Merge pull request #5082 from lrytz/inlineImplClassCleanup

Cleanups related to the removal of trait impl classes

10 files changed, 70 insertions, 269 deletions

diff --git a/src/compiler/scala/tools/nsc/backend/jvm/BCodeHelpers.scala b/src/compiler/scala/tools/nsc/backend/jvm/BCodeHelpers.scala
index c5fb2d3604..a32c21795d 100644
--- a/src/compiler/scala/tools/nsc/backend/jvm/BCodeHelpers.scala
+++ b/src/compiler/scala/tools/nsc/backend/jvm/BCodeHelpers.scala
@@ -30,8 +30,7 @@ abstract class BCodeHelpers extends BCodeIdiomatic with BytecodeWriters {
    * True for classes generated by the Scala compiler that are considered top-level in terms of
    * the InnerClass / EnclosingMethod classfile attributes. See comment in BTypes.
    */
-  def considerAsTopLevelImplementationArtifact(classSym: Symbol) =
-    classSym.isSpecialized
+  def considerAsTopLevelImplementationArtifact(classSym: Symbol) = classSym.isSpecialized
 
   /**
    * Cache the value of delambdafy == "inline" for each run. We need to query this value many
@@ -146,10 +145,10 @@ abstract class BCodeHelpers extends BCodeIdiomatic with BytecodeWriters {
     assert(classSym.isClass, classSym)
 
     def doesNotExist(method: Symbol) = {
-      //     Value classes. Member methods of value classes exist in the generated box class. However,
-      //     nested methods lifted into a value class are moved to the companion object and don't exist
-      //     in the value class itself. We can identify such nested methods: the initial enclosing class
-      //     is a value class, but the current owner is some other class (the module class).
+      // Value classes. Member methods of value classes exist in the generated box class. However,
+      // nested methods lifted into a value class are moved to the companion object and don't exist
+      // in the value class itself. We can identify such nested methods: the initial enclosing class
+      // is a value class, but the current owner is some other class (the module class).
       val enclCls = nextEnclosingClass(method)
       exitingPickler(enclCls.isDerivedValueClass) && method.owner != enclCls
     }
@@ -171,8 +170,6 @@ abstract class BCodeHelpers extends BCodeIdiomatic with BytecodeWriters {
   private def enclosingClassForEnclosingMethodAttribute(classSym: Symbol): Symbol = {
     assert(classSym.isClass, classSym)
     val r = nextEnclosingClass(nextEnclosing(classSym))
-    // this should be an assertion, but we are more cautious for now as it was introduced before the 2.11.6 minor release
-    if (considerAsTopLevelImplementationArtifact(r)) devWarning(s"enclosing class of $classSym should not be an implementation artifact class: $r")
     r
   }
 
@@ -187,20 +184,11 @@ abstract class BCodeHelpers extends BCodeIdiomatic with BytecodeWriters {
    * on the implementation of GenASM / GenBCode, so they need to be passed in.
    */
   def enclosingMethodAttribute(classSym: Symbol, classDesc: Symbol => String, methodDesc: Symbol => String): Option[EnclosingMethodEntry] = {
-    // trait impl classes are always top-level, see comment in BTypes
+    // specialized classes are always top-level, see comment in BTypes
     if (isAnonymousOrLocalClass(classSym) && !considerAsTopLevelImplementationArtifact(classSym)) {
       val enclosingClass = enclosingClassForEnclosingMethodAttribute(classSym)
-      val methodOpt = enclosingMethodForEnclosingMethodAttribute(classSym) match {
-        case some @ Some(m) =>
-          if (m.owner != enclosingClass) {
-            // This should never happen. In case it does, it prevents emitting an invalid
-            // EnclosingMethod attribute: if the attribute specifies an enclosing method,
-            // it needs to exist in the specified enclosing class.
-            devWarning(s"the owner of the enclosing method ${m.locationString} should be the same as the enclosing class $enclosingClass")
-            None
-          } else some
-        case none => none
-      }
+      val methodOpt = enclosingMethodForEnclosingMethodAttribute(classSym)
+      for (m <- methodOpt) assert(m.owner == enclosingClass, s"the owner of the enclosing method ${m.locationString} should be the same as the enclosing class $enclosingClass")
       Some(EnclosingMethodEntry(
         classDesc(enclosingClass),
         methodOpt.map(_.javaSimpleName.toString).orNull,
@@ -246,14 +234,6 @@ abstract class BCodeHelpers extends BCodeIdiomatic with BytecodeWriters {
    * Build the [[InlineInfo]] for a class symbol.
    */
   def buildInlineInfoFromClassSymbol(classSym: Symbol, classSymToInternalName: Symbol => InternalName, methodSymToDescriptor: Symbol => String): InlineInfo = {
-    val traitSelfType = if (classSym.isTrait) {
-      // The mixin phase uses typeOfThis for the self parameter in implementation class methods.
-      val selfSym = classSym.typeOfThis.typeSymbol
-      if (selfSym != classSym) Some(classSymToInternalName(selfSym)) else None
-    } else {
-      None
-    }
-
     val isEffectivelyFinal = classSym.isEffectivelyFinal
 
     val sam = {
@@ -282,15 +262,16 @@ abstract class BCodeHelpers extends BCodeIdiomatic with BytecodeWriters {
           val name      = methodSym.javaSimpleName.toString // same as in genDefDef
           val signature = name + methodSymToDescriptor(methodSym)
 
