracting the type var as a whole.
+   */
+  def instType(tvar: TypeVar): Type
+
   /** The given `tl` in case it is not contained in this constraint,
    *  a fresh copy of `tl` otherwise.
    */

compiler/src/dotty/tools/dotc/core/ConstraintHandling.scala

@@ -61,19 +61,6 @@ trait ConstraintHandling {
     assert(homogenizeArgs == false)
     assert(comparedTypeLambdas == Set.empty)
 
-  /** Gives for each instantiated type var that does not yet have its `inst` field
-   *  set, the instance value stored in the constraint. Storing instances in constraints
-   *  is done only in a temporary way for contexts that may be retracted
-   *  without also retracting the type var as a whole.
-   */
-  def instType(tvar: TypeVar): Type = constraint.entry(tvar.origin) match {
-    case _: TypeBounds => NoType
-    case tp: TypeParamRef =>
-      var tvar1 = constraint.typeVarOfParam(tp)
-      if (tvar1.exists) tvar1 else tp
-    case tp => tp
-  }
-
   def nonParamBounds(param: TypeParamRef)(using Context): TypeBounds = constraint.nonParamBounds(param)
 
   def fullLowerBound(param: TypeParamRef)(using Context): Type =

compiler/src/dotty/tools/dotc/core/GadtConstraint.scala

@@ -131,7 +131,7 @@ final class ProperGadtConstraint private(
   override def addBound(sym: Symbol, bound: Type, isUpper: Boolean)(using Context): Boolean = {
     @annotation.tailrec def stripInternalTypeVar(tp: Type): Type = tp match {
       case tv: TypeVar =>
-        val inst = instType(tv)
+        val inst = constraint.instType(tv)
         if (inst.exists) stripInternalTypeVar(inst) else tv
       case _ => tp
     }

compiler/src/dotty/tools/dotc/core/OrderingConstraint.scala

@@ -530,6 +530,11 @@ class OrderingConstraint(private val boundsMap: ParamBounds,
     current.checkNonCyclic()
   }
 
+  def instType(tvar: TypeVar): Type = entry(tvar.origin) match
+    case _: TypeBounds => NoType
+    case tp: TypeParamRef => typeVarOfParam(tp).orElse(tp)
+    case tp => tp
+
   def ensureFresh(tl: TypeLambda)(using Context): TypeLambda =
     if (contains(tl)) {
       var paramInfos = tl.paramInfos

compiler/src/dotty/tools/dotc/core/TypeComparer.scala

@@ -2605,9 +2605,6 @@ object TypeComparer {
   def subtypeCheckInProgress(using Context): Boolean =
     comparing(_.subtypeCheckInProgress)
 
-  def instType(tvar: TypeVar)(using Context): Type =
-    comparing(_.instType(tvar))
-
   def instanceType(param: TypeParamRef, fromBelow: Boolean)(using Context): Type =
     comparing(_.instanceType(param, fromBelow))
 

compiler/src/dotty/tools/dotc/core/TypeOps.scala

@@ -529,74 +529,79 @@ object TypeOps:
     val skolemizedArgTypes = skolemizeWildcardArgs(argTypes, app)
     val violations = new mutable.ListBuffer[BoundsViolation]
 
-    for ((arg, bounds) <- args zip boundss) {
-      def checkOverlapsBounds(lo: Type, hi: Type): Unit = {
-        //println(i" = ${instantiate(bounds.hi, argTypes)}")
-
-        var checkCtx = ctx  // the context to be used for bounds checking
-        if (argTypes ne skolemizedArgTypes) { // some of the arguments are wildcards
-
-          /** Is there a `LazyRef(TypeRef(_, sym))` reference in `tp`? */
-          def isLazyIn(sym: Symbol, tp: Type): Boolean = {
-            def isReference(tp: Type) = tp match {
-              case tp: LazyRef => tp.ref.isInstanceOf[TypeRef] && tp.ref.typeSymbol == sym
-              case _ => false
-            }
-            tp.existsPart(isReference, forceLazy = false)
-          }
+    def checkOverlapsBounds(lo: Type, hi: Type, arg: Tree, bounds: TypeBounds): Unit = {
+      //println(i" = ${instantiate(bounds.hi, argTypes)}")
 
