Use a fast path when looking up trait setter getters.

Author: sjrd

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

@@ -274,13 +274,9 @@ object NameOps {
     def setterName: TermName = name.exclude(FieldName) ++ str.SETTER_SUFFIX
 
     def getterName: TermName =
-      if name.is(TraitSetterName) then
-        val TraitSetterName(_, original) = name
-        original.getterName
-      else
-        name.exclude(FieldName).mapLast(n =>
-          if (n.endsWith(str.SETTER_SUFFIX)) n.take(n.length - str.SETTER_SUFFIX.length).asSimpleName
-          else n)
+      name.exclude(FieldName).mapLast(n =>
+        if (n.endsWith(str.SETTER_SUFFIX)) n.take(n.length - str.SETTER_SUFFIX.length).asSimpleName
+        else n)
 
     def fieldName: TermName =
       if (name.isSetterName)

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

@@ -120,12 +120,20 @@ class Memoize extends MiniPhase with IdentityDenotTransformer { thisPhase =>
 
     def traitSetterGetter: Symbol =
       /* We have to compare SimpleNames here, because the setter name only
-       * embed the original getter's simple name, not its semantic name.
+       * embeds the original getter's simple name, not its semantic name.
+       * To mitigate the issue, we first try a fast path where we look up the
+       * simple name itself, which works for public fields.
        */
-      val getterSimpleName = sym.asTerm.name.getterName
-      sym.owner.info.decls.find { getter =>
-        getter.is(Accessor) && getter.asTerm.name.toSimpleName == getterSimpleName
-      }
+      val TraitSetterName(_, original) = sym.name
+      val getterSimpleName = original.getterName
+      val ownerInfo = sym.owner.info
+      val fastPath = ownerInfo.decl(getterSimpleName)
+      if fastPath.exists then
+        fastPath.symbol
+      else
+        ownerInfo.decls.find { getter =>
+          getter.is(Accessor) && getter.asTerm.name.toSimpleName == getterSimpleName
+        }
 
     val constantFinalVal = sym.isAllOf(Accessor | Final, butNot = Mutable) && tree.rhs.isInstanceOf[Literal]