-          // Some detours are required here because of changing flags (lateDEFERRED):
-          // 1. Why the phase travel? Concrete trait methods obtain the lateDEFERRED flag in Mixin.
-          //    This makes isEffectivelyFinalOrNotOverridden false, which would prevent non-final
-          //    but non-overridden methods of sealed traits from being inlined.
-          val effectivelyFinal = exitingPickler(methodSym.isEffectivelyFinalOrNotOverridden) && !(methodSym.owner.isTrait && methodSym.isModule)
+          // In `trait T { object O }`, `oSym.isEffectivelyFinalOrNotOverridden` is true, but the
+          // method is abstract in bytecode, `defDef.rhs.isEmpty`. Abstract methods are excluded
+          // so they are not marked final in the InlineInfo attribute.
+          //
+          // However, due to https://github.com/scala/scala-dev/issues/126, this currently does not
+          // work, the abstract accessor for O will be marked effectivelyFinal.
+          val effectivelyFinal = methodSym.isEffectivelyFinalOrNotOverridden && !methodSym.isDeferred
 
           val info = MethodInlineInfo(
             effectivelyFinal                    = effectivelyFinal,
-            traitMethodWithStaticImplementation = false,
             annotatedInline                     = methodSym.hasAnnotation(ScalaInlineClass),
             annotatedNoInline                   = methodSym.hasAnnotation(ScalaNoInlineClass)
           )
@@ -298,7 +279,7 @@ abstract class BCodeHelpers extends BCodeIdiomatic with BytecodeWriters {
         }
     }).toMap
 
-    InlineInfo(traitSelfType, isEffectivelyFinal, sam, methodInlineInfos, warning)
+    InlineInfo(isEffectivelyFinal, sam, methodInlineInfos, warning)
   }
 
   /*
diff --git a/src/compiler/scala/tools/nsc/backend/jvm/BCodeSkelBuilder.scala b/src/compiler/scala/tools/nsc/backend/jvm/BCodeSkelBuilder.scala
index 20b1a52818..4c41cfc380 100644
--- a/src/compiler/scala/tools/nsc/backend/jvm/BCodeSkelBuilder.scala
+++ b/src/compiler/scala/tools/nsc/backend/jvm/BCodeSkelBuilder.scala
@@ -232,13 +232,6 @@ abstract class BCodeSkelBuilder extends BCodeHelpers {
     }
 
     def addClassFields() {
-      /*  Non-method term members are fields, except for module members. Module
-       *  members can only happen on .NET (no flatten) for inner traits. There,
-       *  a module symbol is generated (transformInfo in mixin) which is used
-       *  as owner for the members of the implementation class (so that the
-       *  backend emits them as static).
-       *  No code is needed for this module symbol.
-       */
       for (f <- fieldSymbols(claszSymbol)) {
         val javagensig = getGenericSignature(f, claszSymbol)
         val flags = javaFieldFlags(f)
diff --git a/src/compiler/scala/tools/nsc/backend/jvm/BTypes.scala b/src/compiler/scala/tools/nsc/backend/jvm/BTypes.scala
index c3f6399901..f6bccca050 100644
--- a/src/compiler/scala/tools/nsc/backend/jvm/BTypes.scala
+++ b/src/compiler/scala/tools/nsc/backend/jvm/BTypes.scala
@@ -255,13 +255,11 @@ abstract class BTypes {
       val methodInfos = classNode.methods.asScala.map(methodNode => {
         val info = MethodInlineInfo(
           effectivelyFinal                    = BytecodeUtils.isFinalMethod(methodNode),
-          traitMethodWithStaticImplementation = false,
           annotatedInline                     = false,
           annotatedNoInline                   = false)
         (methodNode.name + methodNode.desc, info)
       }).toMap
       InlineInfo(
-        traitImplClassSelfType = None,
         isEffectivelyFinal = BytecodeUtils.isFinalClass(classNode),
         sam = inlinerHeuristics.javaSam(classNode.name),
         methodInfos = methodInfos,
@@ -792,26 +790,17 @@ abstract class BTypes {
    *   }
    *
    *
-   * Traits Members
-   * --------------
-   *
-   * Some trait methods don't exist in the generated interface, but only in the implementation class
-   * (private methods in traits for example). Since EnclosingMethod expresses a source-level property,
-   * but the source-level enclosing method doesn't exist in the classfile, we the enclosing method
-   * is null (the enclosing class is still emitted).
-   * See BCodeAsmCommon.considerAsTopLevelImplementationArtifact
-   *
-   *
-   * Implementation Classes, Specialized Classes, Delambdafy:method closure classes
-   * ------------------------------------------------------------------------------
+   * Specialized Classes, Delambdafy:method closure classes
+   * ------------------------------------------------------
    *
-   * Trait implementation classes and specialized classes are always considered top-level. Again,
-   * the InnerClass / EnclosingMethod attributes describe a source-level properties. The impl
-   * classes are compilation artifacts.
+   * Specialized classes are always considered top-level, as the InnerClass / EnclosingMethod
+   * attributes describe a source-level properties.
    *
    * The same is true for delambdafy:method closure classes. These classes are generated at
    * top-level in the delambdafy phase, no special support is required in the backend.
    *
+   * See also BCodeHelpers.considerAsTopLevelImplementationArtifact.
+   *
    *
    * Mirror Classes
    * --------------
@@ -1139,22 +1128,8 @@ object BTypes {
    * Note that this class should contain information that can only be obtained from the ClassSymbol.
    * Information that can be computed from the ClassNode should be added to the call graph instead.
    *
-   * @param traitImplClassSelfType `Some(tp)` if this InlineInfo describes a trait, and the `self`
-   *                               parameter type of the methods in the implementation class is not
-   *                               the trait itself. Example:
-   *                                 trait T { self: U => def f = 1 }
-   *                               Generates something like:
-   *                                 class T$class { static def f(self: U) = 1 }
-   *
-   *                               In order to inline a trat method call, the INVOKEINTERFACE is
-   *                               rewritten to an INVOKESTATIC of the impl class, so we need the
-   *                               self type (U) to get the right signature.
-   *
-   *                               `None` if the self type is the interface type, or if this
-   *                               InlineInfo does not describe a trait.
-   *
    * @param isEffectivelyFinal     True if the class cannot have subclasses: final classes, module
-   *                               classes, trait impl classes.
+   *                               classes.
    *
    * @param sam                    If this class is a SAM type, the SAM's "$name$descriptor".
    *
@@ -1166,26 +1141,21 @@ object BTypes {
    *                               InlineInfo, for example if some classfile could not be found on
    *                               the classpath. This warning can be reported later by the inliner.
    */
-  final case class InlineInfo(traitImplClassSelfType: Option[InternalName],
-                              isEffectivelyFinal: Boolean,
+  final case class InlineInfo(isEffectivelyFinal: Boolean,
                               sam: Option[String],
                               methodInfos: Map[String, MethodInlineInfo],
                               warning: Option[ClassInlineInfoWarning])
 
