Remove dead-code compiler-internal names.

Some were "used" in dead-code methods, which were removed as well.

Some were also "used" in non-dead code that only *detected* the
presence of the name. Those tests would always be false, since no
code would ever create those names in the first place.

Author: sjrd

compiler/src/dotty/tools/backend/jvm/BCodeBodyBuilder.scala

@@ -293,9 +293,6 @@ trait BCodeBodyBuilder extends BCodeSkelBuilder {
       lineNumber(tree)
 
       tree match {
-        case ValDef(nme.THIS, _, _) =>
-          report.debuglog("skipping trivial assign to _$this: " + tree)
-
         case tree@ValDef(_, _, _) =>
           val sym = tree.symbol
           /* most of the time, !locals.contains(sym), unless the current activation of genLoad() is being called

compiler/src/dotty/tools/backend/sjs/JSCodeGen.scala

@@ -1702,11 +1702,6 @@ class JSCodeGen()(using genCtx: Context) {
     tree match {
       /** Local val or var declaration */
       case tree @ ValDef(name, _, _) =>
-        /* Must have been eliminated by the tail call transform performed
-         * by genMethodBody(). */
-        assert(name != nme.THIS,
-            s"ValDef(_, nme.THIS, _, _) found at ${tree.span}")
-
         val sym = tree.symbol
         val rhs = tree.rhs
         val rhsTree = genExpr(rhs)

compiler/src/dotty/tools/dotc/ast/TreeInfo.scala

@@ -215,13 +215,6 @@ trait TreeInfo[T >: Untyped <: Type] { self: Trees.Instance[T] =>
     case _                            => false
   }
 
-  /** Is this pattern node a synthetic catch-all case, added during PartialFuction synthesis before we know
-    * whether the user provided cases are exhaustive. */
-  def isSyntheticDefaultCase(cdef: CaseDef): Boolean = unsplice(cdef) match {
-    case CaseDef(Bind(nme.DEFAULT_CASE, _), EmptyTree, _) => true
-    case _                                                  => false
-  }
-
   /** Does this CaseDef catch Throwable? */
   def catchesThrowable(cdef: CaseDef)(using Context): Boolean =
     catchesAllOf(cdef, defn.ThrowableType)

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

@@ -281,46 +281,24 @@ object StdNames {
 // ----- Term names -----------------------------------------
 
     // Compiler-internal
-    val ANYname: N                  = "<anyname>"
-    val COMPANION: N                = "<companion>"
     val CONSTRUCTOR: N              = "<init>"
     val STATIC_CONSTRUCTOR: N       = "<clinit>"
-    val DEFAULT_CASE: N             = "defaultCase$"
     val EVT2U: N                    = "evt2u$"
     val EQEQ_LOCAL_VAR: N           = "eqEqTemp$"
-    val FAKE_LOCAL_THIS: N          = "this$"
     val LAZY_FIELD_OFFSET: N        = "OFFSET$"
-    val LAZY_SLOW_SUFFIX: N         = "$lzycompute"
-    val UNIVERSE_BUILD_PREFIX: N    = "$u.build."
-    val UNIVERSE_BUILD: N           = "$u.build"
-    val UNIVERSE_PREFIX: N          = "$u."
-    val UNIVERSE_SHORT: N           = "$u"
-    val MIRROR_PREFIX: N            = "$m."
-    val MIRROR_SHORT: N             = "$m"
-    val MIRROR_UNTYPED: N           = "$m$untyped"
-    val NOT_NULL: N                 = "$nn"
-    val REIFY_FREE_PREFIX: N        = "free$"
-    val REIFY_FREE_THIS_SUFFIX: N   = "$this"
-    val REIFY_FREE_VALUE_SUFFIX: N  = "$value"
-    val REIFY_SYMDEF_PREFIX: N      = "symdef$"
     val OUTER: N                    = "$outer"
     val REFINE_CLASS: N             = "<refinement>"
     val ROOTPKG: N                  = "_root_"
-    val SELECTOR_DUMMY: N           = "<unapply-selector>"
     val SELF: N                     = "$this"
     val SKOLEM: N                   = "<skolem>"
-    val SPECIALIZED_INSTANCE: N     = "specInstance$"
-    val THIS: N                     = "_$this"
     val TRAIT_CONSTRUCTOR: N        = "$init$"
     val THROWS: N                   = "$throws"
     val U2EVT: N                    = "u2evt$"
     val ALLARGS: N                  = "$allArgs"
 
     final val Nil: N                = "Nil"
     final val Predef: N             = "Predef"
-    final val ScalaRunTime: N       = "ScalaRunTime"
     final val BoxedUnit: N          = "BoxedUnit"
-    final val Some: N               = "Some"
 
     val x_0 : N  = "x$0"
     val x_1 : N  = "x$1"