Drop more ctx bindings

Author: odersky

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

@@ -85,8 +85,7 @@ trait SymDenotations { thisCtx: Context =>
       case denot: SymDenotation =>
         def explainSym(msg: String) = explain(s"$msg\ndefined = ${denot.definedPeriodsString}")
         if (denot.isOneOf(ValidForeverFlags) || denot.isRefinementClass) true
-        else {
-          implicit val ctx = thisCtx
+        else inContext(thisCtx) {
           val initial = denot.initial
           if ((initial ne denot) || ctx.phaseId != initial.validFor.firstPhaseId)
             ctx.withPhase(initial.validFor.firstPhaseId).traceInvalid(initial)

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

@@ -235,7 +235,8 @@ class TypeComparer(initctx: Context) extends ConstraintHandling[AbsentContext] w
     def firstTry: Boolean = tp2 match {
       case tp2: NamedType =>
         def compareNamed(tp1: Type, tp2: NamedType): Boolean =
-          implicit val ctx: Context = this.ctx
+          val ctx = this.ctx
+          given Context = ctx // optimization for performance
           val info2 = tp2.info
           info2 match
             case info2: TypeAlias =>