-  val EmptyInlineInfo = InlineInfo(None, false, None, Map.empty, None)
+  val EmptyInlineInfo = InlineInfo(false, None, Map.empty, None)
 
   /**
    * Metadata about a method, used by the inliner.
    *
    * @param effectivelyFinal                    True if the method cannot be overridden (in Scala)
-   * @param traitMethodWithStaticImplementation True if the method is an interface method method of
-   *                                            a trait method and has a static counterpart in the
-   *                                            implementation class.
    * @param annotatedInline                     True if the method is annotated `@inline`
    * @param annotatedNoInline                   True if the method is annotated `@noinline`
    */
   final case class MethodInlineInfo(effectivelyFinal: Boolean,
-                                    traitMethodWithStaticImplementation: Boolean,
                                     annotatedInline: Boolean,
                                     annotatedNoInline: Boolean)
 
diff --git a/src/compiler/scala/tools/nsc/backend/jvm/BTypesFromSymbols.scala b/src/compiler/scala/tools/nsc/backend/jvm/BTypesFromSymbols.scala
index 759b0a615a..d10b6c8dba 100644
--- a/src/compiler/scala/tools/nsc/backend/jvm/BTypesFromSymbols.scala
+++ b/src/compiler/scala/tools/nsc/backend/jvm/BTypesFromSymbols.scala
@@ -96,11 +96,6 @@ class BTypesFromSymbols[G <: Global](val global: G) extends BTypes {
    * scala.Null is mapped to scala.runtime.Null$. This is because there exist no class files
    * for the Nothing / Null. If used for example as a parameter type, we use the runtime classes
    * in the classfile method signature.
-   *
-   * Note that the referenced class symbol may be an implementation class. For example when
-   * compiling a mixed-in method that forwards to the static method in the implementation class,
-   * the class descriptor of the receiver (the implementation class) is obtained by creating the
-   * ClassBType.
    */
   final def classBTypeFromSymbol(classSym: Symbol): ClassBType = {
     assert(classSym != NoSymbol, "Cannot create ClassBType from NoSymbol")
@@ -159,9 +154,6 @@ class BTypesFromSymbols[G <: Global](val global: G) extends BTypes {
 
   /**
    * This method returns the BType for a type reference, for example a parameter type.
-   *
-   * If `t` references a class, typeToBType ensures that the class is not an implementation class.
-   * See also comment on classBTypeFromSymbol, which is invoked for implementation classes.
    */
   final def typeToBType(t: Type): BType = {
     import definitions.ArrayClass
@@ -264,12 +256,12 @@ class BTypesFromSymbols[G <: Global](val global: G) extends BTypes {
    * current phase, for example, after lambdalift, all local classes become member of the enclosing
    * class.
    *
-   * Impl classes are always considered top-level, see comment in BTypes.
+   * Specialized classes are always considered top-level, see comment in BTypes.
    */
   private def memberClassesForInnerClassTable(classSymbol: Symbol): List[Symbol] = classSymbol.info.decls.collect({
     case sym if sym.isClass && !considerAsTopLevelImplementationArtifact(sym) =>
       sym
-    case sym if sym.isModule && !considerAsTopLevelImplementationArtifact(sym) => // impl classes get the lateMODULE flag in mixin
+    case sym if sym.isModule && !considerAsTopLevelImplementationArtifact(sym) =>
       val r = exitingPickler(sym.moduleClass)
       assert(r != NoSymbol, sym.fullLocationString)
       r
@@ -317,7 +309,6 @@ class BTypesFromSymbols[G <: Global](val global: G) extends BTypes {
       )
     }
 