-          /** The argument types of the form `TypeRef(_, sym)` which appear as a LazyRef in `bounds`.
-           *  This indicates that the application is used as an F-bound for the symbol referred to in the LazyRef.
-           */
-          val lazyRefs = skolemizedArgTypes collect {
-            case tp: TypeRef if isLazyIn(tp.symbol, bounds) => tp.symbol
-          }
+      var checkCtx = ctx  // the context to be used for bounds checking
+      if (argTypes ne skolemizedArgTypes) { // some of the arguments are wildcards
 
-          for (sym <- lazyRefs) {
-
-            // If symbol `S` has an F-bound such as `C[?, S]` that contains wildcards,
-            // add a modifieed bound where wildcards are skolemized as a GADT bound for `S`.
-            // E.g. for `C[?, S]` we would add `C[C[?, S]#T0, S]` where `T0` is the first
-            // type parameter of `C`. The new bound is added as a GADT bound for `S` in
-            // `checkCtx`.
-            // This mirrors what we do for the bounds that are checked and allows us thus
-            // to bounds-check F-bounds with wildcards. A test case is pos/i6146.scala.
-
-            def massage(tp: Type): Type = tp match {
-              case tp @ AppliedType(tycon, args) =>
-                tp.derivedAppliedType(tycon, skolemizeWildcardArgs(args, tp))
-              case tp: AndOrType =>
-                tp.derivedAndOrType(massage(tp.tp1), massage(tp.tp2))
-              case _ => tp
-            }
-            def narrowBound(bound: Type, fromBelow: Boolean): Unit = {
-              val bound1 = massage(bound)
-              if (bound1 ne bound) {
-                if (checkCtx eq ctx) checkCtx = ctx.fresh.setFreshGADTBounds
-                if (!checkCtx.gadt.contains(sym)) checkCtx.gadt.addToConstraint(sym)
-                checkCtx.gadt.addBound(sym, bound1, fromBelow)
-                typr.println("install GADT bound $bound1 for when checking F-bounded $sym")
-              }
-            }
-            narrowBound(sym.info.loBound, fromBelow = true)
-            narrowBound(sym.info.hiBound, fromBelow = false)
+        /** Is there a `LazyRef(TypeRef(_, sym))` reference in `tp`? */
+        def isLazyIn(sym: Symbol, tp: Type): Boolean = {
+          def isReference(tp: Type) = tp match {
+            case tp: LazyRef => tp.ref.isInstanceOf[TypeRef] && tp.ref.typeSymbol == sym
+            case _ => false
           }
+          tp.existsPart(isReference, forceLazy = false)
         }
 
-        val hiBound = instantiate(bounds.hi, skolemizedArgTypes)
-        val loBound = instantiate(bounds.lo, skolemizedArgTypes)
+        /** The argument types of the form `TypeRef(_, sym)` which appear as a LazyRef in `bounds`.
+         *  This indicates that the application is used as an F-bound for the symbol referred to in the LazyRef.
+         */
+        val lazyRefs = skolemizedArgTypes collect {
+          case tp: TypeRef if isLazyIn(tp.symbol, bounds) => tp.symbol
+        }
 
