Avoid more collection ops in frontend

Author: odersky

compiler/src/dotty/tools/dotc/transform/SymUtils.scala

@@ -22,12 +22,19 @@ object SymUtils {
 
   extension (self: Symbol) {
 
-  /** All traits implemented by a class or trait except for those inherited through the superclass. */
+  /** All traits implemented by a class or trait except for those inherited
+   *  through the superclass. Traits are given in the order they appear in the
+   *  parents clause (which is the reverse of their order in baseClasses)
+   */
   def directlyInheritedTraits(using Context): List[ClassSymbol] = {
     val superCls = self.asClass.superClass
     val baseClasses = self.asClass.baseClasses
     if (baseClasses.isEmpty) Nil
-    else baseClasses.tail.takeWhile(_ ne superCls).reverse
+    else
+      def recur(bcs: List[ClassSymbol], acc: List[ClassSymbol]): List[ClassSymbol] = bcs match
+        case bc :: bcs1 => if bc eq superCls then acc else recur(bcs1, bc :: acc)
+        case nil => acc
+      recur(baseClasses.tail, Nil)
   }
 
   /** All traits implemented by a class, except for those inherited through the superclass.

compiler/src/dotty/tools/dotc/typer/RefChecks.scala

@@ -491,10 +491,9 @@ object RefChecks {
        */
       def missingTermSymbols: List[Symbol] =
         val buf = new mutable.ListBuffer[Symbol]
-        for bc <- clazz.baseClasses
-            sym <- bc.info.decls.toList
-            if sym.is(DeferredTerm) && !isImplemented(sym) && !ignoreDeferred(sym)
-        do buf += sym
+        for bc <- clazz.baseClasses; sym <- bc.info.decls.toList do
+          if sym.is(DeferredTerm) && !isImplemented(sym) && !ignoreDeferred(sym)
+            buf += sym
         buf.toList
 
       // 2. Check that only abstract classes have deferred members