-    // Check for isImplClass: trait implementation classes have NoSymbol as superClass
     // Check for hasAnnotationFlag for SI-9393: the classfile / java source parsers add
     // scala.annotation.Annotation as superclass to java annotations. In reality, java
     // annotation classfiles have superclass Object (like any interface classfile).
@@ -380,8 +371,8 @@ class BTypesFromSymbols[G <: Global](val global: G) extends BTypes {
       }
 
       val companionModuleMembers = if (considerAsTopLevelImplementationArtifact(classSym)) Nil else {
-        // If this is a top-level non-impl (*) class, the member classes of the companion object are
-        // added as members of the class. For example:
+        // If this is a top-level class, the member classes of the companion object are added as
+        // members of the class. For example:
         //   class C { }
         //   object C {
         //     class D
@@ -392,11 +383,6 @@ class BTypesFromSymbols[G <: Global](val global: G) extends BTypes {
         // (done by buildNestedInfo). See comment in BTypes.
         // For consistency, the InnerClass entry for D needs to be present in C - to Java it looks
         // like D is a member of C, not C$.
-        //
-        // (*) We exclude impl classes: if the classfile for the impl class exists on the classpath,
-        // a linkedClass symbol is found for which isTopLevelModule is true, so we end up searching
-        // members of that weird impl-class-module-class-symbol. that search probably cannot return
-        // any classes, but it's better to exclude it.
         val javaCompatMembers = {
           if (linkedClass != NoSymbol && isTopLevelModuleClass(linkedClass))
           // phase travel to exitingPickler: this makes sure that memberClassesForInnerClassTable only sees member
@@ -454,7 +440,7 @@ class BTypesFromSymbols[G <: Global](val global: G) extends BTypes {
     assert(innerClassSym.isClass, s"Cannot build NestedInfo for non-class symbol $innerClassSym")
 
     val isTopLevel = innerClassSym.rawowner.isPackageClass
-    // impl classes are considered top-level, see comment in BTypes
+    // specialized classes are considered top-level, see comment in BTypes
     if (isTopLevel || considerAsTopLevelImplementationArtifact(innerClassSym)) None
     else if (innerClassSym.rawowner.isTerm) {
       // This case should never be reached: the lambdalift phase mutates the rawowner field of all
@@ -592,17 +578,11 @@ class BTypesFromSymbols[G <: Global](val global: G) extends BTypes {
 
   /**
    * True for module classes of modules that are top-level or owned only by objects. Module classes
-   * for such objects will get a MODULE$ flag and a corresponding static initializer.
+   * for such objects will get a MODULE$ field and a corresponding static initializer.
    */
   final def isStaticModuleClass(sym: Symbol): Boolean = {
-    /* (1) Phase travel to to pickler is required to exclude implementation classes; they have the
-     * lateMODULEs after mixin, so isModuleClass would be true.
-     * (2) isStaticModuleClass is a source-level property. See comment on isOriginallyStaticOwner.
-     */
-    exitingPickler { // (1)
-      sym.isModuleClass &&
-      isOriginallyStaticOwner(sym.originalOwner) // (2)
-    }
+    sym.isModuleClass &&
+    isOriginallyStaticOwner(sym.originalOwner) // isStaticModuleClass is a source-level property, see comment on isOriginallyStaticOwner
   }
 
   // legacy, to be removed when the @remote annotation gets removed
diff --git a/src/compiler/scala/tools/nsc/backend/jvm/BackendReporting.scala b/src/compiler/scala/tools/nsc/backend/jvm/BackendReporting.scala
index 13f4738d3d..01206aa6eb 100644
--- a/src/compiler/scala/tools/nsc/backend/jvm/BackendReporting.scala
+++ b/src/compiler/scala/tools/nsc/backend/jvm/BackendReporting.scala
@@ -170,9 +170,6 @@ object BackendReporting {
 
       case MethodInlineInfoError(_, _, _, cause) =>
         s"Error while computing the inline information for method $warningMessageSignature:\n" + cause
-
-      case RewriteTraitCallToStaticImplMethodFailed(_, _, _, cause) =>
-        cause.toString
     }
 
     def emitWarning(settings: ScalaSettings): Boolean = this match {
@@ -182,15 +179,12 @@ object BackendReporting {
       case MethodInlineInfoMissing(_, _, _, None)                   => settings.YoptWarningNoInlineMissingBytecode
 
       case MethodInlineInfoError(_, _, _, cause)                    => cause.emitWarning(settings)
-
-      case RewriteTraitCallToStaticImplMethodFailed(_, _, _, cause) => cause.emitWarning(settings)
     }
   }
 
   case class MethodInlineInfoIncomplete(declarationClass: InternalName, name: String, descriptor: String, cause: ClassInlineInfoWarning) extends CalleeInfoWarning
   case class MethodInlineInfoMissing(declarationClass: InternalName, name: String, descriptor: String, cause: Option[ClassInlineInfoWarning]) extends CalleeInfoWarning
   case class MethodInlineInfoError(declarationClass: InternalName, name: String, descriptor: String, cause: NoClassBTypeInfo) extends CalleeInfoWarning
-  case class RewriteTraitCallToStaticImplMethodFailed(declarationClass: InternalName, name: String, descriptor: String, cause: OptimizerWarning) extends CalleeInfoWarning
 
   sealed trait CannotInlineWarning extends OptimizerWarning {
     def calleeDeclarationClass: InternalName
diff --git a/src/compiler/scala/tools/nsc/backend/jvm/opt/CallGraph.scala b/src/compiler/scala/tools/nsc/backend/jvm/opt/CallGraph.scala
index 3267b9b5df..5f06e13560 100644
--- a/src/compiler/scala/tools/nsc/backend/jvm/opt/CallGraph.scala
+++ b/src/compiler/scala/tools/nsc/backend/jvm/opt/CallGraph.scala
@@ -132,16 +132,16 @@ class CallGraph[BT <: BTypes](val btypes: BT) {
               (declarationClassNode, source) <- byteCodeRepository.classNodeAndSource(declarationClass): Either[OptimizerWarning, (ClassNode, Source)]
             } yield {
                 val declarationClassBType = classBTypeFromClassNode(declarationClassNode)
-                val CallsiteInfo(safeToInline, safeToRewrite, canInlineFromSource, annotatedInline, annotatedNoInline, samParamTypes, warning) = analyzeCallsite(method, declarationClassBType, call, source)
+                val info = analyzeCallsite(method, declarationClassBType, call, source)
+                import info._
                 Callee(
                   callee = method,
                   calleeDeclarationClass = declarationClassBType,
                   safeToInline = safeToInline,
-                  safeToRewrite = false,
                   canInlineFromSource = canInlineFromSource,
                   annotatedInline = annotatedInline,
                   annotatedNoInline = annotatedNoInline,
-                  samParamTypes = samParamTypes,
+                  samParamTypes = info.samParamTypes,
                   calleeInfoWarning = warning)
               }
 