-        def check(using Context) = {
-          if (!(lo <:< hiBound)) violations += ((arg, "upper", hiBound))
-          if (!(loBound <:< hi)) violations += ((arg, "lower", loBound))
+        for (sym <- lazyRefs) {
+
+          // If symbol `S` has an F-bound such as `C[?, S]` that contains wildcards,
+          // add a modifieed bound where wildcards are skolemized as a GADT bound for `S`.
+          // E.g. for `C[?, S]` we would add `C[C[?, S]#T0, S]` where `T0` is the first
+          // type parameter of `C`. The new bound is added as a GADT bound for `S` in
+          // `checkCtx`.
+          // This mirrors what we do for the bounds that are checked and allows us thus
+          // to bounds-check F-bounds with wildcards. A test case is pos/i6146.scala.
+
+          def massage(tp: Type): Type = tp match {
+            case tp @ AppliedType(tycon, args) =>
+              tp.derivedAppliedType(tycon, skolemizeWildcardArgs(args, tp))
+            case tp: AndOrType =>
+              tp.derivedAndOrType(massage(tp.tp1), massage(tp.tp2))
+            case _ => tp
+          }
+          def narrowBound(bound: Type, fromBelow: Boolean): Unit = {
+            val bound1 = massage(bound)
+            if (bound1 ne bound) {
+              if (checkCtx eq ctx) checkCtx = ctx.fresh.setFreshGADTBounds
+              if (!checkCtx.gadt.contains(sym)) checkCtx.gadt.addToConstraint(sym)
+              checkCtx.gadt.addBound(sym, bound1, fromBelow)
+              typr.println("install GADT bound $bound1 for when checking F-bounded $sym")
+            }
+          }
+          narrowBound(sym.info.loBound, fromBelow = true)
+          narrowBound(sym.info.hiBound, fromBelow = false)
         }
-        check(using checkCtx)
       }
-      arg.tpe match {
-        case TypeBounds(lo, hi) => checkOverlapsBounds(lo, hi)
-        case tp => checkOverlapsBounds(tp, tp)
+      val hiBound = instantiate(bounds.hi, skolemizedArgTypes)
+      val loBound = instantiate(bounds.lo, skolemizedArgTypes)
+
+      def check(using Context) = {
+        if (!(lo <:< hiBound)) violations += ((arg, "upper", hiBound))
+        if (!(loBound <:< hi)) violations += ((arg, "lower", loBound))
       }
+      check(using checkCtx)
     }
+
+    def loop(args: List[Tree], boundss: List[TypeBounds]): Unit = args match
+      case arg :: args1 => boundss match
+        case bounds :: boundss1 =>
+          arg.tpe match
+            case TypeBounds(lo, hi) => checkOverlapsBounds(lo, hi, arg, bounds)
+            case tp => checkOverlapsBounds(tp, tp, arg, bounds)
+          loop(args1, boundss1)
+        case _ =>
+      case _ =>
+
+    loop(args, boundss)
     violations.toList
   }
 

compiler/src/dotty/tools/dotc/core/TyperState.scala

@@ -138,10 +138,11 @@ class TyperState() {
    *  no-longer needed constraint entries.
    */
   def gc()(using Context): Unit = {
+    Stats.record("typerState.gc")
     val toCollect = new mutable.ListBuffer[TypeLambda]
     constraint foreachTypeVar { tvar =>
       if (!tvar.inst.exists) {
-        val inst = TypeComparer.instType(tvar)
+        val inst = constraint.instType(tvar)
         if (inst.exists && (tvar.owningState.get eq this)) {
           tvar.inst = inst
           val lam = tvar.origin.binder

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

@@ -3211,8 +3211,16 @@ object Types {
       else newLikeThis(paramNames, paramInfos, resType)
 
     def newLikeThis(paramNames: List[ThisName], paramInfos: List[PInfo], resType: Type)(using Context): This =
+      def substParams(pinfos: List[PInfo], to: This): List[PInfo] = pinfos match
+        case pinfo :: rest =>
+          val pinfo1 = pinfo.subst(this, to).asInstanceOf[PInfo]
+          val rest1 = substParams(rest, to)
+          if (pinfo1 eq pinfo) && (rest1 eq rest) then pinfos
+          else pinfo1 :: rest1
+        case nil =>
+          nil
       companion(paramNames)(
-          x => paramInfos.mapConserve(_.subst(this, x).asInstanceOf[PInfo]),
+          x => substParams(paramInfos, x),
           x => resType.subst(this, x))
 
     protected def prefixString: String
@@ -4184,7 +4192,7 @@ object Types {
      *  uninstantiated
      */
     def instanceOpt(using Context): Type =
-      if (inst.exists) inst else TypeComparer.instType(this)
+      if (inst.exists) inst else ctx.typerState.constraint.instType(this)
 
     /** Is the variable already instantiated? */
     def isInstantiated(using Context): Boolean = instanceOpt.exists