@@ -256,7 +256,7 @@ class CallGraph[BT <: BTypes](val btypes: BT) {
   /**
    * Just a named tuple used as return type of `analyzeCallsite`.
    */
-  private case class CallsiteInfo(safeToInline: Boolean, safeToRewrite: Boolean, canInlineFromSource: Boolean,
+  private case class CallsiteInfo(safeToInline: Boolean, canInlineFromSource: Boolean,
                                   annotatedInline: Boolean, annotatedNoInline: Boolean,
                                   samParamTypes: IntMap[ClassBType],
                                   warning: Option[CalleeInfoWarning])
@@ -300,16 +300,12 @@ class CallGraph[BT <: BTypes](val btypes: BT) {
               receiverType.info.orThrow.inlineInfo.isEffectivelyFinal // (1)
           }
 
-          val isRewritableTraitCall = false
-
           val warning = calleeDeclarationClassBType.info.orThrow.inlineInfo.warning.map(
             MethodInlineInfoIncomplete(calleeDeclarationClassBType.internalName, calleeMethodNode.name, calleeMethodNode.desc, _))
 
           // (1) For invocations of final trait methods, the callee isStaticallyResolved but also
           //     abstract. Such a callee is not safe to inline - it needs to be re-written to the
           //     static impl method first (safeToRewrite).
-          // (2) Final trait methods can be rewritten from the interface to the static implementation
-          //     method to enable inlining.
           CallsiteInfo(
             safeToInline      =
               canInlineFromSource &&
@@ -318,7 +314,6 @@ class CallGraph[BT <: BTypes](val btypes: BT) {
                 !BytecodeUtils.isConstructor(calleeMethodNode) &&
                 !BytecodeUtils.isNativeMethod(calleeMethodNode) &&
                 !BytecodeUtils.hasCallerSensitiveAnnotation(calleeMethodNode),
-            safeToRewrite       = canInlineFromSource && isRewritableTraitCall, // (2)
             canInlineFromSource = canInlineFromSource,
             annotatedInline     = methodInlineInfo.annotatedInline,
             annotatedNoInline   = methodInlineInfo.annotatedNoInline,
@@ -327,12 +322,12 @@ class CallGraph[BT <: BTypes](val btypes: BT) {
 
         case None =>
           val warning = MethodInlineInfoMissing(calleeDeclarationClassBType.internalName, calleeMethodNode.name, calleeMethodNode.desc, calleeDeclarationClassBType.info.orThrow.inlineInfo.warning)
-          CallsiteInfo(false, false, false, false, false, IntMap.empty, Some(warning))
+          CallsiteInfo(false, false, false, false, IntMap.empty, Some(warning))
       }
     } catch {
       case Invalid(noInfo: NoClassBTypeInfo) =>
         val warning = MethodInlineInfoError(calleeDeclarationClassBType.internalName, calleeMethodNode.name, calleeMethodNode.desc, noInfo)
-        CallsiteInfo(false, false, false, false, false, IntMap.empty, Some(warning))
+        CallsiteInfo(false, false, false, false, IntMap.empty, Some(warning))
     }
   }
 
@@ -387,20 +382,18 @@ class CallGraph[BT <: BTypes](val btypes: BT) {
    * @param calleeDeclarationClass The class in which the callee is declared
    * @param safeToInline           True if the callee can be safely inlined: it cannot be overridden,
    *                               and the inliner settings (project / global) allow inlining it.
-   * @param safeToRewrite          True if the callee is the interface method of a concrete trait method
-   *                               that can be safely re-written to the static implementation method.
    * @param annotatedInline        True if the callee is annotated @inline
    * @param annotatedNoInline      True if the callee is annotated @noinline
    * @param samParamTypes          A map from parameter positions to SAM parameter types
    * @param calleeInfoWarning      An inliner warning if some information was not available while
    *                               gathering the information about this callee.
    */
-  final case class Callee(callee: MethodNode, calleeDeclarationClass: ClassBType,
-                          safeToInline: Boolean, safeToRewrite: Boolean, canInlineFromSource: Boolean,
-                          annotatedInline: Boolean, annotatedNoInline: Boolean,
-                          samParamTypes: IntMap[ClassBType],
-                          calleeInfoWarning: Option[CalleeInfoWarning]) {
-    assert(!(safeToInline && safeToRewrite), s"A callee of ${callee.name} can be either safeToInline or safeToRewrite, but not both.")
+  final case class Callee(
+                           callee: MethodNode, calleeDeclarationClass: btypes.ClassBType,
+                           safeToInline: Boolean, canInlineFromSource: Boolean,
+                           annotatedInline: Boolean, annotatedNoInline: Boolean,
+                           samParamTypes: IntMap[btypes.ClassBType],
+                           calleeInfoWarning: Option[CalleeInfoWarning]) {
     override def toString = s"Callee($calleeDeclarationClass.${callee.name})"
   }
 
diff --git a/src/compiler/scala/tools/nsc/backend/jvm/opt/ClosureOptimizer.scala b/src/compiler/scala/tools/nsc/backend/jvm/opt/ClosureOptimizer.scala
index e5d2e030f9..dcfa9ef705 100644
--- a/src/compiler/scala/tools/nsc/backend/jvm/opt/ClosureOptimizer.scala
+++ b/src/compiler/scala/tools/nsc/backend/jvm/opt/ClosureOptimizer.scala
@@ -363,7 +363,6 @@ class ClosureOptimizer[BT <: BTypes](val btypes: BT) {
           callee = bodyMethodNode,
           calleeDeclarationClass = bodyDeclClassType,
           safeToInline = canInlineFromSource,
-          safeToRewrite = false, // the lambda body method is not a trait interface method
           canInlineFromSource = canInlineFromSource,
           annotatedInline = false,
           annotatedNoInline = false,
diff --git a/src/compiler/scala/tools/nsc/backend/jvm/opt/InlineInfoAttribute.scala b/src/compiler/scala/tools/nsc/backend/jvm/opt/InlineInfoAttribute.scala
index c885a29e16..079a9eec9b 100644
--- a/src/compiler/scala/tools/nsc/backend/jvm/opt/InlineInfoAttribute.scala
+++ b/src/compiler/scala/tools/nsc/backend/jvm/opt/InlineInfoAttribute.scala
@@ -27,7 +27,7 @@ import scala.tools.nsc.backend.jvm.BackendReporting.UnknownScalaInlineInfoVersio
  * In principle we could encode the InlineInfo into a Java annotation (instead of a classfile attribute).
  * However, an attribute allows us to save many bits. In particular, note that the strings in an
  * InlineInfo are serialized as references to constants in the constant pool, and those strings
- * (traitImplClassSelfType, method names, method signatures) would exist in there anyway. So the
+ * (method names, method signatures) would exist in there anyway. So the
  * ScalaInlineAttribute remains relatively compact.
  */
 case class InlineInfoAttribute(inlineInfo: InlineInfo) extends Attribute(InlineInfoAttribute.attributeName) {
@@ -48,15 +48,11 @@ case class InlineInfoAttribute(inlineInfo: InlineInfo) extends Attribute(InlineI
     result.putByte(InlineInfoAttribute.VERSION)
 
     var finalSelfSam = 0
-    if (inlineInfo.isEffectivelyFinal)               finalSelfSam |= 1
-    if (inlineInfo.traitImplClassSelfType.isDefined) finalSelfSam |= 2
-    if (inlineInfo.sam.isDefined)                    finalSelfSam |= 4
+    if (inlineInfo.isEffectivelyFinal) finalSelfSam |= 1
+    //                                 finalSelfSam |= 2 // no longer written
+    if (inlineInfo.sam.isDefined)      finalSelfSam |= 4
     result.putByte(finalSelfSam)
 
-    for (selfInternalName <- inlineInfo.traitImplClassSelfType) {
-      result.putShort(cw.newUTF8(selfInternalName))
-    }
-
     for (samNameDesc <- inlineInfo.sam) {
       val (name, desc) = samNameDesc.span(_ != '(')
       result.putShort(cw.newUTF8(name))
@@ -75,10 +71,10 @@ case class InlineInfoAttribute(inlineInfo: InlineInfo) extends Attribute(InlineI
       result.putShort(cw.newUTF8(desc))
 
       var inlineInfo = 0
-      if (info.effectivelyFinal)                    inlineInfo |= 1
-      if (info.traitMethodWithStaticImplementation) inlineInfo |= 2
-      if (info.annotatedInline)                     inlineInfo |= 4
-      if (info.annotatedNoInline)                   inlineInfo |= 8
+      if (info.effectivelyFinal)  inlineInfo |= 1
+      //                          inlineInfo |= 2 // no longer written
+      if (info.annotatedInline)   inlineInfo |= 4
+      if (info.annotatedNoInline) inlineInfo |= 8
       result.putByte(inlineInfo)
     }
 
@@ -106,10 +102,7 @@ case class InlineInfoAttribute(inlineInfo: InlineInfo) extends Attribute(InlineI
       val hasSelf = (finalSelfSam & 2) != 0
       val hasSam  = (finalSelfSam & 4) != 0
 
-      val self = if (!hasSelf) None else {
-        val selfName = nextUTF8()
-        Some(selfName)
-      }
+      if (hasSelf) nextUTF8() // no longer used
 
       val sam = if (!hasSam) None else {
         val name = nextUTF8()
@@ -123,14 +116,14 @@ case class InlineInfoAttribute(inlineInfo: InlineInfo) extends Attribute(InlineI
         val desc = nextUTF8()
 
         val inlineInfo = nextByte()
-        val isFinal                             = (inlineInfo & 1) != 0
-        val traitMethodWithStaticImplementation = (inlineInfo & 2) != 0
-        val isInline                            = (inlineInfo & 4) != 0
-        val isNoInline                          = (inlineInfo & 8) != 0
-        (name + desc, MethodInlineInfo(isFinal, traitMethodWithStaticImplementation, isInline, isNoInline))
+        val isFinal                                = (inlineInfo & 1) != 0
+        // val traitMethodWithStaticImplementation = (inlineInfo & 2) != 0 // no longer used
+        val isInline                               = (inlineInfo & 4) != 0
+        val isNoInline                             = (inlineInfo & 8) != 0
+        (name + desc, MethodInlineInfo(isFinal, isInline, isNoInline))
       }).toMap
 
-      InlineInfoAttribute(InlineInfo(self, isFinal, sam, infos, None))
+      InlineInfoAttribute(InlineInfo(isFinal, sam, infos, None))
     } else {
       val msg = UnknownScalaInlineInfoVersion(cr.getClassName, version)
       InlineInfoAttribute(BTypes.EmptyInlineInfo.copy(warning = Some(msg)))
@@ -140,6 +133,13 @@ case class InlineInfoAttribute(inlineInfo: InlineInfo) extends Attribute(InlineI
 
 object InlineInfoAttribute {
   /**
+   * Notes:
+   *  - `traitImplClassSelfType` is no longer emitted, `hasTraitImplClassSelfType` is always emitted
+   *    as 0. Similarly, `traitMethodWithStaticImplementation` is always emitted 0.
+   *  - When reading an existing attribute where `hasTraitImplClassSelfType` is 1, the
+   *    `traitImplClassSelfType` is ignored. Also the value of `traitMethodWithStaticImplementation`
+   *    is ignored.
+   *
    * [u1]    version
    * [u1]    isEffectivelyFinal (<< 0), hasTraitImplClassSelfType (<< 1), hasSam (<< 2)
    * [u2]?   traitImplClassSelfType (reference)
@@ -159,4 +159,4 @@ object InlineInfoAttribute {
  * In order to instruct the ASM framework to de-serialize the ScalaInlineInfo attribute, we need
  * to pass a prototype instance when running the class reader.
  */
-object InlineInfoAttributePrototype extends InlineInfoAttribute(InlineInfo(null, false, null, null, null))
+object InlineInfoAttributePrototype extends InlineInfoAttribute(InlineInfo(false, null, null, null))
diff --git a/src/compiler/scala/tools/nsc/backend/jvm/opt/Inliner.scala b/src/compiler/scala/tools/nsc/backend/jvm/opt/Inliner.scala
index 32106614e3..a0ef74b46a 100644
--- a/src/compiler/scala/tools/nsc/backend/jvm/opt/Inliner.scala
+++ b/src/compiler/scala/tools/nsc/backend/jvm/opt/Inliner.scala
@@ -27,8 +27,6 @@ class Inliner[BT <: BTypes](val btypes: BT) {
   import backendUtils._
 
   def runInliner(): Unit = {
-//    rewriteFinalTraitMethodInvocations()
-
     for (request <- collectAndOrderInlineRequests) {
       val Right(callee) = request.callsite.callee // collectAndOrderInlineRequests returns callsites with a known callee
 
@@ -70,111 +68,6 @@ class Inliner[BT <: BTypes](val btypes: BT) {
     }
   }
 
-  // Rewriting final trait method callsites to the implementation class enables inlining.
-  def rewriteFinalTraitMethodInvocations(): Unit = {
-    // Collect callsites to rewrite before actually rewriting anything. This prevents changing the
-    // `callsties` map while iterating it.
-    val toRewrite = mutable.ArrayBuffer.empty[Callsite]
-    for (css <- callsites.valuesIterator; cs <- css.valuesIterator if doRewriteTraitCallsite(cs)) toRewrite += cs
-    toRewrite foreach rewriteFinalTraitMethodInvocation
-  }
-
-  /**
-   * True for statically resolved trait callsites that should be rewritten to the static implementation method.
-   */
-  def doRewriteTraitCallsite(callsite: Callsite) = callsite.callee match {
-    case Right(callee) => callee.safeToRewrite
-    case _ => false
-  }
-
-  /**
-   * Rewrite the INVOKEINTERFACE callsite of a final trait method invocation to INVOKESTATIC of the
-   * corresponding method in the implementation class. This enables inlining final trait methods.
-   *
-   * In a final trait method callsite, the callee is safeToInline and the callee method is abstract
-   * (the receiver type is the interface, so the method is abstract).
-   */
-  def rewriteFinalTraitMethodInvocation(callsite: Callsite): Unit = {
-    // The analyzer used below needs to have a non-null frame for the callsite instruction
-    localOpt.minimalRemoveUnreachableCode(callsite.callsiteMethod, callsite.callsiteClass.internalName)
-
-    // If the callsite was eliminated by DCE, do nothing.
-    if (!callGraph.containsCallsite(callsite)) return
-
-    val Right(Callee(callee, calleeDeclarationClass, _, _, canInlineFromSource, annotatedInline, annotatedNoInline, samParamTypes, infoWarning)) = callsite.callee
-
-    val traitMethodArgumentTypes = asm.Type.getArgumentTypes(callee.desc)
-
-    val implClassInternalName = calleeDeclarationClass.internalName + "$class"
-
-    val selfParamTypeV: Either[OptimizerWarning, ClassBType] = calleeDeclarationClass.info.map(_.inlineInfo.traitImplClassSelfType match {
-      case Some(internalName) => classBTypeFromParsedClassfile(internalName)
-      case None               => calleeDeclarationClass
-    })
-
-    def implClassMethodV(implMethodDescriptor: String): Either[OptimizerWarning, MethodNode] = {
-      byteCodeRepository.methodNode(implClassInternalName, callee.name, implMethodDescriptor).map(_._1)
-    }
-
-    // The rewrite reading the implementation class and the implementation method from the bytecode
-    // repository. If either of the two fails, the rewrite is not performed.
-    val res = for {
-      selfParamType        <- selfParamTypeV
-      implMethodDescriptor =  asm.Type.getMethodDescriptor(asm.Type.getReturnType(callee.desc), selfParamType.toASMType +: traitMethodArgumentTypes: _*)
-      implClassMethod      <- implClassMethodV(implMethodDescriptor)
-      implClassBType       =  classBTypeFromParsedClassfile(implClassInternalName)
-      selfTypeOk           <- calleeDeclarationClass.isSubtypeOf(selfParamType)
-    } yield {
-
-      // The self parameter type may be incompatible with the trait type.
-      //   trait T { self: S => def foo = 1 }
-      // The $self parameter type of T$class.foo is S, which may be unrelated to T. If we re-write
-      // a call to T.foo to T$class.foo, we need to cast the receiver to S, otherwise we get a
-      // VerifyError. We run a `SourceInterpreter` to find all producer instructions of the
-      // receiver value and add a cast to the self type after each.
-      if (!selfTypeOk) {
-        // We don't need to worry about the method being too large for running an analysis.
-        // Callsites of large methods are not added to the call graph.
-        val analyzer = new AsmAnalyzer(callsite.callsiteMethod, callsite.callsiteClass.internalName, new Analyzer(new SourceInterpreter))
-        val receiverValue = analyzer.frameAt(callsite.callsiteInstruction).peekStack(traitMethodArgumentTypes.length)
-        for (i <- receiverValue.insns.asScala) {
-          val cast = new TypeInsnNode(CHECKCAST, selfParamType.internalName)
-          callsite.callsiteMethod.instructions.insert(i, cast)
-        }
-      }
-
-      val newCallsiteInstruction = new MethodInsnNode(INVOKESTATIC, implClassInternalName, callee.name, implMethodDescriptor, false)
-      callsite.callsiteMethod.instructions.insert(callsite.callsiteInstruction, newCallsiteInstruction)
-      callsite.callsiteMethod.instructions.remove(callsite.callsiteInstruction)
-
-      callGraph.removeCallsite(callsite.callsiteInstruction, callsite.callsiteMethod)
-      val staticCallSamParamTypes = {
-        if (selfParamType.info.get.inlineInfo.sam.isEmpty) samParamTypes - 0
-        else samParamTypes.updated(0, selfParamType)
-      }
-      val staticCallsite = callsite.copy(
-        callsiteInstruction = newCallsiteInstruction,
-        callee              = Right(Callee(
-          callee                 = implClassMethod,
-          calleeDeclarationClass = implClassBType,
-          safeToInline           = true,
-          safeToRewrite          = false,
-          canInlineFromSource    = canInlineFromSource,
-          annotatedInline        = annotatedInline,
-          annotatedNoInline      = annotatedNoInline,
-          samParamTypes          = staticCallSamParamTypes,
-          calleeInfoWarning      = infoWarning))
-      )
-      callGraph.addCallsite(staticCallsite)
-    }
-
-    for (warning <- res.left) {
-      val Right(callee) = callsite.callee
-      val newCallee = callee.copy(calleeInfoWarning = Some(RewriteTraitCallToStaticImplMethodFailed(calleeDeclarationClass.internalName, callee.callee.name, callee.callee.desc, warning)))
-      callGraph.addCallsite(callsite.copy(callee = Right(newCallee)))
-    }
-  }
-
   /**
    * Returns the callsites that can be inlined. Ensures that the returned inline request graph does
    * not contain cycles.
diff --git a/src/compiler/scala/tools/nsc/backend/jvm/opt/InlinerHeuristics.scala b/src/compiler/scala/tools/nsc/backend/jvm/opt/InlinerHeuristics.scala
index 388c35274b..e132ae1792 100644
--- a/src/compiler/scala/tools/nsc/backend/jvm/opt/InlinerHeuristics.scala
+++ b/src/compiler/scala/tools/nsc/backend/jvm/opt/InlinerHeuristics.scala
@@ -39,7 +39,7 @@ class InlinerHeuristics[BT <: BTypes](val bTypes: BT) {
     compilingMethods.map(methodNode => {
       var requests = Set.empty[InlineRequest]
       callGraph.callsites(methodNode).valuesIterator foreach {
-        case callsite @ Callsite(_, _, _, Right(Callee(callee, calleeDeclClass, safeToInline, _, canInlineFromSource, calleeAnnotatedInline, _, _, callsiteWarning)), _, _, _, pos, _, _) =>
+        case callsite @ Callsite(_, _, _, Right(Callee(callee, calleeDeclClass, safeToInline, canInlineFromSource, calleeAnnotatedInline, _, _, callsiteWarning)), _, _, _, pos, _, _) =>
           inlineRequest(callsite) match {
             case Some(Right(req)) => requests += req
             case Some(Left(w))    =>
@@ -55,9 +55,7 @@ class InlinerHeuristics[BT <: BTypes](val bTypes: BT) {
                 // reason is, for example, mixed compilation (which has a separate -Yopt-warning flag).
                 def initMsg = s"${BackendReporting.methodSignature(calleeDeclClass.internalName, callee)} is annotated @inline but cannot be inlined"
                 def warnMsg = callsiteWarning.map(" Possible reason:\n" + _).getOrElse("")
-                if (doRewriteTraitCallsite(callsite))
-                  backendReporting.inlinerWarning(pos, s"$initMsg: the trait method call could not be rewritten to the static implementation method." + warnMsg)
-                else if (!safeToInline)
+                if (!safeToInline)
                   backendReporting.inlinerWarning(pos, s"$initMsg: the method is not final and may be overridden." + warnMsg)
                 else
                   backendReporting.inlinerWarning(pos, s"$initMsg." + warnMsg)